GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Electric radiant heat, extra insulation

DanCK | Posted in Energy Efficiency and Durability on

Hello. I’ve installed electric radiant heat in a customer’s kitchen which is partially over a laundry room and partially over a crawl space. Crawl space is well insulated with 2″ xps on the floor and closed cell spray foam on the walls. The customer still feels that the in floor warning over the crawl space is cooler. Think it would be worth while to install the foil backed insulation that’s used with hydronic in-floor heating to help? Besides putting a heater in the crawl space, I can’t think of much else can be done.

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. GBA Editor
    Martin Holladay | | #1

    Q. "Do you think it would be worthwhile to install the foil-backed insulation that's used with hydronic in-floor heating to help?"

    A. Yes.

  2. Dana1 | | #2

    It may be cheaper and better to insulate the walls of the crawlspace, converting it into conditioned space.

    Barring that, it may be cheaper & better to insulate between the floor joists with fluffy stuff. The 2" XPS should be sufficient thermal break to erase any temperature striping from the thermal bridging of the joists.

  3. DanCK | | #3

    Thanks Martin and D Dorsett. My original description may be a bit misleading but the walls of the crawl space have been insulated with closed cell spray in and the 2" XPS in on the concrete slab. There's about a 2' airspace between the top of the XPS and the bottom of the joist so still a little bit of room to get back in if the homeowner decides to insulate. The void is vented back into the basement as well so it should remain dry out there. Thanks for the feedback, much appriciated.

  4. Expert Member
    Dana Dorsett | | #4

    So you are saying there is no insulation directly under the active radiant layer and the subfloor, and the first insulating layer under the radiant is 2" of XPS under a slab more than two feet away?

    If that's the case, cheap R19 kraft faced batts snugged up to the subfloor between the joists should be good enough.

  5. DanCK | | #5

    Yes thats right dana. Cheers for the advice. Best to go to the homeowner with a few options. Thanks

  6. Expert Member
    Dana Dorsett | | #6

    As I understand it this is what you would have

    -finish flooring

    -radiant sheet & underlayments


    -R19 batts + joists (<<< add batts here, with no air between fiberglass & subfloor, facer on bottom stapled to joists.)
    -big air gap


    -2" foam

    This should be added under any of the radiant floor area including over the laundry room, not just the portion over the crawl space.

    [edited to reduce confusion about cross-posting while editing my prior post]

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |