Thermal Expansion

If you're living in certain places, you may notice the next time you have your water heater replaced that it now has a sort of tiny replica of itself perched beside it or on top of it, or somewhere just slightly off to one side.

Building codes

That unit is a thermal expansion tank, and some cities are now requiring them as a part of their code, and for an excellent reason: hot water expands. A temperature and pressure relief valve is not a thermal expansion device. Now that backflow preventers have become part of areas with homes built after 2005; a thermal expansion tank might save you a fortune. A thermal expansion tank allows a place for hot water to go when it expands during the water heater’s heating process.

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How it works

From 90 degrees to 140 degrees, 40 gallons of hot water will expand by almost half a gallon. (think of a half gallon of milk to get an idea of the quantity.) A thermal expansion tank gives that extra water a place to go so it doesn’t put undue pressure on your plumbing. It used to be that the water would back up into the water main. With a backflow preventer, this is no longer the case.

In a closed system, this extra water won’t have a place to go, because water can’t be compressed. The pressure on the system increases.

If the system has a thermal expansion tank, no problem; the tank takes up the extra water, and the system is safe. But, without it, that extra half gallon has to go somewhere. Sometimes it will manifest as a leaky faucet. Sometimes, though, it will cause something more sinister, such as damage to your water heater.

The thermal expansion tank has a bladder inside it, which provides a place for water the flow. On the other side is pressurized air.

Testing

Once a year, you can test your water expansion tank, too, with nothing more elaborate than a tire pressure testing gauge. If the pressure is zero, or if water is leaking out of the valve during the test, there is a problem.

If the pressure is zero, you’ll have to add air to the tank, which you can do with a bike pump or air compressor. The PSI is written right on the tank. Just make sure you have the shower or a faucet (hot water) on when you do this.

If you have any questions about your thermal expansion tank, or if you’re having to replace a water heater tank every few years or so and don’t know why it might be you don’t have a thermal expansion tank and need one. Give us a call, and we will come out and take care of that for you.

If you need a licensed, bonded, experienced plumber for plumbing installation and service in Chandler, Gilbert, Mesa, Queen Creek, Ahwatukee or San Tan Valley call Norfleet Family Plumbing Heating and Air at 480-681-1764.