What is this? A plumber type, writing an article on money?? The world is indeed a mysterious place… Well, you may remember that I wrote an article about “Asking the Right Questions”. That was from this blog, September, 2017. It seems to me that asking a good question about the way we view costs could be useful. You know that in our basic schooling in America, we get next to no education on finances and how money works. It’s up to us to figure it out for ourselves or find people good at money who can mentor us. I’m some mix of the two.
To define some terms here, “first cost” is just what it sounds like… “Life cycle cost” is different in that it takes all costs over time, and factors them in, to help one see what is a deal and what isn’t. What does something really cost? Let’s use a current example. Let’s say you want to buy a car, but you don’t imagine you have budget for something expensive, like a Tesla, so you’re looking at older Chevys. Just for fun, in comparing prices, you find a used Chevy for $10,000 and a used Tesla for $30,000. Let’s assume both cars already have 100,000 miles on them. Well, it seems obvious that you’ll save $20,000 by getting the Chevy. That’s first cost thinking!
Now let’s do this a different way. How many years will you get from the Chevy? If you maintain it well, you might get 100,000 more miles from it before it turns into a pile of oily rust. If you drive 20,000 miles per year, that’s five years before starting over again. The Tesla, because it’s mechanically far simpler than the Chevy should be good for 1,000,000 miles. (I did not make that up!) That means you’ll have 900,000 miles of driving before it turns to e-dust. That’s a good 45 years of driving at 20,000 miles per year. So, just from a replacement point of view, for $10,000 you get five years, or the cost of the Chevy is $2000 per year. Now, for $30,000 you get 45 years with the Tesla.That yearly cost is $667. Hmm, a savings of over $1300 per year! But wait, there’s more :~)
Let’s say the Chevy gets 15 miles per gallon. That’s 1,333 gallons of gas at $4 per gallon or $5332 for gas for one year. Some of the older Teslas come with free power for life… even for subsequent owners. So, that’s another chunk of yearly savings. There are other costs, like insurance and maintenance. To simplify this discussion, let’s just say those are the same for both cars, but we know that the gas vehicle will have higher maintenance costs than the electric one.
So, now let’s look at the yearly costs for both vehicles and determine how the life cycle costs compare. Initial cost are $10,000 for gas and $30,000 for electric.Gas vehicle costs are $5332 more per year than electric, but we can only extend this out for five years because the gas car then turns to rust. Then we repeat the cycle.
So, over ten years, the Tesla costs $30,000 and the Chevy (replaced once) costs $73,320! If you kept the Tesla for its full million miles, you would save something close to $300,000. That’s a nice little nest egg! The price of admittance was the $20,000 more for the Tesla, but it saved you $5332 in fuel every year along with purchase price savings of over $1300 per year. In fact, the break-even point is just around four years. After that you’ll be money ahead. Ultimately, that $20,000 investment made you $43,320 after ten years, or as much as $300,000.Not bad!
Oh wait! That money doesn’t need to sit there just getting moldy earning the same or less than the rate of inflation in a bank account. You get to invest it in something you know a lot about, like your business. I’ll be bringing up a tool (a saw) I got long ago in a little bit.With that saw, I built lots of things that people paid me for. I built decks, houses, and did remodel work… all using that saw. Way back when, the saw cost me around $35 or $40.It has helped to make me many tens of thousands of dollars. It really pays to invest in things that make you worth more to others, whether physical things or education. Doing this, that $300,000 could easily become millions. I like to ask myself when looking to buy something, “How cost effective will this be?” It’s a good way to differentiate between investment and entertainment.
It may be said that this was an extreme example, using cars chosen to make the point, but it applies to so many areas of life. When I buy tools that I know I’ll use a lot over time, I get good ones. I still have a Skillsaw that I got over 45 years ago. A cheap saw would have worn out many times over. When I’m looking for a tool for one time or rare usage, something cheap is just fine.
Investments that save energy also fall into the category where they can be judged for cost effectiveness. Yes, saving energy helps save the planet too, but I don’t wish to descend into politics. For this talk, we can look at “simple payback”, where, if a ten dollar investment in energy conservation saves a dollar per year, it pays for itself in ten years. But, also consider that if this was invested in your home, when the home is sold, you likely will get the entire ten dollars back as efficiency is something the new owners are likely to be interested in because it will save them money too.So, very roughly, instead of just paying for itself, your money was doubled.
So, consider asking the life cycle cost vs first cost question when you are looking at purchases, big and small. And know that investing in you is likely one of the best investments you can ever make.
Most people don’t really want to be thinking about plumbing materials… We just want plumbing to work flawlessly, forever! That’s nice, but reality does intervene sometimes and we then need to understand the practical considerations so we can get closer to our goals of flawless and forever.
So, here we go! Each piping material has different strengths and weaknesses. Sometimes the conditions piping will live in, or job site considerations affect which material or materials are best. Here I’ll go over some of the considerations that help to create a long lived, efficient and trouble-free system. I’ll take it one material at a time except where there may be interactions.
To start, we’re looking only at water distribution piping here. Drainage, fuels, or compressed air all have different considerations.
Let’s start with Galvanized Steel pipe, Pros:
PVC/CPVC Pipe Pros:
As a rule, it’s always easier to install smaller diameter piping. So, consider low flow fixtures when you remodel. This way you might be able to run really small stuff like 3/8” PEX, or soft copper (or smaller if allowed!). This becomes very much like running wiring, it’s so small and flexible. Also, it can be put in places that larger pipe wouldn’t fit, like flat raceway or hollowed baseboard.
This was just a quick overview, but hopefully it will help you to think less about and spend less time with plumbing. For fun, here’s a quote from Thomas Drummond, 1797-1840; “Property has its duties as well as its rights.”
I started using PEX piping in the early nineties and have long heard the rumor that rodents can chew through it. I've never actually seen a photo or known anybody with first-hand experience of this. To me, it had attained urban legend status, or perhaps my mind is from Missouri. So, imagine my surprise at seeing this. It's like staring into the eyes of a unicorn!
No doubt others have run across this many times, but for those who wondered about the myth, here's proof. You can see the stream of water leaving from the right side of the tube. This is a cold supply to a toilet and is half inch tube. Clearly the tube got chewed on a while ago as the wood around it has a lot of rot. Also the discoloration on the tube suggests it has been a highway for rodents. It had been wet for so long that the moisture had worked its way up right through the hardwood flooring and into the sheetrock wall.
This will be a job to fix with so much wood damage. Then there are the water bills. It makes me think rodent exclusion work is worth doing! The only plus is that I’ll keep that little piece of tube with the hole in it to use as a teaching tool for those who want to learn more about the nuances of plumbing. With this house, we’ll chase out the rats, then put up barriers to keep them out. That’s the best protection for PEX. In other situations, it can make sense to put the PEX in a conduit, like the grey PVC conduit used for electrical work, to keep rodents and their sharp little teeth at bay.
