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The History (Evolution) of Water Heaters: Part II

Last month we began to talk about how tank-style storage water heaters have evolved into the devices we see today, and we’ll continue that here. We started by looking at the expansion tanks that are required on any closed water system, because there is so much interest in those little tanks and why they are needed.

However, historically the first main improvement that occurred due to all the explosions in storage water heaters was the addition of a safety valve that would ‘pop-off’ and relieve pressure buildup whenever there was too much heat or too much pressure. It’s called a temperature/pressure relief valve, or a T&P valve.

Around 1875, manufacturing changed ‘big-time’ when industry became able to produce big rolled plates. That was the beginning of large pressure vessels, from locomotives to boilers to big tanks of all sizes, and many other industrial applications. One of the outcomes of this new technology was that between 1870 and 1910, about 10,000 major explosions occurred in North America (about one boiler explosion every 36 hours). And though the number of explosions dramatically dropped after 1910 due to new safety relief valves being invented and used, they did still occur, causing injury, loss of life, and astronomical financial losses that translate to over $21 billion in today’s dollars.

Additional help was soon to follow. In 1914 the American Society of Mechanical Engineers (ASME) created the ASME Boiler & Pressure Vessel Code (BPVC) that regulates the design and construction of boilers and pressure vessels. This Code mandated the addition of pressure and/or temperature relief valves and systems, with proper design documentation submitted and approved on all pressure vessels. After many generations of improvements and changes, we now have the good quality, properly designed and manufactured temperature and relief valves for our water heaters.

These safety devices are no less important today than in years past, and every once in a while, someone tries to cut corners or in ignorance caps a dripping T&P valve, and huge explosions often result. (If interested, a recent series called ‘Myth Busters’ did a little demonstration on water heaters exploding when safety is ignored. Now, all water heaters have this, or a similar warning posted on it by the manufacturer:

And as mentioned, all manufacturers require that annual safety inspections be done. That includes ‘tripping’ the little lever on the T&P valve to make sure it will open and to see that it will close without dripping. Homeowners and property managers who choose to skip this annual inspection just because it’s inconvenient when the T&P valves keep dripping and have to be replaced would do well to remember…

…just one example of thousands that have occurred when a water heater has a T&P valve not working properly.

Next month we’ll try to wrap things up and look at the other improvements that have evolved with the humble water heater.


Bruce Davis, Sr.
President, Director of Education and Learning, Sales Manager, Licensed Journeyman Plumber, Licensed Electrician,
HVAC/R Electrical Administrator, HVAC/R, Certified WA State C.E.U. Instructor

Bruce Sr is President of Day & Nite Plumbing & Heating, a 67-year-old family owned and operated plumbing and heating business in Lynnwood, Washington. Bruce can be contacted at: Email: Bruce@dayandnite.net

Day & Nite Plumbing & Heating Inc. 16614 13th Ave. W. Lynnwood, WA 98037 800-972-7000

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D. Campbell

Very pleased with the professional technician, Donavan, who came out when our water heater quit working. This was the third major problem with this water heater, so we took his advice and replaced it. Thankfully, he was able to also install the new one right away. I had confidence in his advice and ability to do the job. He was thorough and friendly. It was a five star experience. I highly recommend.

D. Thomas

We had a great experience with Day and Nite from start to finish. Chris was great at the no obligation consult. He explained things clearly and covered everything but didn’t waste our time. They also provided lots of options and thoroughly explained them but never tried to push or up-sell us. Installation was fast and very professional. We will definitely be using Day and Nite in the future.

S. Lippold

Outstanding Service! Scheduler was pleasant and receptive. Technician (Collin) communicated well, arrived in the agreed upon time frame, diagnosed the problem and fixed the issue quickly. Previously, we had two other companies misdiagnose the problem and one company stand us up for a scheduled appointment. If we have plumbing issues in the future, Day & Night Plumbing will be our first call !

E. Rubio

I had the privilege to meet Zach on two separate occasions within a two week span. He was upfront and honest about the work that needed to be done. He is a hard-working, dedicated, professional employee of Day and Nite Plumbing. He explained what needed to be done. I asked questions and he was patient and explained things further so that I truly understood.

D. Lee

The technician was great: he knew exactly what the problem was and fixed it quickly and efficiently. Even when a glitch happened in the repair, he was totally prepared to handle the situation. I will definitely contact Day & Nite Plumbing for future problems. Thank you!

M. Lindell

Collin was our tech and he was very knowledgeable answered our questions and what they charged was very reasonable and we are very happy to have water again. I was really impressed by everyone that we dealt with they all were professional and helpful.

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