There’s a 10-second fix for the most surprising offender: recessed lights.
Insulate Around Recessed Lights
Out of all the possible air leakage sites in a house, recessed lights, also called can lights, cause the worst leakage. The Pennsylvania Housing Research/Resource Center found this fact as part of an inspection protocol involving blower door testing and infrared imaging.
Plug Open Stud Cavities
Most of your house probably has an inner skin of drywall or plaster between living space and unheated areas. But builders in the past often skipped this cover behind knee walls (partial-height walls where the roof angles down into the top floor), above dropped ceilings or soffits, and above angled ceilings over stairs.
Close Gaps Around Flues and Chimneys
Building codes require that wood framing be kept at least one inch from metal flues and two inches from brick chimneys. But that creates gaps where air can flow through.
Weatherstrip the Attic Access Door
A quarter-inch gap around pull-down attic stairs or an attic hatch lets through the same amount of air as a bedroom’s heating duct. Seal it by caulking between the stair frame and the rough opening, or by installing foam weatherstripping around the perimeter of the hatch opening.