Plumbing 101: Hot and Cold Water Lines Should Not Touch

Hot and cold PEX water lines ran through the same hole in a stud wall.  This is not a typical installation as both pipes should have their own holes to pass through the framing.
Hot and cold PEX water lines ran through the same hole in a stud wall. This is not a typical installation as 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 Building 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 ran over 25 feet through framing and are touching each other the entire way.This has passed the rough plumbing inspection and is ready for insulation and drywall.But this installation can cause some issues down the road and is not a typical supply run installation.

Typical Supply Installation

Typically, each hot and cold water line is ran through separate holes spaced between 2 and 6 inches apart depending on the amount of space that is available.The lines are ran independently for a few reasons.One reason is for ease of running the lines initially.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 degrees Fahrenheit while the hot water lines are going to be over 100 degrees Fahrenheit.This is a temperature differential of 40 degrees and will easily cause the cold water line to form mass condensation on the exterior coating of the line.

The Current Scenario

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 a possible issue.

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 have to just have a professional do it right the first time.

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Comments 3 comments

Giselle Maine 5 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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martys-tips 3 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.


Brian 2 years ago

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

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