Does your water heater require a thermal expansion tank?

There is no correct answer on whether or not your water heater requires a thermal expansion tank. However, your home must be regularly updated to current codes when significant repairs, replacements or modifications occur. Unless these actions occur, a house is considered legal if it met the building codes in effect when it was built.

What Kind Of A Water Heater Do You Have?

If you have a tankless water heater, you need not worry about investing in an expression tank, as your water heater does not have a holding tank for the water. However, if your water heater is traditional tank style, you must check whether you have a closed or open loop water supply system.

Do you have a “closed” or “open” loop water supply system?

Some homes might operate on an “open” loop water supply system. In an open-loop water system, water can be pushed back into the water supply source, and no additional strain gets exerted on the water heater or the home’s plumbing. The expansion tank is not required in an “open” loop system.

However, today, several homes work on a closed-loop system with a one-way check valve installed on the water supply. These water supply - backflow preventer, double-check or RPZ are needed when on municipality (city) water, other water providers or if you have an irrigation (sprinkler) system connection.

If you have a closed loop system, you need to require a thermal expansion tank on your water heater the next time it is repaired or replaced.

How Does an Expansion tank help?

A thermal expansion tank is a type of canister that hooks onto the cold water pipe that feeds into the water heater inside the metal shell. It also contains a rubber diaphragm along with a pressurised pocket of air.

When the water pressure gets built, the water can overflow back towards the expression tank, where the flexible diaphragm allows some water to enter the volume of the tank area, thereby taking the pressure off the rigid pipes.

The air pressure that enters the water gets pushed back into the pipe systems when it cools.


This is how the expansion tank acts as a shock absorber reliving the increasing pressure without damaging the pipes or tanks.

Why a closed loop system needs an expansion tank?

When heated inside the water heater, the water expands, and pressure increases inside the tank. This is known as thermal expansion.

The expanded water then rises inside the tank and, when left unchecked, can cause the water heater to burst.

In an open plumbing system, water can quickly go out the way it comes into the water heater through the cold water inlet pipe.

But a closed loop system creates a single path for the water to enter (but not exit), and this extra water needs somewhere.

This is when an expansion tank is needed. When the pressure inside the waterheater gets too high, the extra water volume flows into the expansion tank to relieve the stress in the main tank.

An expansion tank will significantly increase the lifespan of your tank, and most manufacturers require a water heater in singapore to have an expansion tank for the former’s warranty to be valid.