Ideally homes wouldn’t have places in them for rodents to call their own. Crawl spaces and attics don’t do much to make a home more livable, but they sure do invite critters! With some planning, it isn’t difficult to design a home so these unused spaces never get built, yet the function they give, access to mechanical and electrical systems, is still taken care of. That’s what I tried to do building my own house and so far the biggest invader has been ants. I found where they were getting in and caulked that, so no more ants! Actually one time a rat did get in. He had chewed through a plastic floor grate, so I went to metal.
Years ago somebody came up with the phrase, “Rust never sleeps.” No doubt rodents do sleep, but they probably take shifts, “working” on our houses.
The Hot Water Forum (HWF) has been around for about ten years, meeting yearly. I missed one, once and still regret it. It’s a mix of manufacturers, code folks, researchers, utilities, local, state and federal governments, engineers and the odd hot water nerd, like me. People come from all over the US and some other countries to attend. It’s the place to learn what new stuff is coming, from energy codes, to new product roll-outs, to finding civil ways of duking it out between competing utilities… there is nothing else at all like the HWF. The event is put on by The American Council for an Energy Efficient Economy, (ACEEE) https://aceee.org/conferences/2019/hwf . It’s a small conference, where everyone there is treated as a peer. I’ll guess that close to half of the participants are involved in giving presentations… so clearly there is a lot of know how in the room.
I moderated a panel on solar water heating this year. They even let me present a very brief history of solar thermal! For too long, there has been a tug between solar photovoltaic, (electric) and water heating, (thermal). One of my presenters had a collector that was electric on top and thermal on the back side. The idea has been floating around for years with nobody being that successful at it. But this one seems to work and has a good track record. On interesting thing is that if you keep photovoltaics (PV) cool, they work better. By collecting thermal energy as well as electric, the competition between energy outputs is gone and you get more electricity! Not bad.
Another fun thing was we got to tour the biggest water heater manufacturing plant in the world. It’s just outside of Nashville, Tennessee. They put us in an electric trolley and drove us around, so we could see just how heaters are made. They create a new heater roughly every 20 seconds. It’s rather impressive!
Back at the conference there was talk of a new kind of heat pump water heater, one that runs on 120 volts and can simply be plugged in. With California and other places looking to reduce their use of fossil fuels, this could be a game changer. Gas has long been considered to be a clean fuel, but nobody took into account how much gas the distribution systems leak, something on the order of five percent. Natural gas, or methane is a potent greenhouse gas and that much leakage makes it worse than burning coal, pollution-wise. There may still be good uses of methane, like capturing it from landfills and cattle ranches, and using it where it’s produced will largely eliminate the leakage concern. In California, about 90% of our water heaters are gas, yet the state is telling us we need to get off gas soon. This new heat pump could help make it possible.
One nice thing ACEEE does is to put up on the web all the slides from the presentations. They are organized by the year given and available for free. In the link above, you’ll see a link to “past hot water forums”. Please do go have a look. There is a LOT of good stuff there.
One last but rather important thing we’re learning is about pathogens in the water supply. The take away is that there are lots and lots of bugs in our water, not just legionella. Mostly they are not harmful, but there are still many that are. There are even bugs that are resistant to chlorine and chloramine! There are bugs that resist heat! Bugs live in the bio-films that form inside of pipes, particularly pipes that are oversized for the use, which is most plumbing. Codes have not caught up with the use of water saving fixtures, so flow rates in pipes are slower. This prevents the scrubbing that happens with higher flow rates and encourages bio-film growth. Turns out one of the most effective ways of dealing with bad bugs is to introduce good bugs. Who wants to do that? It would be a very hard sell.
It’s pretty easy to get into the technical weeds at the Hot Water Forum, and there is no better or more supportive group for doing so. It’s a perfect place for hot water nerds! If you are one, consider going. The HWF will be in Atlanta, Georgia next year.
The real world isn't an easy place to be idealistic about hot water systems and what could be. Many compromises are made in cost, quality, expectation and education. Money and ego play a part as well. We'd like to daydream out loud for a bit and share some 'what could be's" and 'only if's" as they relate to hot water.
The ideal water heating system would be supremely energy efficient. It would last as long as the building it was installed in. It would be a pleasure to live with. It would be absolutely safe and of course, the cost wouldn't be too much.
You're not going to get such an elegant system installed by a plumber who isn't thoroughly trained in hot water work, or one who may be more interested in bringing home the most dollars per job, rather than insuring your satisfaction. The challenge here is how to properly educate the workforce, not just in things technical, but also in business basics and management. Correctly trained plumbers wouldn't lose so much work to relatively unskilled (and possibly unsafe) handymen.
Fortunately, when it comes to efficiency and longevity, we have lots of examples from the past to help show us the way. In 1906, there were condensing water heaters which claimed 92% efficiency (most modern gas fired heaters are more like 60% efficient). Since these were point of use heaters, there were no distribution losses or waiting for hot water. These were 'bath heaters' and the downside is they weren't all that safe. There were also "U" tube heaters. In these gas fired, tank heaters, the flue went up, near the top, then turned 180 degrees and headed down again. It would exit near the bottom. This doubled the heat exchange area of the flue, but even better, stopped much of the standby loss gas heaters suffer from. Our daydream has modern hot water engineers looking at old designs like these in order to incorporate the good ideas from the past into today's heaters. We’ve collected a bunch of interesting old heaters which the General Society of Mechanics and Tradesmen in New York will be putting on permanent display. Hopefully it will serve as a resource to future hot water engineers and anyone who’s interested in hot water.
Have you heard of Monel? It’s a copper / nickel mix that is currently used on high end boat fittings. From the 1930s to the 1950s you could get water heaters made of Monel. These and copper tanks were often the last tank a homeowner would ever need to buy. Such long lived tanks are essentially not available now. Roughly 85% of the nine million or so water heaters made yearly are sold as replacements. The manufacturers seem convinced that low cost is the most important thing to buyers, so proven long lived tanks are just a memory. Our dream has manufacturers competing to produce the highest quality heater, just as their predecessors did, instead of competing to make the cheapest heater. There are exceptions, but they make up a tiny fraction of the market.
The cost of the hot water system needs to be put in perspective. Manufacturers and plumbers both compete on price, but how cost effective is something that needs more service and frequent replacement? End users would need to be educated in the hows and whys of life cycle costing, where all costs over time are taken into account. This is the only way to know what really is a good deal. This may be an area where government and other institutions could set a good example and help to retrain the home owning public. More demand for long lived equipment would help to make such equipment readily available at reasonable prices.
