Seal Air Leaks to Cut Home Energy Costs

These easy, inexpensive methods for sealing air leaks could save you a bundle on your home energy costs.

| October/November 2010

air leaks, home energy costs

Applying caulk around windows lowers home energy costs by stopping air leaks, which otherwise allow heat to escape in the winter.


Air leaks cost us dearly. According to the Energy Star program, most people could save about 20 percent on their heating and cooling costs by sealing up air leaks. Most older homes are riddled with holes in the “building envelope,” which is made up of the outside walls, roof and foundation. These leaks range from large, obvious holes — such as broken or missing windowpanes in the basement — to tiny, almost invisible cracks. Small cracks can have a big impact. An eighth-inch-wide, 6-foot-long crack between a door and a doorjamb, for example, is equivalent to a 9-square-inch opening!

On cold winter days, leaks in the building envelope let heated air escape and cold air enter. In the summer, cool air slips out and hot air seeps in. Air leaks also allow moisture to enter walls and ceilings, which may make them breeding grounds for mold. Eventually, water in walls may lead to structural damage, because framing, if constantly wet, begins to rot. Replacing rotted framing is expensive, as a neighbor of mine recently discovered. He found moisture damage in his home’s framing members, and fixing the mess cost him a whopping $125,000! Sealing air leaks not only lowers home energy costs, it leads to a healthier, more durable home. And as home improvement projects go, this one is amazingly easy and inexpensive.

Find Those Air Leaks!

To seal air leaks, you first need to identify them, either on your own or with the help of a professional energy auditor. To identify leaks yourself, begin by looking for large openings in outside walls, then search for smaller, less visible openings. On windy days, you can find these leaks by feeling around doors and window frames, at the base of walls, and anywhere else with an opening from outside to inside walls. You can also detect leaks with a stick of burning incense — air leaking into a home will deflect the smoke. Be sure to check around electrical outlets and light switches (even those on interior walls.) Ceiling fixtures — especially recessed lighting and wholehouse fans — are other major sources of heat loss in the winter.

After you’ve found the air leaks in your home, you can hire a professional retrofitter to seal them, or you can do the work yourself. If you choose the latter, you’ll need some inexpensive supplies and simple tools, including clean rags, rubbing alcohol, a caulk gun, clear or paintable caulk, liquid spray foam (expanding foam), weatherstripping, foam gaskets for sockets and light switches, a utility knife or scissors, a screwdriver, and a stepladder.

Start in the Basement

Basements are a major source of air leaks, so they’re a good place to start. Begin by sealing the largest and most visible cracks in your basement or crawl space. Replace any broken or missing windowpanes, or install rigid foam insulation over the openings. Seal any gaps — such as those around dryer vent exhausts — with caulk or expandable liquid foam, which we’ll discuss shortly.

Next, seal cracks between the top of the foundation and the wall. These are often so large that light shines through them. Turn off the basement lights and look at the walls from inside to locate gaps, then seal them with caulk or foam. You can usually seal cracks from inside, though some may be easier to access from outside. This is also a good time to insulate the cavity formed by the floor joists and the rim joist. Place batt or blanket insulation in the cavity, or use rigid board insulation, which can be cut to size and friction-fit into the space. Another option is to use expanding foam insulation.

Linsey Vandrick
12/3/2010 5:15:20 PM

While sealing air leaks to save energy and money on heating bills is admirable, I was disappointed to see this article listed under the designation of "green home improvement." Have latex, foam and silicon passed into the realm of "green" building products? The advice given in this article is the same you would find in any mainstream home improvement book or energy saving guide. I would like to see Mother offer truly "green" alternatives to plastics-based caulking, insulation, and weatherstripping in upcoming issues, or provide links to resources that contain this information. Thanks!

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