A thermal expansion tank is a crucial part of your home plumbing system. Your thermal expansion tank is like the radiator overflow tank in your car. If you have a closed plumbing system (there is a check valve like this one ), then the plumbing code mandates a thermal expansion tank. You can read the 2015 UPC Plumbing Code here.
How Does It Work?
Inside of your thermal expansion tank there is a rubber bladder. This rubber bladder is filled with air until it matches the incoming water pressure. In Sioux Falls, SD we usually pump them up to between 75 and 80 psi. As your water heater heats the water inside the tank the water inside the tank expands. Water can be pressurized, but it cannot be compressed very easily. On the other hand, air is very easily compressed. If your drive a car or ride a bike, then you are riding on tires that are filled with compressed air.
The expansion tank is a safety device. As the water heater heats the water, the water inside the tank wants to expand. since water cannot be compressed and the check valve keeps the water from flowing back out through the water meter, this pressure builds inside the system. The pressure inside your plumbing system should never exceed 80 psi at the maximum. Our licensed plumbers have seen water pressure exceed 160 psi on a water heater without a thermal expansion system or a pressure regulating valve.
When you have a properly functioning expansion system that is inflated to the proper PSI your system will operate safely. As the water is heated it will expand into the reservoir tank and compress the air. Once a faucet is opened and the water heater turns off the compressed air will push out the gallon or so of water inside. This cycle will repeat throughout the lifespan of your water heater.
Do I really need one?
The answer is, yes. In our article about water heater pricing and code upgrades we discuss this very issue (read here). Ultimately, it all comes down to safety. The whole reason why the plumbing code exists is to protect your property, the life of your family, as well as the life and property of your neighbor.
How much does it cost?
All of this safety and assurance that your water heater will not burst is so affordable. Most of the systems our Comfort Heroes install cost between $250 and $400. This is a small price to pay for the peace of mind that your water wont burst, a faucet supply line won’t burst or a toilet fill valve won’t blow out.