Can PEX Be Connected to a Water Heater?

PEX piping is quickly becoming one of the most popular types of plumbing pipes in the United States. Despite its plastic composition, PEX tubing is flexible, malleable, easy to install, and shockingly durable. Because of its ease of installation and durability, many plumbers are wondering if they can connect PEX directly to a water heater.

Local building codes typically prohibit connecting PEX directly to a water heater. You can use PEX for the hot and cold water runs leading up to the water heater, but it can't be directly connected to the water heater itself if the code prohibits it. Instead, you typically need to use copper or flexible connectors specifically designed for water heaters.

Whether you can connect PEX directly to a water heater depends on your local building code and the type of water heater you're using. Most codes prohibit this, but not all. However, even if your local building code doesn't prohibit connecting PEX pipe to a water heater, it still might not be the best option. This article will examine whether it's a good idea and some alternatives if PEX isn't an option. 

PEX stands for cross-linked polyethylene, and it's made of high-density polymer polyethylene. PEX is hard and durable while maintaining flexibility because the polyethylene polymers are permanently cross-linked together. This is done through a chemical process that changes the high-density polyethylene into a thermoset rather than a thermoplastic.

These chemical and physical changes to the polyethylene turn it into PEX and give it the hard, flexible outer shell that PEX is famous for. These changes also make PEX tubing stronger, more durable, and more resistant to high and low temperatures. As such, it's the perfect type of tubing for plumbing applications in residential and commercial settings.

In addition to its outstanding physical characteristics, here are some of the reasons plumbers prefer PEX over other materials:

With copper, metal, PVC, and other types of rigid piping, you need a ton of fittings to go around bends and turns. However, while PEX fittings are available and easy to install, you don't always need to use them. Depending on the situation, you can simply bend the PEX tubing to meet your needs and skip fittings altogether.

PEX is by far the easiest type of piping system to install. You simply unroll the tube and take it to wherever you need to go. Because PEX is light, you also don't need as many hangers and supports as other pipes.

PEX piping is cheaper than other piping systems for two reasons. First, the cost of a roll of PEX is less than that of PVC, copper, and other types of pipe for cold and hot water systems. Second, PEX is extremely easy to install and requires fewer fittings, which means less money spent on installation.

Unlike copper and metal, PEX has no metal components and is 100% corrosion-resistant. PEX also holds up well against UV light if that's a factor in your area.

Because of its internal composition, PEX can withstand hot and cold temperatures, from freezing to 200 degrees Fahrenheit. This far exceeds most potable water systems, which means PEX is safe to use anywhere.

As with most plumbing questions, whether or not PEX is compatible with water heaters isn't a yes and no question. Instead, it depends on the following factors:

Because of how popular PEX has become, many manufacturers now produce it. Some types of PEX are better and more durable than others, so it's important to know what type of PEX you're using. PEX A, for instance, is the best type of PEX for hot water situations.

As we said before, your local building code is a huge factor. If you follow the Uniform Plumbing Code, you can't connect PEX directly to a water heater. However, if you follow the International Plumbing Code, you simply have to adhere to the PEX and water heater manufacturer's instructions.

Lastly, the type of domestic hot water heater you have will also affect whether or not you can use PEX. As long as your local plumbing code doesn't prevent it, it's perfectly fine to connect PEX to an electric water heater.

However, even if the local building code says it's okay, you shouldn't connect PEX directly to a gas water heater. The flue gas that emanates off of the vent pipe can melt PEX, resulting in a catastrophic leak. As such, keeping any PEX tubing at least 6" away from the vent pipe is essential.

If you've checked your local building code and it's okay to connect PEX tubing directly to a water heater, here's what you'll need:

• 3/4" PEX expansion crimpers, as 3/4" is the standard size requirement for a pipe-to-water heater connection
• PEX A expansion fittings
• Shutoff valve
• Flexible water heater connectors (optional)

Once you have all your tools and materials, you're ready to make your connection.

1. Set the hot water heater in place.
2. Measure the distance from the top of the water heater to your hot and cold supply pipes.
3. Cut your PEX pipe to match the measurements.
4. On the hot water side, connect PEX directly to the union connector on top of the water heater.
5. For the cold water side, install a shutoff valve 6-16" above where you connect the PEX directly to the union connector on the water heater.

Even if you have the option of connecting PEX directly to your water heater, it's easier to use flexible water heater connectors. This allows you to easily attach and detach the connection as needed, if you ever need to replace the electric heater.

The biggest mistake to avoid with PEX and water heaters is connecting PEX directly to a gas water heater. You also shouldn't connect directly to tankless water heaters, as they have a higher operating temperature and require copper or metal pipe. Additionally, if you use PEX in the run up to a gas water heater, keep the PEX at least 6" from the vent pipe to keep it from overheating.