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Q&A Spotlight

What To Do With All That Recessed Lighting?

A new homeowner weighs his options for stemming the heat loss from recessed can lights

Recessed lighting is unobtrusive, making it popular in kitchens and family rooms. But the fixtures also can allow air, heat, and moisture to escape into unconditioned spaces.
Image Credit: National Renewable Energy Laboratory

Justin Brown has moved into a house with lots of recessed lighting fixtures, including 10 six-inch Prescolite non-airtight fixtures on the second floor ceiling, and another 11 mounted in cathedral ceilings. He may have plenty of light in those rooms, but he’s more concerned about all the air that’s leaking into the attic and rafter bays and the heat loss that goes along with it.

In a Q&A post at Green Building Advisor, Brown writes, “I have explored all the options. The attic is covered with (I believe) R-30 batts and about 12 inches of blown-in cellulose on top of that. They put additional batts all around the fixtures like a moat but not on top of them — not sure why, since they are IC [insulation-contact] rated.”

In the attic, he’s considered building airtight boxes around the fixtures, but access there is difficult. Most of the fixtures are next to joists, and building the boxes would require a lot of fussy work. A more attractive option is an LED retrofit kit, which the manufacturer claims is airtight.

“I assume that will greatly cut down on air flow to the attic,” he writes. “If I install those and add some insulation directly over the cans in the attic, is that a good solution for cutting air passage and bolstering insulation in those areas?”

The retrofit kits are also IC-rated, and Brown wonders whether he can stuff some fiberglass insulation into the fixtures before installing the LED kits. That, at least, would cut down on some of the heat loss through the fixtures.

“Lastly,” he continues, “I know there are a lot of factors at play here, but can anyone help ballpark for me annual heat loss costs per can in a situation like this? I’ve seen $5 to $30 per can per year. I’m in New England, so winters are cold.”

Those are the issues for this Q&A Spotlight.

No easy way to calculate heat loss

“You have my sympathy,” writes GBA senior editor Martin Holladay. “It’s outrageous that there is no law against building houses with massive holes in the ceiling air barrier. I’m sorry that you bought a house with this problem.”

Holladay thinks that Brown’s plan to go with LED retrofits is a good one, and he doubts that stuffing some fiberglass insulation into the fixture is going to be a code violation.

But quantifying the annual heat loss from all those fixtures is too difficult.

“I’m not going to try to estimate the annual cost of the heat loss associated with these recessed can lights, because there are too many variables,” he says. “Suffice it to say that the air leakage associated with these fixtures is a major problem, and you are certainly justified in pursuing a solution.”

If it’s OK to use fiberglass insulation in the fixtures, Brown replies, what about using pieces of 2-inch-thick extruded polystyrene (XPS)?

“Regarding insulating inside the existing cans (recall both the current can housings and LED retrofits are IC-rated), would 2-inch XPS pushed tight inside the top of each recessed can cavity be an effective strategy?” Brown writes. “There would be about a 5-inch gap between the LED housing and the foam board. The LED retrofits would solve 99% of any air leaks… and the insulation would be to limit heat transfer where I can.”

No, don’t use XPS or fiberglass

Insulating the fixtures may help with heat loss, but using the wrong type of insulation could cause problems in the event of a fire.

“If you’re going to take this chance, don’t use XPS inside the can,” says Dana Dorsett. “XPS melts while burning, whereas polyiso chars in place, and has a higher kindling temperature than polystyrene.

“If doing it with fiber insulation,” he continues, “use rock wool rather than fiberglass. Fiberglass can melt in the presence of a fire, too. Rock wool cannot. Fiberglass is also prone to creating suspended glass particles in the conditioned space air if there is any air leakage from the attic to the conditioned space, and putting it right in the potential leak path probably makes that even more likely.”

In a scenario Dorsett lays out, the power supply in a cheap LED fixture blows a capacitor and starts a small electrical fire.

“You don’t want flaming melted polystyrene dripping out of of the fixture,” he says. “That can’t happen with rigid polyiso even if it persists long enough to light off the foam, but it totally can’t happen with rock wool, since even the steel of the fixture would begin to burn before the rock wool.”

Consider the type of fixture

The type of LED fixture that Brown is considering comes in either a 5-inch or 6-inch version. It’s sealed and gasketed, and covers the entire opening in the ceiling.

