Expansion tanks, also known as water heater or thermal expansion tanks, are one of the best ways to protect your plumbing system. They help protect your plumbing pipes and water heater from damage due to expanding water. Because of how commonplace thermal expansion tanks have become in modern plumbing, many people wonder if they’re required by code.
Expansion tanks are sometimes required by code, depending on where you live, the type of water heater, and the type of plumbing system. If you have an open plumbing system or a tankless water heater, you won’t need an expansion tank. However, if you have a closed system with a tanked water heater, an expansion tank will be required by code.
In this article, we’ll go into more detail about who needs a thermal expansion tank, and when there are code requirements. We’ll also explain the consequences of not having an expansion tank. Finally, we’ll dig into specific situations when it’s a good idea to have an expansion tank, even if the code doesn’t require it.
Table of Contents
Is an Expansion Tank Required by Code?
Whether or not an expansion tank is required by code depends on your water heater, plumbing system, and location.
If you live in an area with strict plumbing code requirements, it’s likely that an expansion tank is required by code. This requirement could apply whether or not you have a closed or open plumbing system.
Type of Plumbing System
While there aren’t a ton of national codes about expansion tanks, there is one stating that you must have an expansion tank if you have a closed plumbing system. A closed plumbing system is where water isn’t allowed to backflow out of your home’s plumbing system once it enters through the water main. Here’s the reason that expansion tanks are required on a closed plumbing system.
- When water heats up, it expands, sometimes up to 4%.
- So, if you have a 40-gallon water heater, there will be an extra half-gallon of water once it’s all heated up.
- On an open plumbing system, the extra water will simply backflow through the water main and back into the city plumbing system.
- On a closed plumbing system, however, water can’t backflow, which means the extra water needs somewhere to go.
- Thermal expansion tanks are installed so that the extra water can flow upward, into the tank, and wait to be redistributed when the water returns to its normal size.
- Without an expansion tank, the water would expand and potentially cause your pipes or water heater tank to burst.
Type of Water Heater
Finally, it’s important to note that expanding water only poses a problem to tanked water heaters. This includes traditional tanked water heaters of all sizes, heat pump water heaters, and any other water heater where water is heated and stored in a holding tank.
If you have a tankless water heater, water gets heated as needed, which means you don’t have a holding tank to store heated water. Therefore, you don’t need an expansion tank, even if you have a closed plumbing system or the local code requires an expansion tank.
When did Expansion Tanks Become Code?
Expansion tanks were first invented in 1954. While they’ve been around for more than half a century, they weren’t required by code until 2006. The problem of damaged plumbing systems on closed plumbing systems was prevalent, that the need for an expansion tank code became evident.
Expansion Tank Installation Code
If you want to find the specific wording and code when it comes to expansion tank requirements, it’s listed as IRC P2903.4. You can find it in chapter 29: Water Supply and Distribution in the 2018 edition of the International Residential Code, which is the official book of plumbing codes for the United States.
Under this code, expansion tanks are required for all new and replacement water heaters installed in a closed plumbing system.
Do I Need an Expansion Tank if I Have a Pressure Tank?
Contrary to what you may think, a pressure tank isn’t the same thing as a thermal expansion tank. Pressure tanks get installed to benefit your well pump and increase its lifespan and performance. Expansion tanks, on the other hand, are specifically for water heaters and for holding extra, hot water.
So, while the two plumbing components may seem similar, they aren’t interchangeable. Therefore, you need an expansion tank on a closed plumbing system whether you have a pressure tank or not.
What Happens if You Don’t Install an Expansion Tank?
If you don’t install an expansion tank on a closed plumbing system, you’ll most likely end up regretting it. Water is a powerful force, especially when it’s enclosed in pipes and plumbing fixtures that aren’t designed to handle it above certain pressures.
As we said earlier, water expands and increases roughly 4% when it gets hot enough. Additionally, there is extra water vapor that gets created by hot water heaters, which will add extra pressure. If water is exposed to the elements, this extra vapor and pressure evaporate. Or, if you have an open plumbing system, the extra water and pressure can backflow into the city’s plumbing pipes.
However, when it’s enclosed in pipes or tanks on a closed plumbing system the extra pressure has nowhere to go. Therefore, several things can happen in this situation if you don’t have an expansion tank.
- The sides of your water heater will expand, swell, and potentially burst from the extra pressure.
- One or more of your plumbing pipes will burst under extra pressure.
- The valves and pipes connected to the top of your water heater will burst or spring a leak.
Essentially, the extra pressure created by hot water will need somewhere to go, and it will exert pressure on your plumbing system until something gives.
Can You Run a Boiler Without an Expansion Tank?
As long as you have an open plumbing system or a pressure relief valve, you can run a boiler without an expansion tank. However, if you have a closed plumbing system and a tanked water heater, you need an expansion tank to operate your boiler.
Frequently Asked Questions
Do you need an expansion tank on a well?
An expansion tank has nothing to do with a well and you need an expansion tank on any closed plumbing system.
Do you need an expansion tank with a well pressure tank?
Expansion tanks only stand to benefit water heaters and have nothing to do with wells or well pressure tanks. You may, however, require a well pressure tank for your well pump.
Is an expansion tank required for a water heater?
Expansion tanks are only required for a water heater if you have a tanked water heater and a closed plumbing system. Otherwise, you should refer to your local plumbing code to determine whether or not you need an expansion tank for your water heater.
If you want to know what size expansion tank you need, check out this article.
As with most things in life and plumbing, thermal expansion tank requirements aren’t always black and white. The International Residential Plumbing Code states that you need an expansion tank on any closed plumbing system. However, if you have a tankless water heater or another method of getting rid of extra water pressure, you may not need an expansion tank.
While there are other methods of relieving water pressure, thermal expansion tanks are the most tried and true method. Therefore, if you have a closed plumbing system and a tanked water heater, you should adhere to plumbing code regulations and install an expansion tank.
Nick Lopresti is the founder of YourH2Home and a home improvement expert. He has years of experience writing about various home improvement topics, mostly as it pertains to water systems.