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Community and Q&A

Air Sealing Lights

R Rafferty | Posted in Energy Efficiency and Durability on

Dear Martin,

A while back you had said about ceiling lights with an attic overhead: The best approach to air seal semi-flush lights which hang 12″ from the ceiling (and air flows around them) is to install airtight electrical boxes — for example, Airfoil boxes or Lessco boxes in the attic. We have old construction.

After contacting Airfoil, their boxes are only for new construction with open access. At 2.9″ Depth, I’m not sure the Lessco boxes will work either, as the 4″ round blue plastic electrical boxes we use (although for some lights we’ll use 4″ metal pancake boxes) are 2″ Deep. That doesn’t give much space around the electrical box, and it might not fit. (My electrician will take a look at this shortly to see if he thinks it would work, but you might know).

Those Tenmet boxes @ $20 each + shipping are fairly expensive for 16 lights. I’d rather find a box that we can caulk or foam down on the attic floor than build 16 boxes, which will get a little pricey for my electrician to do, but we’ll do that if we can’t find anything else. Please let me know about any other pre-made boxes for this application!

Thank you,

R Rafferty

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    R. Rafferty,
    If you are conscientious, you can seal the leaks in an ordinary electrical box with caulk or canned spray foam.

    If you are working from the interior, do your best to seal the leaks at the back of the box (where the cables enter the box) with caulk. Don't try to fill the box with spray foam; that would violate the electrical code (and be a fire hazard).

    After the drywall has been installed, seal the crack between the drywall and the electrical box with caulk.

    If you have access to the rear of the box from the attic, seal the back of the electrical box with canned spray foam. You still have to seal the crack between the drywall and the electrical box from the interior of the house.

    I hope you aren't planning to install any recessed can lights. Now that it's possible to buy pancake-thin LED fixtures that look like recessed can lights, there is absolutely no excuse anymore to install those dreadful recessed can lights.

  2. R Rafferty | | #2

    Ok, thank you! It's all old construction, so no drywall to be installed. And we do have access to the rear of the box from the attic. So, with that access, I think we only need to seal from the attic side. Please let me know if the interior side of the box AND the attic side should both be sealed! The only problem with canned spray foam is that it doesn't always stick to surfaces, and sometimes caulk doesn't stick too well, either. But we won't be installing any recessed can lights, ever, and the ones already there will be replaced with the thin LED fixtures.

  3. GBA Editor
    Martin Holladay | | #3

    R. Rafferty,
    Even if you don't plan to install new drywall, you must have some type of finish ceiling -- either old drywall, plaster, or perhaps tongue-and-groove boards. You still need to seal the gap between your finish ceiling and the electrical box with caulk; this work is best performed from below (from inside the house).

  4. Joe Suhrada | | #4

    Martin, do you have sources or vendors for the lights you are talking about? The pancake thin ones?

  5. Expert Member
    Malcolm Taylor | | #5
  6. Joe Suhrada | | #6

    Yes, I looked Martin, but these too are recessed and require a hole in the ceiling.

  7. GBA Editor
    Martin Holladay | | #7

    Joe,
    Here are links to two articles about the Philips SlimSurface lights:

    Rethinking Recessed Lighting

    Canned Lighting Conundrum

    Of course these fixtures require an electrical box -- any fixture does -- but only a shallow box. Shallow boxes are much easier to air seal that recessed can lights. Moreover, it's much easier to install insulation above a shallow electrical box than above a recessed can light.

  8. Joshua Van Tol | | #8

    Putty pads are another solution for sealing from the top side.

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