View Full Version : Heat transfer between water lines?

09-08-2004, 05:52 AM
I am having a house built and the plumbing rough-in is complete. The water lines are PEX and there is a relatively long straight run (60') in the basement ceiling that supplies water to all the rooms above. I also have a return line for recirculating hot water because of the distance of the master bath from the water heater. All three lines (2-3/4" supply lines and 1-1/2" return line) are in the same set of holes in the joists running the length of the house. I have a feeling that since the hot water lines will always be hot due to the recirculation feature the cold water supply line will become warm. I have the plumber coming back tomorrow to discuss this issue and would like to know if there is a standard practice to separate the cold water supply line from the hot water line to avoid heat transfer. Is this a problem or just my imagination?

Dave G.

09-08-2004, 05:57 AM
It will be a problem. Even though PEX transfers heat at a slower rate than copper, it will eventually heat the cold water unless there is frequent cold water usage to keep it purged.

09-08-2004, 06:14 AM
It is common practice to install piping insulation (to save energy) and a timer and or aquastat on the HW recirculating line. If either was done the heat transfer to the cold line should not be a major issue. Another consideration should be friction among the piping being so close to each other. I'm not familiar with pex, cpvc or other plastic water supply lines but when it comes to copper lines, friction can be a problem.

09-08-2004, 09:07 AM
It's common to run pex (http://www.vanguardpipe.com/vanex.html) in bundles.
Unlike other type of pipe, heat transfer is not a problem.
instruction manual (http://www.vanguardpipe.com/pdfs/ManablocInstallationInst.pdf)

09-08-2004, 12:33 PM
Thanx for the link Terry. I guess I won't make a big issue of this. However, I can't imagine there won't be any heat transfer. After all, isn't PEX also used for radiant heating?

As for the idea of insulating the lines: that isn't practical since it is a tight bundle and no extra room in the joist holes to move the tubing apart. Hopefully, issues of thermal expansion causing friction problems will not appear either.

Thanx again,
Dave G.