There is no simple yes or no answer to this question. The Uniform Plumbing Code (UPC 604.13) states that “PEX tubing shall not be installed within the first 18 inches of piping connected to a water heater." But the UPC is not used in all jurisdictions. The International Plumbing Code (IPC), which applies to us here in Florida and other areas, does not have the same stipulation. 

    But the IPC does require following the manufacturer’s installation instructions; and some water heater manufacturers, especially of tankless water heaters, specify that PEX should not be directly connected to their product, with a minimum of 18” of other approved pipe at the water heater connection. The PEX installation manual of Zurn, a major pipe manufacturer, also has multiple requirements for the distance of PEX from a water heater pipe connection and also from a gas water heater flue.

    So, the sum of all this is that it depends on which code is followed in your area and what the manufacturer’s installation instructions say. And, incidentally, the PEX pipe shown at the top of the page is wrapped tightly with insulation for two reasons: 1) to keep the pipe from fracturing during a hard winter freeze, although PEX has enough flexibility to resist a minor freeze, and 2) manufacturers specify that it cannot be exposed to sunlight. 

    Also see our articles Frequently Asked Questions (FAQ) about PEX Pipe and Can I get insurance with PEX piping?

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Here’s links to a collection of more blog posts about WATER HEATERS:

• Does a tankless gas water heater still work with no electricity during a power outage?  

•  Why do water heaters have a sacrificial anode? 

• What is the difference between a manufactured/mobile home water heater and a regular water heater? 

• Does a tankless water heater require a pressure relief valve?

• When is a water heater drain pan required?

• Why is there water in my water heater drain pan? 

• What does it mean when a water heater Temperature/Pressure Relief (TPR) discharge pipe is "trapped"? 

• Can I leave a gas water heater in place when remodeling a garage into a family room or bedroom? 

• Where do I find the water heater in a mobile home?

• Does a tankless water heater in an attic require a drain pan? 

• Does an electric water heater require a disconnect? 

• Is a catch pan and drain piping required for a replacement water heater?

• What is the difference between a single element and dual element electric water heater? 

• What is an FVIR water heater?

• What is a dielectric union?

• What's that powdery crust on the pipe connections at the water heater? 

• What are the most common installation mistakes with water heater replacement?

• Why is my water heater making strange (rumbling, gurgling, knocking or banging) noises? 

• What can I do to make my water heater last longer?

• How can I determine the age of a water heater if the serial number is missing or decoding it is impossible? 

• How does a hydronic heating system work?

• What is the difference between a regular water heater and a direct vent water heater? 

• What is the difference between a regular water heater and a power vent water heater?

• What is backdrafting at a gas water heater? 

• How do I determine if a water heater is gas or electric?

• What does it mean when a gas appliance (water heater, furnace, or range) has been "red tagged"?  

• What's the valve with the flip-up handle on the water heater for?

• Why is an older water heater an insurance problem?

   Visit our WATER HEATERS page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.