Just as there are rating systems for energy performance in new construction, we'd like to see the same thing done for hot water systems. Ratings could be based on total energy use per person, waiting times for hot water, etcetera. This could motivate plumbers to do better than just meet code. Gary Klein is working on that with his “hot water rectangle”, which is a way of looking at wet room placement in a building and being able to see in general just how efficient it may be. See: http://www.garykleinassociates.com/
Sediment is a problem in many modern heaters, particularly those with aluminum anode rods. One fix could be the "external flue" heater. This had a narrow flue wrapping completely around the tank instead of the central flue common in modern heaters. Aside from increased surface area for better heat transfer, this heater allowed the lower tank head to be domed down. Sediment would collect at the low point in the center and be easily removed by opening a drain valve attached there. With modern insulation, external flue heaters would have much lower standby losses, making them very attractive. Us moderns have to live with pounding and thumping in gas heaters because sediment is so hard to remove from today's tanks. Aluminum anodes contribute by adding a great volume of corrosion byproduct. Magnesium anodes (although slightly more expensive) used to be the norm and don't make such a mess.
In our daydream, metal distribution piping, stealing BTUs from the hot water and holding way too much water would be a relic of the inefficient past. Manifold systems using well insulated 3/8" PEX tubing (or even 1/4” tubing for short runs) would be the norm for medium sized and smaller homes. This method provides quick hot water delivery, has much less water waste, and is installed more like wiring than rigid pipe, making new construction simpler and retrofit much easier. Efficiency can be had with devices that use electronics, pumps and various other active things, but long term reliability is one of our goals. For example: You can cut standby heat loss from an electric water heater with a time clock or with heavy insulation. We would opt for the "nothing to go wrong" insulation first. Of course a timer could be added to keep the heater off during peak periods, but it IS one more thing to get out of whack.
In an effort to keep heat from being lost, we've paid a lot of attention to combustion efficiency and insulation, but then we let all that heat go down the drain. Going the extra distance to recapture those BTUs with drain line heat exchangers (which are now made for both vertical and horizontal applications) begins to make better sense as the actual costs, both monetary and otherwise become known. In our dream, long lived, efficient systems would have minimal environmental impact.
We've been watching the progress of a non-electric flue damper for some years. It is a simple and inexpensive device that fits under the draft hood and cuts standby losses at least thirty percent. That could amount to a huge savings, but somehow, the long and winding process of getting approvals, perhaps combined with egos and territorialism all conspire to keep the device off the market. It would be nice to see more regulators and industry representatives looking at the common good rather than their own turf. As energy and clean water grow ever more expensive, such turf wars must become less relevant. Now, if you put one of these dampers on an external flue heater, you'll have one simple and high performance water heater!
Please don't think we have pessimistic daydreams. All the necessary technology already exists. Together we have the talent and muscle necessary to make dreams of efficient, safe and easy to live with systems a reality. We are only lacking consensus of all the players.
There seem to be some misconceptions and false assumptions surrounding the use of expansion tanks, and we'd like to try to clear these up. The five W's provide a good framework for this, with a HOW? thrown in now and then for good measure.
The WHO is you, of course. You want to have a good understanding of expansion tanks so you can recognize and solve thermal expansion problems for your clients.
WHAT Is Thermal Expansion?
When cold water is heated, the water expands. This thermal expansion occurs in all residential and commercial plumbing systems that have tank-type water heaters. Though usually not a problem, thermal expansion can lead to high water pressure and cause expensive problems. The main reason to have an expansion tank in a domestic water system is to prevent the damage from high water pressure, defined as anything over 80 PSI.
In most cases, expanding water simply flows back into the main supply to the house. But thermal expansion is becoming more of a problem now because backflow preventers and pressure regulators are being used more frequently. As increased population has led to increased water demand, public water pressure has been more difficult to control. Building code now requires pressure regulators when pressure exceeds 80 PSI, and backflow preventers are sometimes required to prevent cross-contamination.
HOW Do Pressure Regulators Help?
Newer pressure regulators operate differently from most older ones. With a newer one in place, expanding water will pressurize the system up to line pressure, then flow into the main line through a check valve built into the regulator. Assuming the water heater's relief valve kicks in here as it should, this backflow will happen only if the line pressure is less than 150 PSI. (Note that in hard water areas, the check valve in the regulator tends to get stuck and so should not be depended on for protection.) Older regulators usually don't have that check valve. So with those older ones and with backflow preventers, the expanding water will simply build up pressure until the relief valve on the water heater drips (lucky) or something in the plumbing system breaks (unlucky). In either case, the plumbing is being subjected to high pressure and to large pressure fluctuations multiple times daily, and something is going to wear out.
WHAT Are Some High Pressure Problems?
High water pressure will add roughly 30% to the water bill just because more water flows out the tap every time it's used. High pressure makes relief valves leak, hiking the bill even higher. Water heaters suffer when high pressure cracks the glass lining, and you may even hear them groan as the metal flexes. High pressure causes faucet washers and automatic valves to wear out faster. Sink and washing machine hoses are more likely to burst. High pressure caused by thermal expansion produces uneven water flow, and it magnifies water hammer. For folks who have to deal with periodic water rationing, high water pressure causes not only higher water bills, but threatening letters from the water company and perhaps even a flow restrictor at the meter.
WHAT Can Mitigate The High Pressure?
Before expansion tanks were common, plumbers used to put an adjustable pressure relief valve in the system, anywhere downstream of the regulator. Often it was installed on outdoor plumbing and placed to drip on a flower bed; it was put close to the front door so the owner would notice if it dripped too much. However, relief valves used this way are made to operate so often they can fail quickly and leak all the time. Hard water makes the problem worse. Perhaps a better alternative is the Watts Governor 80. This is a toilet fill valve that is designed to relieve any pressure over 80 PSI. It has the advantage of being able to be used in any climate, not just where freezing isn't a worry.
WHEN Is An Expansion Tank The Best Choice?
The expansion tank offers a benefit the others cannot. Pressure will fluctuate very little with a correctly sized and inflated expansion tank. With the other methods, the pressure must go up fifteen to thirty PSI to operate the relief or fill valve. It's best to keep pressure as steady as can be and as low as possible (but still maintain good flow), particularly if water hammer is a concern. There's an advantage to using both an expansion tank and a relief valve in homes using a pressure regulator. In our hard water area, regulators last roughly five to ten years. Failed regulators are usually not discovered until someone notices a leaky relief valve on the water heater or some supply hose bursts. That's why it's a good idea to use both an expansion tank for thermal expansion and a relief valve installed in a visible location. This covers the bases and lets you know the regulator is failing sooner than later.