“Most LED recessed can retrofit assemblies rely on air convection to keep them cool,” Dorsett replies. “Don’t expect them to last as long in a sealed and insulated recessed fixture. The surface-mountable Philips units designed to be mounted to regular electrical boxes will probably last longer.”

The Philips fixtures with an outside diameter of 5.4 inches are roughly $50 each, he adds, with 7.9-inch models costing about $55. “There may be a way to cobble these (and an electrical box) inside your existing fixture stuffed full of rock wool, tossing out your trims,” he says.

What about adding more insulation in the attic?

Robert Hronek suggests more insulation could be added over the fixtures in the attic.

“I would think a guy could rent a machine and blow more insulation in the attic and fill up around the cans,” he says. “You wouldn’t have to get close to the cans as in crawling on your belly and building boxes. I even think you could spray foam right against the can if you were using LEDs. The LEDs put out very little heat compared to bulbs.”

Another way of adding insulation above the fixtures is to make airtight boxers from pieces of rigid foam insulation. “if you are using rigid foam to build airtight boxes around an IC-rated can light, is there a minimum distance the foam should be kept back from the can?” Michael Geoghegan asks. “Or does IC include rigid foam insulation as well?”

To that, Holladay replies, IC-rated fixtures do not require an air space between the fixtures and the insulation. But when it comes to spray foam insulation, he assumes some kind of barrier should be applied around the fixture before the foam goes on. “You don’t want to gum up the works of the fixture,” he says.

“There are several issues here,” Holladay adds. “One has to do with heat build-up, which is a problem that is obviously most severe with incandescent bulbs. Another issue has to do with the mechanics of insulation installation and the field practices of installers. If any spray foam installers are reading this, I’d be interested to hear whether they wrap IC-rated fixtures in some type of paper or cardboard before they spray around the fixtures.

“The third issue is the electrical code requirement that electrical boxes include a certain volume (expressed in cubic inches); this volume can’t be filled with insulation, because the air in the electrical box helps dissipate heat if there is a wiggly wire nut in the box. I’m not sure whether the prohibition against stuffing insulation into electrical boxes might apply in this case, but I suspect that it doesn’t.”

Our expert’s opinion

Here’s what GBA technical director Peter Yost has to say:

I see four main issues regarding the air-sealing and insulation of retrofit LED recessed can lights:

  • Creating an airtight ceiling penetration. I can’t tell you the number of times I have been told that the can lights themselves were airtight (when indeed they were not — read on), while the main source of air leakage was the unsealed penetration in the ceiling plane. In other words, air can leak between the hole in the drywall and the lighting trim. It seems self-evident that an airtight installation (including sealing of the ceiling penetration) is needed to support an airtight fixture. Look for LED can light retrofit kits that include a gasket as part of the trim package.
  • Insulating and air sealing the interior of the can light. I tried to contact four major lighting manufacturers on installation practices for LED can light retrofits. I only heard back from one: Lithonia Downlighting / Acuity Brands Lighting. The company strongly discouraged this approach because it likely voids the warranty on the fixture and obscures inspection or verification of the wiring of the assembly. Even though the wattage of the LED fixture is much less than the lamp it is replacing, there is still the need to shed heat generated during lamp operation.
  • Spray foaming the exterior of the can light. The technical rep from Lithonia also discouraged this practice because, depending on the construction details of any non-airtight metal can, they have found that significant spray foam can end up inside the can, with the same problems of wiring inspection. (Not to mention the issue of fire safety when spray foam is inside a can light, brought up earlier in this blog).
  • The choice between E-26 (screw-in socket lamps), GU-24 (lamps with prongs), and hard-wired LED retrofit can lights. I had not thought of this aspect of installation, but the Lithonia tech rep stated that California Title 24 now requires that LED retrofits be installed hard-wired instead of using either E-26 or GU-24 hook-ups. The idea is that if you air-seal and insulate the old can light assembly and allow a subsequent change back to an incandescent lamp, then you could have heat build-up and fire safety issues.

So how do you air seal and insulate IC-rated, non-airtight can assemblies? You build a box around the fixture that is airtight and then insulate around that. Or, you make the installation of an airtight retrofit can assembly a part of your LED retrofit.

Finally, it’s pretty amazing how much progress has been made with the color rendering index (CRI) and temperature ratings for LED lamps. Be sure to use these performance metrics in selecting your LED lamp. You can learn more about that here.


