Can hot and cold water supplies (pex, 1/2") run adjacent to each other in a finished insulated wall on their way to a fixture? Is there a minimum required air gap between hot and cold, and/or should I add insulation between them?

(I’m in Vancouver BC)


2 Answers 2


I insulate the hot lines, everywhere. It's not that expensive, (or: "the cheap insulation is fine") and it keeps the hot and cold from affecting each other too much. Doesn't have a major impact on overall energy use unless you are recirculating hot for "instant hot water" (an insulated line still cools off between uses, unless the interval is quite short - if recirculating, the better insulation is probably worth the cost.)

For an insulated (exterior?) wall, be sure to keep the pipes closer to the inside wall, and you can just use pipe clips (or separate holes through the studs) to separate the pipes and let loose fill or dense pack insulate them, but actual pipe insulation is a bit more certain. Cutting batt insulation to fit around them strikes me as tedious, and my current understanding is that cellulose is superior anyway on several points.

  • i appreciate the different scenarios covered in your answer. the pipes run along the studs, in an interior wall between my unit and my building’s common area. it’s a fire rated wall with fiberglass and 5/8“ drywall. my initial concern was potential condensation building up over time but that may be an unfounded concern. no recirculation in my particular application, but it’s nice that you kept the advice generally applicable.
    – init_js
    Commented Jan 24, 2023 at 8:24

While I haven't used them I have seen looms that help keep long runs of Pex more uniform spaced and organized. They space the pipes about 3/4 inch apart.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.