HOW Can You Assess Your Clients' Systems?
Start by checking static pressure with a gauge both before and after the regulator (assuming there is one). First check the upstream pressure. (You'd expect a reading well over 80 PSI since a regulator has been installed.) Next, run a small stream of water indoors and watch the gauge you've put downstream of the regulator. Turn off the faucet and see if the pressure creeps up to line pressure in just a few seconds. These checks will let you know if the regulator is working and if water is leaking by it. Running the water will also briefly take care of any thermal expansion that would show up on the gauge.
There is one more thing to check with the gauge. Make sure there are no leaks and ask that no one run water for about twenty minutes. Leaving your gauge downstream of the regulator, fire up the water heater. In a few minutes the gauge needle should start to rise. If it goes up to line pressure (as measured upstream of the pressure regulator) and stops, you know the check valve in the regulator is working correctly. If it continues to rise, you know the check valve doesn't work. If it goes up to 150 and stops, you know the relief valve on the water heater is working. If the gauge ever goes over 150 PSI, don't leave the premises without replacing the relief valve on the water heater, because the relief valve is no longer protecting against high pressure or, more importantly, high temperature. You can't risk having a client's house leveled by an exploding water heater. It's been our experience that about one quarter of the relief valves we test don't operate properly. Of those, nearly one in ten is plugged up and will not let water pass. Those are the dangerous ones.
HOW Should An Expansion Tank Be Sized And Pressurized?
If your test showed water pressure over 80 PSI (downstream) when the water heater fired, an expansion tank is definitely needed. Expansion tanks are sized to the volume of the water heater and plumbing. Get one that will take care of all of those gallons. Because of shipping regulations, tanks come pre-charged at only forty PSI. If your gauge showed 40 PSI as the household water pressure, you can leave it at that. Otherwise, pump it up to gauge pressure before installing it. (Pumping it up after installation works only if there is no water pressure against it.) This makes the most effective use of the tank. The bigger the difference between the air pressure in the tank and the actual water pressure, the less effective the tank will be at controlling thermal expansion.
WHERE Should The Tank Be Put?
The tank should be installed in a cold line. Anyone who wants to put it in a hot line should be prepared to get calls from clients complaining that hot water is now running from the cold taps; they may also tell you they particularly dislike the toilet steaming. What's going on? The expansion tank is pushing hot water back into the cold line when cold water is used and causing trouble for all concerned. The rubber diaphragm in the tank will probably have a shorter life in hot water, as well.
Heating systems and domestic hot water systems use different expansion tanks that should not be interchanged. Heating system tanks won't take the higher pressure or oxygen that DHW tanks are designed for. It may seem we're stating the obvious, but we have actually seen the wrong kind of tank installed.
WHAT Else Should You Consider?
Install the tank so it will be easy to service. At some point it may need to be recharged, and many years from now it's going to leak. So provide easy access. Take a look around and avoid placement where leaking could cause damage. Remember, it can go on any cold line downstream of the regulator. Be sure to install the tank with good support so that it will not sag down or strain the pipes when it has some water in it. Next, add an adjustable pressure relief valve or install a Watts Governor 80 in the toilet. If you use a relief valve, set it 20 PSI higher than the regulator setting. Install it so its drain line can be seen, and make sure to let your client know what a running relief valve means.
If a system involves old clogged steel plumbing, you may run into a few difficulties. If you set pressure down to the "right" level (ideally, 50-60 PSI), you may not get adequate flow from the taps. It might be necessary to increase the water pressure in the system and air pressure in the tank. If the main line is restricted, a larger expansion tank (like those used for wells) will help water delivery if it is installed where water comes into the house. Ultimately, the best fix for old, rusted steel piping is replacement. However, many clients resist that proposition, thinking it will be too much trouble.
WHY Use An Expansion Tank In A Domestic Water System?
We hope you can answer that question easily now. The need for expansion tanks isn't mysterious at all if you keep a pressure gauge handy with your tools. Used correctly, that gauge will demystify the complexities of pressure and flow and help you to take care of your clients' plumbing woes.
Article by Larry Weingarten & Zak Vetter
Way back in 1978, I (Larry) installed my first solar water heating system. I continued with solar thermal, installing new systems until tax credits left in 1986, then kept nearly all the local systems up and running for years after that. It became painfully obvious to me that simplicity is essential for the durability and longevity of any solar thermal system. Complex systems just die young. Back then, the holy grail of solar thermal was to come up with a system that would cost $1,000--which was never really done.
These days, you expect to pay $6,000 to $10,000 for a solar hot water system, installed. I have a friend, Martin Holladay, who wrote an article in March of 2012, titled “Solar Thermal is Dead.” He generated a lot of discussion with that article, including some dissent, so he wrote another article in December of 2014, “Solar Thermal is Really, Really Dead.” Martin looked at solar thermal prices and compared them to using photovoltaics (PV) and a heat-pump water heater to do the same job. After doing the math, PV and a heat pump appeared to beat solar thermal for water heating.
But, clearly, it depends on what your assumptions are! I’ll add that heat pumps are new enough that we don’t really know how long they will last. Also, good PV extracts about 20% of sunlight’s energy, while efficient solar thermal gathers around 80%, and even the “inefficient” system described in this article gets about 60%. These are reasons to continue to explore how to make solar thermal work.
Enter Zak Vetter. Zak asked me to help design and install a solar hot water system for him, but he had a set of goals I’d not heard before. He wanted:
Note that cost was not given as a limitation!
I had never worked with such a list. Many assumptions go into designing and building a traditional solar thermal system, and those got challenged by Zak’s goals. Here is a quick list of assumptions we typically work from:
Design rules also involve assumptions:
Clearly, Zak’s goals didn’t line up with the standard assumptions. But I’m glad he challenged convention, because ultimately we built a system that costs less and performs better than any solar thermal system I know of. The system cost right around $4,000 and provides for 95% of the yearly hot water need. A handy person could do the same job for around $3,000, if they built their own collectors.
Following is the thinking that got us there. Wanting efficient collectors forces us to build more complex, expensive systems due to overheating and freeze concerns. So, instead, we used really inefficient collectors! These are just coils of ¾” polyethylene tube, under an acrylic glazing.
There is no insulation in the collectors, so they cannot overheat and are unlikely to be damaged by freezing. The hottest we’ve measured in summer with no water flow is 170 F in the collectors, and they have frozen multiple times without problem. This type of collector has been under test in San Jose, California, for sixteen years with no trouble. Essentially, they are pool collectors, modified to produce domestic hot water, simply by adding glazing. They are commercially made by Gull Industries in San Jose. Here is what the coils look like installed on Zak’s roof.