  1. W D | | #1

    Recessed Lighting Dilema
    I'm one of those unfortunates who bought a house with recessed fixtures. They were very popular apparently for quite some time. To me, they are a head ache. Sympathy doesn't help much but is accepted gratefully.

    I'm curious why only LED lights are discussed. Is there a place for CFL in the discussion? For example, is there a heat output difference? or other safety related differences? If the cans were designed for incandescent bulbs, surely they are over designed for lower power and lower heat designs like LED or CFL. Further, heat convection is not the only form of heat transfer. Can conduction/radiant heat transfer handle most or all of the load for LED?

    Like other retro topics, the recessed lighting fixture one is of interest to many homeowners. Trouble is, it's like trying to get usable advice from a lawyer. You hear more about what not to do than what to do or what's been tried.

  2. User avater GBA Editor
    Martin Holladay | | #2

    Response to W.D.
    An LED retrofit kit is not just a type of bulb. It is a kit designed to provide a solution to leaky recessed can fixtures. LED retrofit kits provide (a) a lamp that is thin; (b) a lamp that is efficient; (c) trim that has a gasket, thereby reducing air leakage.

    LED retrofit kits are now the most common way to address the recessed can problem. But this solution is not ideal, and it's not the only solution.

    If you are willing to remove the recessed cans, improve the insulation, and install an airtight electrical box that isn't very deep, that's a better solution. If you do this, you can then install any type of pendant fixture, surface-mounted fixture, or track lighting you want -- and you can use CFLs in these new fixtures if you like CFLs. The main disadvantage with this second approach is that it's more work.

    It's also possible to repair the ceiling with drywall plugs, so that there are no electrical boxes at all in your ceiling. If you take this approach, you can come up with a better lighting design that uses wall sconces or indirect cove lighting that bounces light off the ceiling.

    For more information on lighting design, see Martin’s 10 Rules of Lighting.

  3. User avater
    Dana Dorsett | | #3

    It's complicated
    CFLs are going away, losing market share to LED. CFLs have a shorter lifecycle and somewhat lower efficiency than LEDs, which is probably why the discussion is primarily around LEDs. Watts are watts- a 13 watt CFL puts out as much heat as a 13 watt LED, but most 13 watt LEDs put out more light than most 13 watt CFLs, and usually a somewhat higher quality light, as measured by color rendering index (CRI).

    A typical ~15 watt R30 form factor CFL used in recessed lights delivers ~45-50 lumens of light output per watt or about 700-750 lumens, and has CRI of about 80. A typical retrofit R30 LED runs about 55-70 lumens/watt, and are typically 10-12 watts, putting out as much light as a 15-16 watt CFL, and the CRI is typically 85+.

    Recessed cans designed for incandescent lights intentionally limit the conducted heat transfer for fire safety reasons, and are designed to convection cool the incandescent bulb. That's exactly the opposite of what you want with a CFL or LED, which is why early failure rates are high when installing CFLs & LEDs in recessed cans. So convection is really the bulk of the cooling capacity available. Incandesecents tolerate the high temps just fine, but it cooks LED & CFLs. With a base-up configuration the temperature sensitive power supply/ballast components in the highest temperature air inside the fixture, mounted to a relatively thermally isolated socket. The higher the wattage of the LED/CFL assembly the quicker the components will fail. That's another reason why purpose-made LED fixtures are a better solution than retrofit assemblies.

    Stuffing insulation inside the fixture might slow down the heat escape from the house, but it also raises the temperature of the Edison-base LED assembly, and will shorten it's service life. You may be able to insulate tight to the fixture (or even inside it) without causing a fire, but it's not really the ultimate solution to anything.

    Fixture such as the ~5" diameter 10 watt SlimSurface Philips low profile surface mount fixtures (comparable to R30 recessed cans in appearance) run about 65 lumens per watt, and the 90 CRI flavor isn't much more expensive than the 80 CRI version. At $50-55/pop it might be twice as much money as an Edison base retrofit assembly, but it's probably going to last more than twice as long when the old recessed can is both air-tight and insulated.


    Why do LEDS fail in light fixtures
    Is the heat build up the same reason LEDs fail inside enclosed light fixtures? Are there some LEDS that last longer or cool better in enclosed fixtures and recessed lights or are they all equal?

