The Department of Energy estimates that up to 30% to 40% of energy loss in a house can be attributable to air infiltration. Air-sealing is the process of “plugging the holes” to stop the convective heat losses. Most houses are insulated using fiberglass while some of the older houses have nothing at all. While fiberglass is a thermal barrier, it is not an air barrier and therefore loses a lot of its insulation value due to air movement within the wall. Stopping air infiltration is the first defense against energy loss. Various materials are used to fill the cracks, crevasses, holes and larger by-passes to stop the flow of air out of the house. The most important areas are the basement and attic. In the basement it’s very important to seal and insulate the rim/band joist that sits on top of the foundation and goes around the entire perimeter of the house. In the attic, by-passes such as the access hatch, pipe and vent penetrations, flue and chimney chases and wall top plates have to sealed. Without this work, warm moist air from inside can filter out through the fiberglass and condense on the cold outer surface of the house. This condensation can eventually lead mold and mildew problems and cause structural damage.

The best option is to “Build Tight and Ventilate Right”, in other words, seal the house up as much as possible and then install a ERV (Energy Recovery Ventilator) with a HEPA filter to bring in the fresh air, condition it and filter it.

How Does the Air Escape? Air infiltrates into and out of your home through every hole and crack. About one-third of this air infiltrates through openings in your ceilings, walls, and floors.

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Sources of Air Leaks in Your Home Areas that leak air into and out of your home cost you lots of money. Check the areas listed below.
1. Dropped ceiling
2. Recessed light
3. Attic entrance
4. Sill plates
5. Water and furnace flues
6. All ducts
7. Door frames
8. Chimney flashing
9. Window frames
10. Electrical outlets and switches
11. Plumbing and utility access

See these DOE articles on Sealing Air Leaks and Air Sealing.