Air leakage occurs when outside air infiltrates the home through unintended openings in the building envelope. This constant exchange of air causes discomfort, leading to cold spots in winter and warm areas in summer. Addressing these leaks improves the consistency of indoor temperatures and reduces the workload on heating and cooling systems. Sealing these gaps significantly lowers energy consumption and utility bills, making the home more efficient and comfortable year-round.
How to Find the Hidden Air Leaks
Identifying the exact location of air leaks is the first step in effective air-sealing. While large gaps are obvious, the most significant energy loss often comes from numerous small, hidden cracks. A simple detection method is the “smoke test,” which uses a lit incense stick or a smoke pen.
To perform this test, first depressurize the house to exaggerate the airflow. Close all windows and exterior doors, turn off combustion appliances, and run exhaust fans like the kitchen hood or bathroom fans. Once the house is depressurized, slowly move the smoking incense stick around the perimeter of suspected leak areas, such as window frames, door casings, and exterior electrical outlets.
If the smoke stream moves horizontally, is sucked inward, or is blown outward, it indicates an active air leak. This method pinpoints leaks too small to feel by hand. For a more comprehensive assessment, a professional home energy audit uses specialized equipment like a blower door to quantify the total air leakage in the structure.
Sealing the Most Common Culprits: Windows and Doors
Windows and doors are common sources of air infiltration. Sealing these areas involves a combination of materials to address both the stationary frame and the moving sash or door. For gaps between the frame and the wall, apply exterior-grade caulk, such as silicone or polyurethane, to create a permanent, weather-resistant seal.
For moving parts, weatherstripping is used. Options include adhesive-backed foam tape, EPDM rubber, or V-strips (tension seals). V-strips are effective for sealing the sides of double-hung windows and door jambs. For the bottom of exterior doors, a door sweep or bottom seal closes the gap between the door and the threshold.
A temporary solution for drafty windows is the heat-shrink plastic film kit. This process involves applying double-sided tape around the interior window frame, stretching the clear plastic film over the tape, and then using a hairdryer to heat and shrink the film. The resulting taut membrane creates an insulating air pocket that reduces air infiltration and heat transfer.
Stopping Drafts Through Walls: Outlets, Vents, and Fixtures
Small penetrations through the wall collectively contribute a significant amount of air leakage. Electrical outlets and light switches on exterior walls are examples, as the box cavity provides a direct path for outside air. A simple fix is to install pre-cut foam gaskets directly behind the cover plates of these fixtures.
Before working on any electrical outlet or switch, turn off the power at the circuit breaker for safety. Once the cover plate is removed, place the foam gasket over the device and reattach the cover plate, creating a seal against the wall surface. For gaps between the electrical box and the drywall, apply a small bead of caulk or minimal-expansion foam sealant to stop air from bypassing the box.
Utility penetrations, such as where plumbing pipes, cable lines, or dryer vents pass through the exterior wall, require sealing. Small gaps can be filled with caulk, while larger voids should be sealed with low-expansion spray foam. Using minimal-expansion foam prevents the material from deforming the pipe or the surrounding wall structure as it cures.
Tackling Major Structural Leaks: Attic and Foundation
The largest air leaks are often found where the living space meets unconditioned areas, such as the attic and the foundation. This is due to the “stack effect,” where warm air rises and escapes through the attic, pulling cold air in from the lower levels. The attic hatch or pull-down stairs represent a large, unsealed hole in the ceiling.
To seal the attic access, apply weatherstripping to the perimeter of the hatch opening to create an airtight seal. The hatch cover should also be insulated by attaching rigid foam board to the attic-facing side to reduce heat transfer. For pull-down stairs, an insulated box cover can be placed over the opening to seal and insulate the assembly.
In the attic, penetrations through the ceiling, such as plumbing vent pipes, electrical wiring, and recessed light fixtures, must be sealed. For penetrations near a heat source, use a fire-rated caulk or foam to maintain fire safety. At the foundation level, the rim joist—the perimeter of the floor framing where it rests on the foundation—is a major source of air leakage. Seal the rim joist with rigid foam board and spray foam or a two-part spray foam kit.
Long-Term Strategy: Professional Audits and Insulation
After completing DIY air-sealing projects, a professional home energy audit can analyze the remaining air leakage. This audit includes a blower door test, where a powerful fan is mounted in an exterior doorway to depressurize the house. This process makes it easier to locate smaller leaks missed during the initial inspection, often using a smoke pencil to visualize the airflow.
The data from the blower door test quantifies the home’s air tightness, allowing for targeted sealing work. Air sealing must be completed before adding insulation, as insulation alone does not stop air movement. Air flowing through insulation significantly reduces its effectiveness. Once the air barrier is complete, upgrading the attic and wall insulation is the final step to reduce heat loss and maintain a consistent indoor temperature.