The coils are 26 square feet each. Another benefit of using “inefficient” collectors is that we eliminated the need for copper pipe to and from them, by running PEX tubing. With traditional copper collectors that can stagnate in the summer sun at up to 400 degrees F, PEX tubing would melt pretty fast. But we were able to use poly pipe and PEX for nearly everything, simplifying the job even further. We purposely oversized the system, so it could coast through periods without sun and recover quickly when the sun returns.
The tank was another consideration. Normally, with any glass-lined tank (nearly all tank-type heaters in the US are glass-lined), you want to turn over the volume of the tank daily to prevent stagnation and odor problems. Turns out the anode that comes with all glass-lined tanks generates hydrogen gas, which some bacteria really like. We got around this by installing a 105-gallon Marathon tank, by Rheem. This is a non-metallic tank that needs no anode, so does not “age” the water. The benefit of this much storage is the ability to survive happily through sunless days. Here is what the tank looks like:
One other benefit of the Marathon tank is its insulation. It’s got three inches of foam, and the literature says it loses only five degrees F in 24 hours. Our data-logging suggests it’s more like six to eight degrees in our situation, but still, not bad. Insulation is something else we played with. Pipe insulation seldom comes really thick, yet keeping heat loss down increases the actual solar fraction and reduces the amount of back-up energy needed. So we decided to double up on the insulation where possible. Here are photos of how that worked:
Solar water heaters are normally designed as one- or two-tank systems. One tank is better, if you can make it work, as there is less equipment to lose heat from. These days, this can only be readily done with electric backup. So another thing we did was to disconnect the lower element in our single tank and use only the upper element for backup. This prevents the electric heat source from competing with the solar one. We wired it at 120 volts rather than 240, so there was no need to do anything more than just plug it in. It does take four times as long to heat at half the voltage, but Zak wanted a good test of the solar--so he hasn’t even plugged it in yet! The system was installed in November of 2014 and he has yet to use the back-up.
The system is managed simply with an off-the-shelf Goldline GL-30 solar controller. It measures the temperature at the solar collector and at the bottom of the tank. It compares the two and, when the collector is sufficiently hotter, turns on the pump. The control has adjustments for fine-tuning this set-point. Fortunately, we do not need the control for freeze or overheating protection.
The system was simple to install. If you look just at installation time, it took only six man-hours, which is very fast. In the good old days, a fast installation used to be three guys and one long day, or something like 24 person-hours. This system went in so quickly because:
Here are photos showing some of the time-saving hardware.
Performance so far has been good. We’ve data-logged at multiple points across the system in order to understand just how it’s working. Following is a graph of the Spring Equinox performance. You’ll see that the system produced water ranging from about 110F to a little over 140F.
The term “solar fraction” is used to indicate what percentage of one’s hot water is heated by the sun. Done right, determining the solar fraction would involve measuring total hot water use and subtracting the portion of water heating not provided by the sun.
We opted instead to simply notice when the solar-heated water was hot enough to shower with. If the stored water is around 105F or more, it’s good for showering. When we say the system is producing 95% of the hot water, it means Zak gets acceptable shower temps 95% of the time.
It’s a quick, non-mathematical way of understanding generally how the system is performing. If we took accurate measurements to determine solar fraction, it would probably be higher than 95%. But because we consider anything under 105 F inadequate, we’re presently not taking credit for water that isn’t quite hot enough, but is certainly well above groundwater temperature.
Following is a graph that shows the system at its worst. The vertical yellow bars represent periods of sunshine, and the vertical blue bars are night time. Between the 21st and 22nd you’ll even see rain! But note how just a few hours of winter sun on the 23rd gives the tank about a 20-degree boost.
Another two graphs show the differences between December and March. Note that, in these graphs, we measured outputs from each collector to see if all four were useful. It turns out that the first two collectors gathered more BTUs, but the following two collectors each bumped the temp up higher, so they really did help--particularly during the colder times of the year.
Where to go from here? Clearly there will be limitations on where this sort of system can be successfully installed. If these collectors are covered with snow, they might not function too well, so it could make sense to avoid areas that stay below freezing for extended periods of time.
Also, if tax credits are the main motivation, this system won’t do, as this collector/system isn’t yet SRCC-certified. Still, this system should cost less then most other systems, even without the benefit of tax credits.
There is a way to make the system cost even less, by making one's own collectors. It turns out you can buy enough of the right type of poly pipe to make a coil for $194, cutting collector cost by at least $300 each!
To wrap up, it’s clearly a good thing to bring fresh perspective to solar water heating. By intelligently questioning old ideas and by using newer materials and hardware, Zak pushed us to do better than I had believed possible!
Larry Weingarten was raised on the Monterey Peninsula of California and has been self-employed most of his working life. He got his general contractor's license in 1982. Larry has written articles on water heating and energy for various trade journals; has taught about these topics for PG&E, California State Parks, Affordable Comfort, and others; and has recently helped create DVDs on these and related topics. In 2006, he finished building an off-grid home; designed to be very efficient, comfortable, and inexpensive, it was the 13th home to meet the "1000 Home Challenge," a competition for creating superefficient homes. He likes cats.
Zak Vetter was also raised on the Monterey coast. He has been self-employed for over ten years, repairing and teaching about computers. Since 2008, Zak has been learning about the wide-ranging world of energy-efficiency while improving his own property. The solar water system in this article was inspired by a visit to Larry’s off-grid house, which demonstrated how much was possible with solar power.
This “article” began life as a worksheet, tied to the Water Heater Workbook. For years, I’ve been teaching classes on how to understand the life and death of water heaters. We do this by catching heaters on their way to the dump and then taking them apart. Sometimes fun tools like the Sawzall or really big pipe wrench get used. It’s instructive to actually see what happens to heaters over time in different conditions. You can even tell how much or how little the people who came into contact with the heater during its life, knew.
We start by figuring out how old the heater is, because you would expect different stories from a four year old heater than a forty year old one!
1) DETERMINE THE HEATER’S AGE This is done by looking for date codes on the heater itself, or the relief valve or the controls. Sometimes there is even a date code on the dip tube, inside the tank. Some of the main codes are: A81 means January of 1981, B81 would be February and so on. 181 also would mean January of 1981. 281 would be February. 8101 would be the first week of 1981, while 8152 would be the last week of 1981. Bradford White has their own code, which is available here: https://www.bradfordwhite.com/serial-number-date-code-reference-100#
2) LOOK AT HEATER FOR CLUES ABOUT DRAFTING If it’s a fuel fired heater, this can tell you how well the heater “breathes” and how safe, or not the heater is. If you see evidence of backdrafting, that means carbon monoxide may be getting into your living space. Not good!
Do you see any of these things?
