, Newburyport, MA


February 28, 2012

Plugging heat loss caused by recessed lights

I conducted two audits recently that warrant another discussion of recessed lights and the important role they have in heat loss and dollars wasted. The first was an audit in a North Shore suburban home in which the new homeowners had six recessed lights installed in the living room within months of moving in. Being a Cape, the attic is directly above the first-floor ceiling. In essence, what the new homeowners did to create a pleasant ambiance was punch six holes in their ceiling. The electrician did not serve them well, but rather installed non-air-tight and non-insulation-contact fixtures. And he had to pull the insulation away more than 3 inches from each light for code compliance with this type of fixture. Result: a total area open to the attic of about 6 square inches and heated air leaking out.

The second audit that I did at another North Shore residence, a Colonial built in 2003, had 18 recessed lights on the second floor adjacent to the attic. These were all insulation-contact-rated fixtures (a good start) and had 10 inches of Fiberglas over them, but they were not air-tight. We energy nerds are always telling folks that Fiberglas does little to stop air movement and is effective to its rated R-value only when it is enclosed on all six sides.

So, 10 inches of Fiberglas batt insulation, which is assumed to be about R-30 (and I am being generous), is effectively about R-20 (and I am being generous again). Not only is heated air being pumped through the recessed lights, but the gaps between the Fiberglas and the drywall due to strapping and the gaps between the batts and the floor joists are all causing convective air currents that help to drop the R-value like a lead balloon. Result: a total area open to the attic of about 1.5 square feet, heated air leaking out and reduced average R-value across the attic floor.

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