Can PEX Be Connected To A Hot Water Heater 

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Both hot and cold water distribution systems use PEX pipes extensively. The pipes are durable but cheap, easy to install, and highly flexible, allowing you to run them through walls and floors.

However, connecting it to a water heater is another ball game altogether.

You can’t connect PEX directly to a hot water heater unless the local code and manufacturer’s instructions approve it. If you have to use PEX, use metallic transition fittings made from copper or bronze to bridge the gap.

In this article, we will explore the good, the bad, and how to navigate when using PEX to connect to different hot water heaters.

pex pipes

Can PEX Be Connected To A Hot Water Heater?

The Uniform Plumbing Code 604.11.2 stipulates that; you shall not install a PEX tubing within the first eighteen inches of piping connected to a water heater. This code governs the installation and inspection of water heater connections, ensuring consumers’ safety and welfare.

Typically, metallic components form the bulk of the outlets of water heaters. The high heat conductivity of metals can take the temperatures at the connection points to well beyond 200 degrees Fahrenheit. 

While PEX has a high melting point, direct contact with components such as the flue vent connector may cause it to expand rapidly or distort. 

The 18-inch allowance UPC stipulates works on the premise that the connecting metal, usually copper, is easily affected by ambient temperature. It allows the hot water to cool slightly, effectively protecting the structural integrity of the PEX. 

Can PEX Be Connected To A TANKLESS Hot Water Heater

Unlike traditional water heaters, which have to hold water before heating it, tankless systems heat the water instantly as it passes through the device. 

Whereas the temperature control of modern tankless heaters is relatively consistent, you CAN NOT connect PEX directly to tankless hot water heaters. You need a minimum of 6-inch clearance between the exhaust vents and the tubing.

This is because the exhaust vents can go as high as 460 degrees Fahrenheit, above the maximum heat temperature the PEX pipe can handle (200° F.).

These heaters might have a high initial cost, but the long-term benefits give you value for money. Besides the low energy and water bills, they are safer, occupy less space, and provide an endless hot water supply as long as there is power. 

Tankless hot water heaters require very little maintenance and can last up to 20 years before you need to replace them.

Can Hot and Cold PEX Lines Touch

The hot and cold PEX lines should not touch unless you insulate the hot water pipes. Keep them at least 6 inches apart to prevent heat transfer between the lines.

It is worth noting that the color of the PEX pipes is solely for distinction. The color does not mean the tubing ratings are different; it simply helps you differentiate the cold from the hot water lines. You can interchangeably use the red and blue pipes for cold and hot water, respectively, and the building inspector will still give you a clean bill of health. 

How To Connect PEX To A Water Heater

PEX tubes are flexible, and you can easily modify them to connect to metal fittings without using heavy-duty tools. It would be best if you used the correct sizes for the connectors to prevent leaks at the junctions.

Some of the ways to make PEX connections are:

  1. Stainless Steel Clamps (SSC) – arguably the best option for potable water and hydronic heating applications. It involves tightening stainless steel rings around the PEX tube using a ratchet clamping tool.
  2. Crimp Rings – the rings can either be copper or brass. It is a relatively simple procedure with the tube and rings crimping tightly using a PEX clamping tool.
  3. Compression Fittings – it involves the use of a threaded brass nut and a tapered plastic compression ring. Tightening the nut squeezes the plastic compression ring creating a watertight seal.
  4. Push-fit Connectors – it is the quickest way to make PEX connections. You will not require any tools; find the compatible sizes and push the connecting pipes into the housing for a firm fit.

Regularly inspect the connections for defects and leaks. Re-tightened them if you experience any leaks but avoid using too much tension, which may damage the threads. You can also thread a PTFE clockwise over the leak at least three times.

Here is a video to connect all fittings in-house with PEX pipes:

Where Should I Install My Hot Water Heater?

Most building regulations will require you to place the heater against the wall of your house. Usually, garages and basements are the go-to options since they are spacious with limited human traffic. 

Often, you might be required to enclose the heater to keep children and pets away. It is a fairly simple process where you can construct a utility closet or a wall to encompass it. If these places experience very low temperatures, consider the insulation of the PEX pipes for energy efficiency.

Where Should You Not Use PEX

High-Temperature Areas

As the temperature increases, the operating pressure of PEX decreases steadily. ASTM rating for PEX pipes is 160 psi at 73°F and 80 psi at 200°F. 

Keep the pipe away from heat areas such as recessed lighting, gas vents, or scalding uninsulated metals.

Outside Use

For optimum functionality, you should use PEX indoors. Ultraviolet rays usually cause the PEX to disintegrate quickly. 

It hardens and eventually cracks within a few months of exposure to UV rays. You can use insulation or UV sterilizers to shield the PEX, but it is expensive.

Rodent-infested Areas

Despite the sturdiness of PEX, rodents can gnaw right through the tube. It will cause leaks and blockages when the rodents take residence in the PEX. 

If you live in a neighborhood with a perennial rodent problem, you are better off using more durable water piping solutions such as copper.

Final Words

While PEX is proven to handle high temperatures, do not connect it directly to a water heater unless the local plumbing code or the manufacturer okays it. Independent research has led to regular review of these directives, and some states have allowed the use of PEX.  

However, this does not cut across the board, and it’s best if you comply with the current local recommendations. Non- compliance can lead to damages or loss of property and life. Besides, building inspectors may not approve your project resulting in bureaucratic delays and costly replacement costs. 

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