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What is a Water Heater Expansion Tank?

A water heater expansion tank is a devise that is designed to help prevent fluctuations in water pressure. Too much water pressure or fluctuation in water pressure can cause damage to a home’s plumbing system, including the water heater, water piping and fixtures in the system. The water heater expansion tank absorbs excess water volume (pressure) caused by thermal expansion during the water heating process.

What is thermal expansion?

Thermal expansion always occurs in water heaters. When water is heated, like most substances, it expands.

Because water is non-compressible, it will increase in pressure if it does not have room to expand as it is heated. This excess pressure is especially prevalent in homes that have a closed water system.

How does a water heater expansion tank work?

A water heater expansion tank contains air, which is highly compressible. Expanding water from the water heater can flow into the expansion tank, where the air compresses, making room for the increased volume of water. Water pressure in the system doesn’t increase significantly.

What is a closed water system?

A closed water system is a system that has a one way valve, such as a backflow valve, check valve or pressure reducing valve installed. These one way valves allow water to enter the system from the main water supply, but prevents water from the water system flowing back into the main water supply. In a closed system, the extra water pressure caused by thermal expansion can cause damage because the extra pressure has nowhere to go since it cannot push back into the municipal water.

Even if you have not had a one way valve installed at your home, you may still have a closed system, because many municipal water providers are now installing check valves on main water lines to prevent possible contamination of the municipal supply caused by water backflow into the main system.

If I do not have a closed water system, do I still need an expansion tank?

You may still benefit from an expansion tank even if you do not have a closed water system. Expansion tanks are normally installed above the water heater on the cold water supply before it enters the water heater. The extra hot water from the thermal expansion can be stored in the expansion tank and when hot water is demanded, it is put back into the water heater. In addition, an expansion tank helps prevent dripping faucets and running toilets by keeping the extra built up pressure from reaching the fixtures and causing premature damage to them. If you are experiencing water hammer in your water supply system, an expansion tank can also help relieve this.

What if I do not know if I have a closed water system or not?

If you are not sure about what type of water supply system you have, call us. We will do a water pressure test of your system, and determine if you have a pressure regulator or check valve installed. In addition, if you have multiple water heaters, we can advise you if a single or multiple expansion tanks are required to safeguard you home. Expansion tanks are relatively inexpensive, and as in most cases, an ounce of prevention is worth several pounds of cure.