Whether or not your water heater requires a hot water tank expansion tank to operate depends on what type of plumbing system you have. Homes either have an open or a closed water heater plumbing system and if yours is the latter, then you’ll need an expansion tank to allow your water heater to operate.
Most newer homes are built with a closed plumbing system rather than an open one, so it is very possible that your water heater needs an expansion tank. We’ll answer more questions below, such as what is an expansion tank, the role it plays, and more.
What is an Expansion Tank?
Expansion tanks are a component of a hot water heater. Residential expansion tanks look a lot like small propane tanks with an air valve on the top and a threaded pipe connection on the bottom. They are typically around the size of a basketball, though can be much bigger for larger water heaters.
What's the Purpose of an Expansion Tank?
Keeping your water heater system healthy often requires an expansion tank. As we've mentioned, a plumbing system is either open or closed. With an open water heater system, any water that has increased in volume and pressure due to heating is freely passed from the storage tank into the cold water supply line, eventually passing in through the municipal water system if the pressure is high enough.
In open water systems, there is nothing to prevent the water pressure from rising, so the pressure in the open system is equal to the supply pressure.
With a closed water heater system, however, water cannot expand beyond what the valves in the system allow. These values usually include a check value, pressure reduction valve, backflow prevention, mixing valve, and sometimes others. A closed plumbing system prevents water from flowing in the reverse, meaning it won’t go back into the city lines once entering your home's piping.
So what is the purpose of an expansion tank on a water heater? In a closed water system, the hot water expansion tank houses the increased pressure and expanded water.
An expansion tank is installed on the water supply pipe of the water heater and is designed to handle the thermal expansion of the water that occurs when the water heats up. The expansion tank prevents the water pressure from getting too high, thereby protecting your water system from being too hot, damage, or even an explosion.
Without a hot water tank expansion tank on a closed plumbing system, the water pressure could build and build, getting high enough to damage valves, plumbing fixtures, supply pipes, and even the water heater itself, causing water heater leakage and other serious harm. A properly installed expansion tank absorbs excess pressure and prevents issues like these.
How Long Do They Last?
There are many variables that make predicting the life expectancy of an expansion tank difficult to impossible. The quality of the tank, the skill of the installation technician, water quality, and proper inflation all have an effect on how long your expansion tank will last. Some tanks last as little as two years while others last as many as eight.
Always get your expansion tank installed by a skilled professional and consider replacing them no more than a year after the expansion tank warranty has expired. Otherwise, you may end up with a lot of water damage and no warranty to help you out.
Most expansion tanks have a one- to five-year warranty, so expect to replace yours every two to six years, and whenever you need to replace your hot water heater.
What Size Expansion Tank Do I Need?
You may be wondering how to install a water heater expansion tank, but you can’t do that without knowing what size you need. The size of the expansion tank required depends on the size of your water heater. The larger the water heater, the larger your expansion tank needs to be. There is no “one size fits all” option.
The two factors you need to consider is your water heater capacity (which can typically be found on your water heater’s factory label) and the household water pressure (which is measured in pounds per square inch and can usually be found by your home’s water pressure gauge).
Once you’ve determined your water heater’s capacity and the household water pressure, you can find an expansion tank to suit it by using sizing graphs or by consulting a licensed plumber. Typically a 2-gallon expansion tank works with a water heater with a 40 to 60-gallon capacity and a psi of 40 to 50. A 4.5-gallon expansion tank is needed for larger water heaters, such as ones that hold 80 gallons with 80 psi.
If you’re wondering how to install a water heater expansion tank, talk with your plumber for exact details for your specific water heater.
Don’t Wait for the Water Damage to Hit
John C. Flood is dedicated to answering your questions, offering you quality services, and always providing licensed, trained technicians for all your plumbing projects. If you need someone to diagnose your plumbing system, determine what expansion tank you need, or install an expansion tank, don’t hesitate to reach out to us for more information.
We're even offering $75 off any water heater installation.
It’s never a good idea to wait until water damages occur to get a professional in to look at your plumbing system.