Answering 8 FAQs about Water Heater Pressure Tanks

A standard tank water heater can strain your plumbing pipes and fixtures due to the normal thermal expansion that occurs when water is heated. This can be an issue in any closed-loop system that heats the water.

Water heaters and boilers for household heating systems are susceptible to this damage unless precautions are taken. A water heater expansion tank in a plumbing system can help reduce the risk of pressure damage to the pipes.

These eight simple questions will help you understand your water heater pressure tank better.

What is a Water Heater Expansion Tank?

A water heater expansion tank is a precautionary measure. It is an overflow vessel that relieves pressure created by the thermal expansion of water when heated.

How does a Water Heater Pressure Tank Work?

The water heater expansion tank functions as an overflow vessel, soaking up the increasing water volume caused by the changing water temperature and fluctuations in the water supply pressure.

Because heated water expands due to temperature increase, the water heater produces extra water volume as it heats the water. A conventional water heater can hold 50 gallons of cold water. 

However, as the temperature increases to 120 degrees Fahrenheit, the water expands to 52 gallons. This additional water volume may result in increased pressure in the water pipes. If the pressure is high enough, it can cause long-term damage to the water heater, sanitary fittings, and water pipes.

How to install a Water Heater Pressure Tank?

An expansion tank is typically installed just above the water heater using a tee fitting placed in the cold water delivery pipe. The expansion tank is typically mounted vertically, though it is acceptable to mount it horizontally if space is limited.

What's the Difference Between an Expansion Tank and a Pressure Tank?

The primary distinction between a pressure tank and an expansion is their functionality. An expansion tank controls water expansion and protects water valves and heaters. The pressure tank, on the other hand, increases the pump's lifespan.

What is the Ideal Pressure for My Expansion Tank?

Try to maintain the water pressure between 50 and 60 PSI. Thermal Expansion Tanks include an air bladder that expands and contracts in response to the expanded water from the water heater.

Is it Necessary to Have an Expansion Tank?

An expansion tank is always highly advised if you have a 'closed-loop system' caused by any check valve or pressure regulating valve installed on your home's water supply line. A common analogy is that having high water pressure in your home is equivalent to having high blood pressure.

How Can I Tell If My Expansion Tank is Functioning Correctly?

The tank should be filled with air and thus sound hollow. If it makes a dull thud instead of a hollow sound, indicating your tank is filled with water and needs to be repaired or replaced. You can also tell by feeling the tank. It will be cool where there is air and warm where there is water.

Why is My Expansion Tank Constantly Failing?

This can be caused by mineral debris or other deposits. Some older expansion tanks do not have the internal bladders in newer models. This component is what separates the water pressure from the air pressure. As a result, air can escape the tank and enter the water in your system, increasing the risk of damage.