Corrosion on the flue side of the nipple? (A clear indicator of backdrafting)
Melted insulation at the draft hood? (Same as above)
Ring of rust or discoloration on top of heater? (Acidic condensation may drip down onto the heater, causing a ring of rust, it’s a sign of poor draft)
Discoloration or soot around combustion chamber door? (This is where flames or hot gasses leap out of the combustion chamber, suggesting a blocked flue or other problem.)
3) LOOK IN COMBUSTION CHAMBER
Do you see any evidence of leakage in combustion chamber or flue? (This matters because there is no point in working on a tank that has already failed. This also is a first clue about the condition of the anode inside of the tank. If you find heavy or wet rust, the tank has leaked and is not worth fixing.)
4) REMOVE ANODE AND ASSESS CONDITION
Use: torque multiplier. (This is a tool that pros use as it works and helps prevent unnecessary strain on the person doing the work. Removing anodes can be challenging and having good tools really matters. Once the anode is out…)
Is the metal on the core wire depleted? (This lets you know how much life the anode has left.)
Is the anode magnesium or aluminum? (Aluminum is soft, easy to bend. Magnesium is stiff and a bit springy. I don’t like aluminum in tanks as I think it’s a health risk that we don’t need to take.)
Is it hex-head or a combination type? (If it’s a hex type, that means you could add another anode in the hot port!)
Is there anything unusual about it? (Here we’re looking for “passivation”, which basically means the anode has stopped working, or other stuff, like the rod being split, or chunks falling off.)
The ideal time to replace an anode is when six inches of core wire is exposed, the rod has even wear and is not coated over with a hard calcium buildup.
5) REMOVE OLD DRAIN
Use: crescent wrench & basin wrench; you may need a screw driver, hammer & rag. The first two tools are for removing the drain valve. The others are for removing any plastic remaining from the valve and for preventing much water from pouring out once that valve is removed.
What sort of drain was the original equipment? (The best drain is a full port ball valve. Between the tank and valve, you want a lined steel nipple and at the outlet of the valve, you want a hose adaptor.)
What, if any, difficulties were encountered in removing the old drain?
How big an opening is provided by that drain? (It’s fun to try and look through some factory valves. With some it’s hard to see how water or sediment could ever get through)
6) REMOVE NIPPLES ON TOP OF TANK
Use: pipe wrenches, including ratcheting type; you may need a hammer & chisel
What condition are they in? The point here is to see two things: are the steel nipples clogged up with rust, slowing flow and is there enough rust to weaken the threads, increasing the risk of leaks?
How does the tank look where they were attached? (Rust is the enemy!)
7) REMOVE DIP TUBE
Use: channel locks. This is done by sticking one handle of the tool down into the dip tube, then wiggle it around and pull up at the same time.
How does the dip tube look? Here you’re looking for cracks in the plastic, or holes, or even some or all of the tube broken off and missing.
Does it have any cracks or holes? If so, the cold incoming water will mix with the hot and give you a luke-warm shower :~[
8) TRY T&P LEVER TO SEE HOW IT FEELS: THEN REMOVE IT
Use: pipe wrench
Look at the back of valve to assess amount of sediment build-up.
Blow through it. If that doesn’t work, clearly a new valve is needed. This is really important as the relief valve is the last line of defense against the heater blowing up if things go bad.
This has been just a brief overview of how to look at a water heater. For a heater still in service, these steps will tell you if the heater is worth maintaining and how safe it is or isn’t. There is a lot more info at www.waterheaterrescue.com
For many experienced plumbers, there really isn't much to replacing a water heater. It's an easy job: just pick up one that matches what's there, maybe strap it in, and leave with the old tank. Whoa. What's wrong with this picture? Just this--it portrays the minimum. Unless you're quite happy with the amount of work you have, the amount of money you make, and the amount of satisfaction your work provides, it's to your advantage to be able to deliver the maximum. When you get jobs because you offer substantial benefits rather than the lowest price, you'll gain long-term, trusting clients and business from their friends, as well.
Stand out from your competition. Hot water can change from bread and butter work to something you can actually be proud of. Many clients will gladly pay for superior work. It's true that people often call just shopping for price. (If you look in the Yellow Pages, you'll see most all the ads shouting, "We cost less!" Inadvertently, plumbers' ads have been training consumers to focus on price for years.) Never mind. Stop and talk to these callers. Tell them how YOU install a heater. Explain how the extra things you do will save them both money and worry because the heater will be safer, perform better, and last much longer than an ordinary installation. Let them know that you can provide simple, ongoing maintenance to at least double the life of their new heater. In most cases, you can keep their heater going for as long as they live there. (Some of our clients' heaters are more than fifty years old.) Many people will be very interested in what you have to say.
Well, what do you need to know to provide this superior installation and follow-up maintenance? It's useful to start with an understanding of the things that make a water heater fail. Most people have only a partial picture of what goes on inside a water heater that affects its longevity. Corrosion, pressure, and heat are the three things that can do a heater in.
How do you control corrosion? The sacrificial anode is the magic wand. All glass-lined tanks have at least one. An anode is a magnesium or aluminum rod suspended inside the tank. It acts like a weak battery when the tank is filled with water. A slight current is generated between the anode and the steel tank (cathode). The current prevents rusting at any exposed steel parts such as welds, fitting penetrations, and pinholes or cracks in the glass coating. The glass does a good job of protecting the tank, but without an anode, a tank would last only a few years.
You don't need to buy an expensive ten-year tank to install a high quality heater. Longer warranted tanks have either a second anode or a more substantial single anode. When you put a new heater in, go ahead and buy a five-year tank. Then transform it into the equivalent of a ten-year tank at less cost by adding a second full-length magnesium anode in the hot outlet. (This combination rod has the magnesium suspended below a plastic-lined steel nipple.)
Anodes corrode away over time. In normal waters the anode should be checked every three to five years. If you can see six inches or more of the rod's core wire, replace it. If the tank has a second rod, you can wait longer, checking every four to six years. Softened water is another story. It's more conductive than normal water and forces anodes to corrode more quickly. Over-softened water can completely consume an anode in six months. Don't ever soften water down to zero hardness. Instead, leave 60-120 parts per million of calcium hardness in the water. That's better for metal piping, as well as anodes.
You can fight corrosion at plumbing hook-ups, too. Just as magnesium anodes corrode to protect steel, steel will corrode to protect brass and copper. Avoid using brass and copper in a steel tank. Instead, use plastic-lined nipples for all hook-ups, such as putting a brass valve or copper flex-line on steel pipe. This prevents damage to the steel. When you connect to the lined nipple with a copper flex-line, you've made a dielectric union that doesn't expose any steel to the water. Now it won't fill up with rust and cause trouble. Sometimes plumbers have trouble with leaky flex-lines. The problem is caused by the rubber washers in the ends of the lines. Heat makes them shrink, and they may leak after a year or so. Go back after six months and snug up the flex-lines, or instruct your client on tightening them. After it's been done once, the flex-lines will perform nicely long term.
