Understanding Your Thermal Expansion Tank

If you have a tank-style water heater, the next time you have your water heater replaced, you might see that it now has a sort of tiny replica of itself perched beside it or on top of it, another little tank. Today we’re going to talk about that. It’s a thermal expansion tank, and its purpose is to protect your plumbing.

Hot water expands

Many cities are now requiring thermal expansion tanks 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 homes built after 2005, a thermal expansion tank might save you a fortune. 

Thermal expansion

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.) It used to be that the water would back up into the water main. A backflow preventer (another city code) doesn’t allow water to back into the main. 

Because the backflow preventer creates what we call a closed system, this extra water won’t have a place to go, because water can’t be compressed—the pressure on your plumbing 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 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 honest and experienced professional plumbing services for residential and commercial plumbing needs in Las Vegas, Henderson, and Enterprise give us a call at 702-766-3320.