Thermal Expansion Tanks
What, might you ask, is a thermal expansion tank and why do I need one? Good question, considering a vast majority of the population has never heard of a thermal expansion tank and doesn’t have a clue as to why it’s suddenly so important to have one installed by their new hot water tank.
Of all the options for an installation of a water heater, the number one topic of debate is the necessity of the Thermal Expansion Tank. There’s no question about it. An expansion tank should be installed with every water heater every time. So often the thought is, “ my old water heater never had one, so why do I all of a sudden need one now?” It’s a simple matter of physics. Most people understand that when water is heated it expands. So, If water is expanding , where does this “extra” water go? The Expansion Tank. When sized right and installed correctly, it’s the expansion tank’s job to take on this “extra” water caused by thermal expansion. Thermal expansion tanks have a rubber bladder in them with an “air cushion” on one side and the other side connected to the water piping. When thermal expansion occurs, the water presses against the bladder and compresses the air cushion on the other side of the bladder to allow for that “extra” water to expand into the thermal expansion tank. When someone opens a faucet the compressed air presses on the bladder in the other direction to push the excess water back into the plumbing system. This device sized, tuned, and installed correctly minimizes excess pressure caused when water expands from being heated. Okay, so that’s the “what”. Now here’s the “why”.
In the past, expansion tanks were not as necessary as they are today. Back then, when thermal expansion would occur it would push the expanding water back through the plumbing system and into the city main. Today’s plumbing systems are more sophisticated, utilizing controls and other devices for efficiency and comfort. This often creates what is called a “closed system”, which prevents the expanding water from traveling back in the opposite direction. Many utilities have also been adding check valves to their water meters, so that once city water passes your meter it cannot flow back into the city supply. This makes your entire home a closed system. Since all of these things could potentially play a part in your plumbing system, the water is essentially trapped in this closed system until someone opens a valve. Imagine what happens when the water is heated in this closed system. With nowhere to go the pressure begins to increase substantially as the water tries to expand. This pressure could go well above normal working pressure, and could exceed 150-psi (pounds per square inch) if it weren’t for the safety relief valve. This valve is designed to open and relieve pressure from the water heater when it goes above 150-psi, draining to the floor, then outside the building where it won’t cause water damage. A system without a working expansion tank can face potentially large swings in water pressure, taxing the glass lining of the water heater, and other plumbing fixtures and components throughout the house. It could potentially be a small disaster in waiting.
The most common problem with expansion tanks is incorrect installation. Our technicians commonly run across expansion tanks that have failed prematurely and/or were installed incorrectly. Thermal expansion tanks must be properly sized, located, tuned, and checked annually during the annual water heater maintenance. A good installation will help maintain minimal pressure increase caused by thermal expansion, can reduce water hammer, and help protect plumbing components from strain. An incorrect installation can be as bad as having no expansion tank at all, and sometimes worse. Incorrect installation can be the cause of everything from high water bills and water hammer, to excessive wear on the water heater and plumbing fixtures.
So, now you have it, your physics lesson in thermal dynamics for the day. Not only can you impress friends and scientists with your new found knowledge, you can converse more confidently with your plumber next time you have a hot water heater installed. And we hope when that time comes, you’re having that conversation with a technician from Verne and Ellsworth Hann. Feel free to converse with us at 216-932-9755.
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