Even though they're rated at 150 pounds, water heaters are happiest with fifty to sixty pounds of pressure in them. Both higher pressure and greatly fluctuating pressures can damage the glass lining over time. You've probably heard the crackling noise a new heater can make as it's filled and finishes pressurizing. That's the glass breaking as the steel stretches under pressure. Anodes have to work overtime in such tanks and won't last as long.
And if you hear a tank groan when water is run, take out your 0-200 psi pressure gauge (with a female hose adapter attached) and check pressure at the heater drain. You'll find it's too high. If you flush sediment from such a tank, you may see blue glass shards coming out the hose. Pressure can peel the glass lining off so it's no longer protecting the steel.
Solving pressure problems means both helping your clients and gaining a little more work for yourself. You may need a pressure reducer, expansion tank, and/or relief valve to take care of a high pressure problem. Carry your pressure gauge with you the way a termite inspector carries an ice pick. Use it to troubleshoot and locate problems.
Another pressure problem is water hammer. We've seen water hammer collapse the flue in gas heaters, and that definitely affects their performance! Sometimes water hammer is eliminated just by getting high pressure back down to normal. Otherwise, install water hammer arresters just upstream of any quick-closing valves to quiet down noise.
Heat is the third cause of water heater demise. When temperatures exceed 160 degrees, the glass lining of the tank begins to dissolve. Temperatures higher than 1000 degrees have been measured under heavy sediment build-up in gas heaters. You can control sediment to prevent heat damage and subsequent tank rusting.
You've probably heard the rumbling or popping sounds fuel-fired heaters can make. The noise originates in the sediment, and it seems to be caused by steam. Water overheats in the sediment and expands into bubbles of steam. When these bubbles hit cooler water, they instantly collapse to a tiny fraction of their former steamy selves. (A pound of water is about 1/1700th the size of a pound of steam.) This implosion creates a shock that we hear as rumbling or popping (or a burglar, or a freight train--we've heard some colorful descriptions.)
You can check to see if a tank has sediment. While the heater is firing, turn on a tap (either hot or cold) to lower the household water pressure. If there is a sediment build-up, you will hear the rumbling noise when the tap is opened. It will quiet down when you've closed the tap. At 50 psi water boils at 298 degrees (the higher the pressure the higher the boiling point). If there is sediment, the water trapped in it is overheating. Running a tap will lower the boiling point, so that the overheated water will flash into steam, making the noise we hear. A clean tank can't make that noise.
You need to get rid of the sediment to protect the tank from overheating. Much sediment can be flushed out if there's good water pressure and flow. You'll need a couple of new parts to make the flushing effective. First, replace that troublesome plastic drain valve with a brass ball valve. Use a lined nipple between tank and valve and put a hose adapter in the outboard end of the valve. To keep the valve from getting too hot, use a nipple at least three inches long. That way, scale won't form on the ball and the seals won't get scored when the valve is used. Voila--no drips! Now you have a large, easy-to-use valve that won't plug up with sediment during flushing. Second, remove the heater's factory-installed dip tube. Replace it with one that's curved at the end. Aim it straight back, away from the drain valve. When the valve is opened, the curved dip tube sends the water swirling around the tank, picking up sediment and sweeping it out the drain.
Overheating and noise problems are also caused by aluminum anode debris, as well as calcium sediment. As aluminum corrodes, it's able to produce nearly a thousand times its volume in gelatinous goo. It can make a six-month old tank rumble, creating a complaint you must deal with. So replace aluminum anodes with magnesium rods. (Avoiding aluminum also avoids some serious health problems associated with it.) It's not hard to identify the rods. Aluminum is soft and easy to bend, while magnesium is much stiffer and somewhat springy.
Those are the culprits: corrosion, pressure, and heat. Once you've taken measures to solve and/or prevent problems in these areas, expect the heaters you deal with to last a very long time. Since you also want to offer the safest and most efficient heaters possible, look outside the tank next.
Having a heater that lasts forever is nice, but meaningless if that heater is unsafe. Check out the following items for safety and reliability.
The temperature and pressure relief valve is a piece of plumbing most plumbers fear to touch. We're afraid NOT to. If you service a water heater, guess who the authorities are going to call if the tank later overheats and takes off like a rocket? It's you who will be blamed for the plugged T&P.
T&P valves need testing at least once a year. They can and do get clogged with debris. While testing sometimes results in annoying leaks, more importantly it can show that the valve no longer has the ability to keep the tank from blowing up. If the valve does not allow full flow or if it doesn't re-seat, replace it. In our area, about one of four valves doesn't work correctly. It's useful to hook up the relief valve with a union or flex connector as you run the line to a safe place. The union makes future checks much easier.
Vents can do a variety of unsafe things. They fall off, fill up with mortar from brick chimneys, get their caps plugged or pushed down, and they get installed with too much run and not enough rise, so draft is poor. In addition, heaters are put into rooms with slight negative air pressure, so that air is sometimes or always getting sucked down the vent pipe, spilling combustion fumes. Wait, there's more. Inadequate slope allows condensation to eat holes in the vent. Vents are run past wood, scorching it. And then, people pile boxes, plastic bottles, and other flammables next to hot vents.
Take a good look at the venting of heaters you install or service. Check to be sure that if a vent goes into an attic it also comes out. When the heater is fired up, spillage around the draft hood should be for only a few seconds. If combustibles are stored too near the heater or vent, talk to your clients and make a note on your invoice. If you see evidence of back-drafting, let them know about carbon monoxide detectors. Clients will appreciate your looking out for their safety.
Even with the large earthquakes of the not-too-distant past and with the codes mandating specific strapping, we still see new heaters installed with inadequate bracing. Quakes WILL happen. We just don't know when. Be sure your heaters are correctly strapped.
Probably not life-threatening, leaks can cause a whole lot of costly damage. So look around each job site to see what would be damaged if the water heater leaks. (And if it leaks for three weeks while the owners are in Tahiti?) If nothing will be hurt, you don't need a drain pan. Otherwise, you do. The pan also needs a drain line that's actually hooked up. (We've seen drain pan outlets just covered with duct tape, out of sight behind the heater.)
There are some interesting devices on the market now which are designed to shut off water supply to the heater if it starts leaking. Another option which might give your client peace of mind is a water alarm in the drain pan. To avoid false alarms or damage to the heater, run the drain line from the T&P out separately. Lines from both the T&P and drain pan should end where the homeowner will see them and be alerted to any leak.
