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.