Recessed “can” ceiling fixtures, or downlights, are the most popular home lighting fixture in the United States. However, recessed can fixtures can be energy intensive in the following ways:

• If they are not approved for insulation contact and are installed in an insulated ceiling, insulation has to be kept at least 3 inches from the fixture all the way around, leaving about 1 square foot of uninsulated ceiling space.
• Many homeowners and contractors install incandescent bulbs or R-lamps in the fixtures; these use four times the electricity of fluorescents and six times the electricity of LEDs, as well as generating heat that adds to air-conditioning loads.
• If the cans are not airtight, they allow conditioned air to escape from the living area into unconditioned spaces such as the attic.

Leaky recessed cans are an even greater issue than a hole in the ceiling. A non-airtight recessed can with an incandescent bulb can draw 3 to 5 times as much air as a hole the same size, thanks to the stack effect (Figure 1). When the light inside the can is turned on, the heat it generates turns the can fixture into a chimney, pulling air from the house up into the attic (McCullough and Gordon 2002).

Recessed downlights that are installed in insulated ceilings are now required by code to be rated for insulation contact (IC) so that insulation can be placed over them. The housing of the fixture should also be rated airtight to prevent conditioned air from escaping into the ceiling cavity or attic, and unconditioned air from infiltrating the conditioned space. The fixture should bear a label showing it meets the ASTM E 283 requirement of ≤ 2.0 cfm of air movement from the conditioned space to the ceiling cavity when tested at 75 Pa, and the housing should be caulked or gasketed where it meets the ceiling (Lstiburek 2009). Some brands of can lights designated ICAT may still leak air. Check the fixtures you intend to use to see whether they appear to be well designed to be air tight. See the guide Insulating and Air Sealing Existing Non-ICAT Recessed Lights for more information.

If recessed lights are installed in insulated cathedral ceilings, there must be insulation with an R-value of R-10 or greater above the can in IECC climate zones 4 and higher to minimize condensation potential. Extra caution should be taken to ensure the recessed can is airtight in unventilated cathedral ceilings. Leaky light fixtures can allow moisture-laden indoor air to enter the roof assembly. If the moisture encounters cold roof sheathing, it can condense, leading to moisture accumulation and rot (Holladay 2011).

Some building scientists recommend against putting recessed can lights in cathedral ceilings (see for example Holladay 2011) and some recommend against putting recessed can lights in any insulated ceiling (for example, Bailes 2011). Other alternatives are to install the recessed cans in an air-sealed dropped soffit or to limit use of recessed cans to only ceilings of rooms that have conditioned space above them such as a second floor. Another option is to avoid recessed can fixtures all together and use surface-mounted or pendant fixtures instead. LED surface-mounted kits that look similar to recessed can lights are now available.

How to Air Seal Recessed Can Lights in Insulated Ceilings

1. Choose fixtures that are labeled ICAT, meaning they are approved for insulation contact and are airtight as determined by the ASTM E 283 air leakage test.
2. Install according to the manufacturer’s instructions. Before installing the decorative trim, caulk the housing to the ceiling, or install the fixture using a manufacturer-supplied gasket (Figure 2).