Expansion Tank Tips
A water heater expansion tank helps to protect plumbing fixtures and pipes in those systems fitted with a back-flow preventer or pressure-restricting valve.
Your local building regulation may require an expansion tank to be installed during the installation of a new water heater, or as a retrofit installation to give an existing heater the protection it needs.
This installation involves the splicing of the cold water supply pipe at the top of the water heater and attaching an air-filled tank to act as an expansion vessel containing the heated water as it increases.
This DIY job is rather difficult and should only be done if you are experienced in plumbing.
Principles of an Expansion Tank
Your water heater can last even longer with an expansion tank, and in certain conditions, it is needed.
As the water heats up, it expands and can severely damage a closed system that does not have an expansion tank.
It is most important to have an expansion tank installed in closed systems that stop heated water from going back into the municipal main system with the help of a back-flow valve or pressure-restricting valve.
Within an expansion tank, there is an adjustable rubber diaphragm dividing the tank into two – one to accept water expanded due to heat, and the other serves as an air chamber which becomes a bit pressurized with every expansion of the diaphragm.
It May Be Mandatory to have an Expansion Tank
You may not need an expansion tank if your plumbing system is not fitted with some kind of backflow valve or pressure-restricting valve that keeps it closed.
Otherwise, it is advisable to have an expansion tank whether your local code requires it or not.
Tip: This installation makes use of sticks and existing copper pipes, but yours may differ based on pipe size, repiping and some other factors.
Do not hesitate to get a professional if at any time you are unsure of how to proceed.
Installation of an expansion tank is usually done right above the heater by attaching a tee-fitting to the cold water line.
Installation of the expansion tank is normally done vertically, though it can be installed horizontally if there are space constraints.
Your plumbing pipes as well as the orientation of your expansion tank will determine the kind of fittings you’ll need.
However, the connections are typically done using copper fittings and pipes.
The expansion tank typically comes with a threaded 3/4-inch fitting attached to the cold water pipe using a tee.
Install a Dielectric Union
After positioning the water heater correctly, install a dielectric union on the cold water supply access point.
Use pipe-sealing tape to wrap around the union threads and attach it to the water heater cold water inlet point using channel-lock pliers or a pipe wrench.
Install a Copper Adapter
Wrap teflon tape around the union’s top threads, and then thread a female adapter to the union.
Use channel-lock pliers or a pipe wrench to tighten securely.
Install Tee Fitting
Attach copper pipe of a short length as well as tee-fitting to the dielectric union adapter in the water heater.
The tee-fitting is normally positioned above the heater around one foot to provide enough space for the expansion tank.
Sweat-soldering is used by most plumbers for this connection, but push-fit connectors (also referred to as “shark-bite”) can also be used.
Install Expansion Tank Piping
Use push-fit connections or sweat-soldering to fix a copper pipe of a short length horizontally on the tee-fitting side outlet.
This pipe length is subject to the space available, but we recommend keeping it as short as possible – 6 inches or less.
Use push-fit connections or sweat-soldering to attach a female-threaded adapter at the horizontal pipe end.
Tip: Brass fittings and nipples are the best options to work with anytime.
Brass provides better weight support for your expansion tank than copper. Pipe support is best provided using clevis hanging from a beam.
Install Expansion Tank
Wrap the expansion tank threaded fitting with pipe-sealing tape and screw on the horizontal pipe threaded adapter.
Use your hand to tighten the screw, but be careful to avoid over-tightening so as not to damage the fittings or pipes.
Tip: You may want to install an additional valve to isolate the tank from your plumbing system.
Finish the Installation
Connect the tee-fitting top outlet into the cold water line by any means possible. This is normally done using copper flex pipe instead of static pipes.
Also, finish all the inlet pipe connections for hot water and turn on the heater. Run the water and test for any leaks.
Existing Water Heater Variations
The main difficulty in fitting an existing water heater with an expansion tank is getting adequate room for it.
There may be insufficient space around the water heater and this would require the use of pex pipes to create room for your expansion tank.
This usually requires you to replace the copper flex pipe to shorten or lengthen it, and maybe fit the cold water line with extra pipes and elbows.
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