Recessed lights have received plenty of attention as a potential source of energy savings through the use of CFLs and, more recently, LED lamps. But even when equipped with the most efficient bulbs, can lights are a major source of undetected air leakage in most homes. Whether they are providing a pathway for air movement into floor systems or attics and ultimately out of the house, or drawing outside air into the house, they can affect air quality, comfort, and utility bills. This air movement is difficult to see or feel directly, but it can be easily detected using a smoke stick, especially in conjunction with a blower door.
A smoke stick reveals air movement through a recessed fixture in a house depressurized with a blower door.
Although newer homes may have fixtures rated for insulation contact (IC-rated), insulation is not enough to stop air leakage through the fixture. (In fact, you can often see evidence of air leakage in patches of dirt and dust that have collected on attic insulation above these fixtures.) Where you have access to the attic, you can insulate and air seal in one step by creating a "top hat" to isolate the fixture, sealing it to the surrounding structure, then insulating around it. A number of manufactured products are available to provide safe clearance for insulation around the fixture, but you can also build a box using scraps of rigid insulation or drywall. This video from Green Homes America shows how this works (and also provides a good overview of the air leakage issue with recessed lights).
This video from Green Homes America’s YouTube channel shows how to use a “top hat” to insulate and seal recessed fixtures from above when attic access is available.
Sealing From Below
In homes where attic access isn’t available or is difficult—and for recessed fixtures mounted in first floor ceilings—insulation is not an option. But because air can still leak out of the building through the can light, the fixture should be air sealed from below. Merely caulking under the trim ring is ineffective, however, because the fixture housing itself contains numerous slots and other openings through which air can escape. To seal recessed fixtures from below, you need to plug all of these voids.
One option is to use fire-rated foam, as demonstrated in this video from Goenergylink.
This video from goenergylink’s YouTube channel demonstrates how to use fire-rated spray foam to seal recessed lights from below.
Another option is to use a non-hardening, non-combustible duct sealant, such as GB Electrical Conduit Seal. Simply press the clay-like material into all of the slots, screw holes, and seams inside the fixture housing, as demonstrated in the video from Jetson Green.
Finish up by caulking the space between the housing and the drywall. You can slip the trim ring back into position without caulking it because all openings through which air might escape have already been plugged.—Sal Alfano