  5. User avater
    Dana Dorsett | | #5

    Yes it's the elevated temperature, but no, they're not equal.
    There are distinctions between vendors in terms of how well they tolerate the elevated tempertures, and it's usually a function of the quality of the heat sinking on the LED retrofit assembly.

    As a general rule, the lower the wattage, the longer it's likely to last, since the more watts you dump into the recessed fixture, the higher the temperature will be.

    It's also true the higher the lumens per watt, the longer it will last all else being equal, since a larger fraction of the power used is being emitted as light, not heat. So a 700 lumen LED that's only 9 watts (78lm / W ) will be pumping less heat into the recessed can than a 9 watt LED that's only 500 lumens (55 lm/ W ), but it takes a dramatic difference in efficiency before that's a factor.

    I'm with Martin- downlighting has low visual-efficacy due to the glare factor, and shadow casting. You can see better (even at even lower light levels) when the ambient light is being set by up-lighting, using the ceiling as a diffuser, such as cove-lighting, wall valences, or wall sconces. The bright-spot-in the ceiling approach is just shadow-casting glarey-bit, which is why it takes a whole sea of them to be able to see anything well. A predominance of downlighting only makes sense when the ceilings are too low to take advantage of uplighting (or if your spouse is totally infatuated with the 1950s lounge look. :-) )

  6. Malcolm Taylor | | #6

    For taking Selfies
    Portrait photographers will tell you that people look best when lit from the side. To put your best face forward remove the recessed fixtures and add wall lights or standing lamps. See how many more likes you get on Facebook.

  7. R Miller | | #7

    Simple and Not so Simple
    New Construction- Don't install them

    Old Construction- Spend the money get rid of them

  8. Doug McEvers | | #8

    Airtight Recessed Trim
    If the lights use a socket holder type trim this may help in reducing air leakage.

  9. Justin Brown | | #9

    Following up on my retrofit
    Hi Gang,

    I went ahead and installed 36 of these LED retrofits. They are tight to the drywall and have definitely cut down tremendously on air leakage.

    In my cathedral ceilings, where 12 cans are directly below a roof, I did cut squares of rock wool and stuff them inside the cans, leaving about 4" between the rockwool and the top of the LEDs. I did this because I cannot access the area on top of the cans.

    I am second-guessing this now -- should I remove the rockwool? I'm not worried about shortening the LED life -- they don't get very hot at all at 11 watts. I just don't want to do anything that increases a fire risk. These cans are the coldest since they are in a vented roof with no insulation over them.

    I did the same with stuffing rockwool in the cans between my 2nd floor and attic. I then climbed into the attic and laid fiberglass batts over the cans themselves which are IC-rated / thermally protected. The rest of the attic is blown-in cellulose but the previous owners kept all insulation away from the light cans, even though they have IC-rated tags on them. Odd.

    Would it be safer with the fixtures that lead to the attic to remove the rockwool from in the cans, and substitute the fiberglass laying over the cans in the attic with rockwool laying over the cans to be extra safe? For the cathedral cans, the rock wool in the can is my only real option, but if we think it's risky I will remove it.

    What makes this all the more confusing is that the LED retrofits themselves are also IC-rated.

    Thanks for turning this into an article and for all your help!

  10. User avater GBA Editor
    Martin Holladay | | #10

    Response to Justin Brown
    I don't think I can add to all of the opinions that have been expressed so far. The official answer is that you should remove the insulation from inside the cans.

    A more nuanced (but perhaps more risky) answer would be that you can use common sense: leave the lights on for an hour, and then open one up and determine how hot the light feels, to see whether you are getting a dangerous buildup of heat.

  11. Justin Brown | | #11

    Response to Martin
    Hi Martin,

    Thank you I appreciate your reply. I barely even use the lights under the cathedrals. I will do as you say -- I assume if I can touch all surfaces comfortably that's not excessive heat build up. So far it seems these 11-watt units put off very little heat.

    Also, the cans are IC-rated, do you think subbing the fiberglass batts I laid over the cans in the attic for r-23 rockwool batts is prudent (from an air permeability and safety standpoint) or totally not necessary?

    Thank you so much!!

  12. User avater GBA Editor
    Martin Holladay | | #12

    Response to Justin Brown
    If you have installed fiberglass batts on top of your IC-rated cans, I would leave the batts as they are. It's probably not worth changing the fiberglass batts for mineral wool batts -- especially since every trip to the attic disturbs the existing insulation in some way.

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