You may notice the next time you have your hot water heater replaced that it now has a sort of tiny replica of itself perched beside it or on top of it, kind of like one of those baby scorpions riding on the mama scorpion’s back.
This is a thermal expansion tank, and some cities are now requiring them as a part of their code, and for a very good reason: hot water expands. A temperature and pressure relief valve is not a thermal expansion device. Now that back-flow prevention devices have become part of homes built after 2005, a thermal expansion tank might save you a fortune. I’ll explain why.
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 actually back up into the water main. With a back-flow prevention device, 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 fine. 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 hot 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.
Once a year, you can test your water expansion than,, 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 is easily done with a bike pump or air compressor. The PSI is 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 this, or if you’re going through a hot 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.