Drafts in your home that cause heat to escape during the winter can be a real drain not just on your comfort level, but on your wallet too. The leaks that cause them are not always easily detected, and are generally caused by problems in hard-to-reach places behind your walls. But that doesn’t mean you have to put up with them! Using a simple test, you can investigate the following common problem areas to see where your home is losing heat and costing you money.

Exterior Walls

Even in insulated homes, wetness, settling, or spotty installation can negatively affect the material’s ability to keep heat in. You can use something called a “blower door” test to check where in your exterior walls that insulation might have become compromised or be missing. To perform this test, you must first close all interior and exterior doors and windows in the house. Then, use a thick plastic sheet with a large fan embedded in it to cover one exterior door opening (the fan should be pointed outward). Blowing air outward through the door lowers pressure throughout the interior of the home, creating a vacuum. Outside air will be sucked inside through any gaps that may exist, revealing any leaks.

Once the blower door is up and running, temperature differences can be detected using an infrared camera. Large temperature differences—especially around ceilings, walls, or attics—can be indicative of a leak. For the best, most definitive results, you should perform the blower test when it is either extremely hot or extremely cold outside, because it is then that the temperature difference between the inside and outside of the house will be at its greatest. On an infrared camera, problem areas will appear black in the winter (where cold air is leaking in) and white in summer (where hot air is moving through the walls). These areas can tell you where insulation is missing or has failed.

If you find missing or failing insulation, what then? One solution is to drill small holes behind the siding and in the walls and then to blow loose cellulose through those. Another more expensive but more effective alternative is to use a slow-expanding urethane foam to seal joints and crevices where air is getting through.

Dodge The Draft, Save Money, Ensure Comfort!

Eaves, Knee Walls, and Attics

On your infrared camera, you may notice a lot of leaks in places where framing comes together, like cantilevers, attics, eaves, and knee walls (the short walls that support your rafters). These places often lack enough insulation, or have insulation that was not installed correctly. As a result, these can be the sites of some of a building’s greatest losses of heat.

How do you prevent this? For knee walls and eaves, the best solution is to use expanding foam. In attics, the answer can depend on a few things. If your HVAC system is located in your attic, it is best to coat the underside of the roof sheathing with insulation. If not, it is usually enough to just seal the attic floor using something like blown-in cellulose. If either of these options is too expensive, addressing the gaps in the framing with a combination of rigid boards, blown-in cellulose, and expanding foam can often make sure that the insulation and air barrier work together to keep heat in.


Windows are another common site of leaks, and can be responsible for 10 to 25% of a home’s heat loss. Instead of thin glass being to blame for temperature differences, most of the leaks occurs below sills and through headers, which are not commonly well-insulated. While this should be visible on the infrared camera, a smoke stick can help you pinpoint the exact location of these small drafts. Smoke sticks are about the size of a candle and, when squeezed, emit a nontoxic white powder that looks like smoke. To find the offending leak, hold one up alongside a window casing and see where the smoke goes.

So what next? You could always replace your windows, or you could seal the existing ones. In places where insulation is insufficient or missing, drill a series of holes around the inside of the jamb all the way around the window, then inject them with expanding foam.

Dodge The Draft, Save Money, Ensure Comfort!

Plumbing and Wiring

Smoke sticks don’t just come in handy when it comes to windows—they also are useful for examining where plumbing chases or wiring cut through ceilings, floors, or walls. Ceilings especially are especially notorious offenders when it comes to letting outside air get inside and letting conditioned air leak into the attic. Use your smoke stick to check for trouble spots around radiator pipes and light fixtures. Seal around these areas with caulk or canned foam insulation.