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Community and Q&A

Are can lights really that bad?

Brad H | Posted in Green Products and Materials on

I’ve seen the articles extolling the evilness of can lights and I can’t argue the old ones are really bad. But, would an airtight LED leak very much air? With an attic above you could pile a little extra cellulose above it to compensate for the 2-4″ you lose for the light. Most of the articles use the old lights as an example but don’t quantify how bad a modern airtight one would be.

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  1. User avatar
    Dana Dorsett | | #1

    Air tight means NO leakage, but are they really air tight?

    Most air tight recessed cans need some tape & goop to make them truly air tight. The quality of gaskets on gasketed fixtures also varies. The quality & durability of the air sealing during installation is everything.

    Low profile surface mount LEDs that mount into standard electrical boxes are pretty easy to make fully air tight to the ceiling gypsum, and only thin-out the insulation by ~1.5".

  2. Brad H | | #2

    Dana, any suggestions for a low profile surface mount LED's?

    I found the leakage spec, 2 CFM at 75 Pa.

  3. Eric Habegger | | #3

    I agree with Dana. I've attempted to do what he recommends in my own installation of Cree down lights in my own home. Sealing the perimeter flange is really important, but my preference is a gasket rather than a sealant. If you use a sealant you likely will have to destroy the light just to get it removed, possibly with attendant ceiling drywall damage.

    I'm closing in on being able to blower door test my home in a month or so I'll try to update what I find on this thread when that's done. I have a total of 20 pot lights installed. I'm doing almost all the work on my house myself so it's slow. Possibly the most important thing you have to plan for is to keep the pot lights well away from the perimeter of the house if you do not have a raised heel truss or similar construction. That's my situation and there simply is not enough height closer to the perimeter to pile insulation above the pot lights.

    One other thing of interest - I got the old style of Cree 4" lights and I've noticed there's very small passages for air to escape thru the holes holding the led light filter onto the assembly. I recently purchased a single updated model from them (at less than half the price of the original) and it appears to have a different mechanism to hold the filter on and there are no longer the obvious tiny holes for air to move through. So if you seal very well around the flange of the assembly they should be better.

  4. User avatar GBA Editor
    Martin Holladay | | #4

    The thin LED fixtures, installed with care by an installer who understands airtight details, can work well -- as long as there is room for extra insulation above.

  5. Brad H | | #5

    OK, going with thin LED fixtures which mount to a junction box. What is the best way to make these airtight? It seems that the best way would be to have the LED fixture be airtight, then you don't have to worry about the box, but the Access LED fixtures that I've looked at make no mention of airtightness.

  6. User avatar GBA Editor
    Martin Holladay | | #6

    There are lots of airtight electrical boxes available. The photo below comes from Home Depot.

    You can find other brands of airtight electrical boxes by Googling "airtight electrical box" or by entering "airtight electrical box" into the GBA search box.


  7. Brad H | | #7

    Sorry for all the naive questions, but I'm a newbie at this and I have to educate my builder and contractor at every step along the way on how to build an energy efficient house.

    That home depot box is only avail in canada, but I found a few. My electrician suggested just spray foaming around the box. Is there a reason why we shouldn't just do it this way? The smallplanet instructions say to spray the inside, so it doesn't seem like much labor savings to go with the airtight box.

  8. David Meiland | | #8

    Can lights aren't very air-tight, no matter what the packaging says. The insulation-contact / air-tight ("ICAT") types are certainly a lot better than the old ones, but they still leak air. It might only be a trickle of air, but it will be forever. With the easy availability of LED pucks like the Halo SLD series, there is absolutely no reason to use cans if you can live with the solid-lens look of the LEDs. I have used various types of air-tight electrical boxes with great success. You can make a typical electrical box air-tight with enough carefully-applied canned foam, but I worry about large blobs of foam breaking loose over time, and in any case, the cost of the foam starts to rival the cost of the air-tight box.

  9. Eric Habegger | | #9

    Reply to David:
    I don't think anyone has argued the fact that all can lights are very leaky. If you insert a led light with a flange that seals against the ceiling drywall then the leakiness of the "can" doesn't matter. Then the leakiness depends only on the flange seal against the drywall and the intrinsic leakiness of the led, which in most cases should be minimal.

    Having said that, you are right that the SLDs are more effective in stopping air leaks when combined with an electrical box that's airtight. Also, because of the reduced height of a standard box it allows for more insulation to be piled on top.

  10. Eric Habegger | | #10

    Reply to Brad,
    I've used airfoil boxes and they're the very best at stopping leaks. The passages for the foam on them are not for sealing the box to the ceiling drywall. That is already accomplished with the built in flange that fits against the drywall. The foam is simply to seal where the wires enter box. It's easy, foolproof, and a much better way to seal around the wires than in any other box I've seen.

    edit: I would order just 1 of them first just to find out if the protruding part of the light will fit inside the airfoil box before you do a whole boat load of them.

  11. Malcolm Taylor | | #11


    Don't take Small Planet's advice and spray foam the interior of the box.

    The box is an enclosure used to shelter the junction of electrical connections. Those connections may have to be checked or changed in the future and spray foam makes that a lot harder.

    There is also some debate as to whether spray foam affects the fill rating of the box by impeding its ability to dissipate heat. Some inspectors will not accept foam in boxes.

  12. Eric Habegger | | #12

    All the airfoil devices insulate only an internal channel where the wire entry point is. Malcolm, are they advising to fill up the internal volume with foam as well or are you assuming something you should not be assuming? I have never been tempted to do what you are suggesting, nor AFAIK is Small Planet advising such a thing. I think you may be missing the entire point of having a separate foam filled chamber that is entirely isolated from the electrical connections inside the box.

    It may be a moot point because there is a possibility that those chambers would not allow the light to fit.

  13. Steve Wilson | | #13

    Can anyone say whether the surface mount LED lights are outdoor rated for below zero temperatures? I am hoping to use them for the soffits on a new construction build.


  14. Brad H | | #14

    Thanks for the input guys.
    As stated earlier, I'm using junction boxes and flush mount LED.
    Eric, A gasket sealing surface between the light and the ceiling was what I was getting at in my Oct 16 post. But it doesn't appear to be the direction suggested by Martin, and most of the lights seem to just snap in place so I'm not sure how reliable that sealing surface would be, nor have I found one that touted that advantage. Perhaps in the high end lights.
    David, I'm not sure I share your concern about blobs of foam breaking off.
    So I'm looking at standard boxes and a couple of cans of foam and my labor (about 1 minute each?) to seal them up.
    Or special ordering airtight boxes, which might not interface well with the light. Possible schedule slip if they don't work. Still have to apply some foam. About $4 more for the boxes, so the cost is minimal but probably a little cheaper and just as good to seal up a standard box.
    Fair summary?

  15. Adam Emter | | #15

    I used about 40 round Airfoil boxes in my new house that I built. They are a fantastic product and have personally visited with the owner. I mounted "Thinklux" LED downlight fixtures in the boxes and they work perfectly. Not all downlights will work with the shape of the Airfoil boxes! Here are some photos from my installation.

  16. Malcolm Taylor | | #16


    You are right: I was assuming Brad was referring to standard boxes, not the air foil. As long as the foam stays in the two channels that look like a good solution.

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