Plumbing 101: Hot and Cold Water Lines Should Not Touch

Updated on January 6, 2018
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I am currently a licensed contractor performing remodeling services for residential and commercial customers in Wisconsin.

Hot and cold PEX water lines run through the same hole in a stud wall. This is not a typical installation; both pipes should have their own holes to pass through the framing.
Hot and cold PEX water lines run through the same hole in a stud wall. This is not a typical installation; both pipes should have their own holes to pass through the framing. | Source

One of the big discussions among building and trade professionals is the use of applicable knowledge and the International Residential Code (IRC) during inspections. While some issues are very obvious, even to the untrained eye, other issues take a bit of knowledge to catch.

The picture above is of PEX hot and cold water lines that have been run through the framing and are touching each other the entire way. This has passed the rough plumbing inspection and is ready for insulation and drywall. However, this installation can cause some issues down the road and is not a typical supply run installation.

Typical Supply Installation

Generally, each hot and cold water line is run through separate holes spaced between 2-6 inches apart, depending on the amount of space that is available. There are a few reasons for this. One reason is for easy installation. Another reason is so that when the water test is performed, the plumber can easily identify a leak if it occurs, and it is not uncommon to have a small leak in a pipe during the water test. The last reason that is not as obvious is so that the water lines do not conduct energy from each other and form condensation. Think about the amount of energy transfer that will occur with these pipes. The cold water lines are going to be around 60 oF while the hot water lines are going to be over 100 oF. This is a temperature differential of 40 degrees that will cause the cold water line to form mass condensation on the exterior coating of the line.

The Bottom Line

The plumbing pictured above has passed inspection as there is no code that states that this cannot be performed. However, a little extra knowledge would tell you that this is not a good plumbing practice and should be corrected to avoid possible issues in the future.

It is always a good idea to have a licensed plumber perform your plumbing work. Plumbing that is improperly installed can be extremely costly and will actually cost you three times as much as it would to just have a professional do it right the first time.

Questions & Answers

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      • profile image

        Brian 

        4 years ago

        Another problem with this installation -- sanitary tees should never be placed on their back. That is explicitly forbidden in the IRC.

      • martys-tips profile image

        Marty Boo 

        5 years ago

        When I saw the picture I instantly thought ,wow that's not good,Then I read your article it was a great way to explain the problems that installation would cause,great article.

      • profile image

        Giselle Maine 

        7 years ago

        Very helpful - I never knew about this, nor about the "why" behind the hot and cold water lines not touching.

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