Recent energy difficulties have raised awareness in consumers and plumbers alike. The need for efficiency in hot water systems is better understood and accepted. Correct heater sizing is one of the most important factors in the energy picture, but it's often overlooked. If you're called to replace a heater, don't automatically put in the same size. Ask some questions. Did the old tank provide adequate hot water? Have new fixtures been put in (low-flow showers, aerators, front-loading washing machines)? Check older showerheads. If you find an old 8 gpm showerhead, you can probably reduce the heater size by installing a low-flow shower. The energy savings will quickly pay for it. Smaller heaters always have a higher energy factor, due to lower heat loss.
Whatever the size, heaters with good insulation cost little more than their thinner counterparts. If you're installing a new heater and can get those extra inches of insulation to fit into place, your client will thank you for it. Tanks with R-16 insulation are readily available these days, and in popular sizes they can even cost less than the old standard R-8 heaters. Blankets aren't nearly as good as built-in insulation. Even the best blanket won't insulate your heater to R-16 (and you should not cover the top and lower portion of the heater). Another drawback is that blankets cover up safety and operating instructions; they can also hide evidence of leaks.
Go beyond the tank itself and install heat traps on the lines above the tank. Avoid the chattering ball type and install silent ones; you can make your own by using long flex connectors to make an upside-down U in the lines. Heat traps prevent errant BTU's from wandering away.
In addition, insulate those plumbing lines. Insulate as much hot line as you can and the cold line back five feet from the heater, if possible. Use 3/4" thick foam; it takes no more effort than putting in thinner stuff, and it does a much better job. Leave the ends of flex-lines or other unions uncovered, as you may need access and you don't want hidden leaks.
THE END RESULT
It's within your power to give your clients the most satisfactory water heating experience they've ever had. Long service life, safety, and efficiency are intertwined, and serviceability (the things you've built in which make the heater easy to maintain) overlaps all three areas. If you don't set up a heater so it's easy to service, maintenance probably won't happen. Forget trying to offer the cheapest heater. Instead, educate clients a little so they will let you give them an outstanding job. They'll be happy you took the time to show them a better way.
This is an article written years ago, but the message still resonates. Safety must come first!
A water heater exploded inside a restaurant in Southern California last year, killing one man, injuring several others and demolishing the rear of the building. Our purpose in writing about it a year later is not to second guess or affix blame. The precise cause or causes will probably never be known for certain. There is value, however, in looking at possible causes and contributing factors.
The water heater equipment at the El Torito restaurant was a fairly typical installation: a 726,000 BTU boiler, a ½ horse power pump and a 115 gallon, hot water storage tank. Water softening was provided by two adjacent tanks. Where are the potential weak points or trouble spots in such a set-up? We’ll explore several, some relating directly and others indirectly to the explosion.
One direct cause of the explosion was the lack of a temperature and pressure relief (T&P) valve on the storage tank, and a T&P is the last line of defense against overheating. When the system was installed six years earlier it is likely that a T&P was provided in the tank. For whatever reason, the T&P was plugged by the time the explosion occurred on August 1, 1993. You’ve seen leaky relief valves. It’s easy to imagine someone removed the annoyance from the tank, intending to replace it and then forgot about it. There was a pressure relief valve on the boiler, but that would not protect the tank from excess temperature as you’ll see.
One reason the tank explodes was that the water in the tank got too hot and there was no T&P relief. Now, how and why did the water get too hot?
We can deduce with some certainty that rusting was well under way inside the tank. First, the tank was six years old, and tanks which are not maintained, have generally begun to deteriorate by that time. (How many stories have you heard about five-year tanks giving out in five years and one day?) Second, this storage tank was fed with softened water. Since salt in softened water easily doubles or triples the consumption of a tank’s sacrificial anode, this tank had probably been without rust protection for several of its six years. (We’ve seen anodes completely consumed in as little as six months in over-softened water conditions.)
So the tank was most likely rusting away from both inside and out. Any number of conditions could have caused the weakened metal to fail--a restriction on the cold inlet, which blocked the expansion caused by heating, a water hammer caused by an automatic valve, or even a faucet closing. Fluctuation in line pressure could have done it. Or, if one too many molecules of steel rusted away, the bottom of the tank would begin to deform, cracking the already weakened metal and causing it to break. Once broken, a large leak would develop, instantly allowing the super-heated water to flash into steam with explosive results.
To get a clear picture of what happened to the tank at El Torito, you have to re-think your concept of water. Think of water as rocket fuel. And think of the steel tank, which holds the fuel as paper. With enough force, the tank will tear and wrinkle, just like paper does. Imagine that the static pressure involved here is 50 pounds per square inch (psi). The 18 inch diameter of the tank’s bottom has about 354 square inches, so that amounts to 12,700 pounds of pressure against the bottom… over six tons!
With a normal water leak, the pressure will drop as the leak grows, limiting the size of the tear. But with super-heated water/rocket fuel, the pressure will not fall off until much of the water turns to steam. The tank may already be through the roof by then! (Did you know a pound of steam is 1,700 times bigger than a pound of water?)
What ignited the rocket at El Torito? We imagine it was a combination of excessive rusting of the tank, some form of overpressure or water hammer and water which was heated over 212 degrees.
Whether or not incorrect equipment installation, improper equipment operation or equipment failure occurred is a moot point. It’s more productive to focus on the things which will make the system less dangerous.
It’s likely that people monkeyed with the controls, and not knowing all the effects of what they were doing led to an unsafe condition. To avoid this situation in your own work, talk to the people who actually use the equipment. Talk to the dishwasher. Is he satisfied with the hot water supply? Listen to any complaints or comments people have. Although they may not understand how the equipment functions, they know what it does or doesn’t do. Thy will give you the information you need to keep the equipment behaving, and that will help you to keep unskilled hands off the controls. Ask directly if anyone else adjusts or operates the equipment. Look for evidence of others’ work, like loose access covers, wrench marks or inappropriate settings. It’s not in anyone’s best interest to have unskilled hands on the equipment.
A comprehensive service routine and printed forms are needed to make sure regularly scheduled service/maintenance is adequate and complete. Mechanics may lose the ability to really see a system, especially one they’ve taken care of for a long time. Over familiarity can lead them to feel they know what components need maintenance, so some other parts may not be checked as well or as often as they should be.
It’s important to devise and use forms that require service and inspection information to be written down.
Keeping written records is still important even though we all use computers now. I like putting service info directly on the equipment, so it can’t be lost or ignored too easily.
Looking back over my working life of 50+ years, it seems clear that self sufficiency has always been the best way for me to be useful. Now, mix in a strong interest in water in its many forms and the wide world of animals and you'll know what's important to me.