B8. Control Air Leakage

Description

Air leakage through holes, gaps, cracks, penetrations, and electrical receptacles is a major source of heat loss from a dwelling unit. Controlling this air leakage through a combination of weatherstripping and strategic sealing can significantly reduce the amount of heat lost to the outside, thus reducing the amount of energy needed to heat the dwelling unit. Insulation also can help reduce air leakage. In addition to saving energy, controlling air leakage can reduce moisture problems and reduce the influx of odors and contaminated air from the basement and other units, while increasing the overall comfort of the residents.

But reducing air leakage through air-sealing techniques is more complicated than simply weatherstripping and caulking. Two important principles must be understood.

First, even if a building is full of holes, air will not move through those holes unless there is a difference in pressure between indoors and outdoors. This pressure differential depends on the difference between indoor and outdoor temperatures, wind speed and direction, and mechanical ventilation. If there is no pressure differential, the air stands still and does not leak in or out. This is important because sealing a hole where there is no pressure differential will not save energy. Pressure tends to be highest on upper and lower floors and in basements. In the heating season, hot air rises and pushes on the ceiling, creating high positive pressure and eventually leaking out. When it does leak out, it is replaced by cold air coming into the lower part of a building, where the pressure is negative from all the warm air moving upward. This force is called the “stack effect.”

The second important principle is that air sealing can affect air quality. Air leakage is the primary source of ventilation in many buildings. Tightening a building by reducing air leakage can endanger the health of the occupants in buildings with no mechanical ventilation. This risk is highest in buildings with significant sources of indoor air pollution, such as backdrafting from gas appliances or high occupancy levels. If a building does not have mechanical ventilation, it is recommended that a ventilation system be installed before any significant air leakage is significantly reduced.

Applicability

• Single-family and multifamily buildings

Types

• Weatherstripping
  • window type
  • door type
  • rubber
  • plastic
  • metal
• Air sealing
  • caulk
  • gaskets
  • insulation

Considerations

• Air sealing should be performed in conjunction with an assessment of the building’s ventilation system to assure adequate air quality. Measures to reduce air leakage reduction are best performed by an experienced professional.
• Weatherstripping should be selected for quality and durability.
• The technician should check combustion appliances (such as gas-fired heaters and water heaters) before and after air sealing to ensure that they are venting properly.

Performance/Economics

• Air sealing, on average, can reduce energy usage by 153 therms or 1330 kWh annually, or approximately 25 to 40 percent.

Resources/Links

Energy Conservation for Housing – A Workbook, HUD, September 1998. Pages 7-37 through 7-39 address air infiltration and leakage.

Improving Energy Efficiency in Apartment Buildings, American Council for an Energy-Efficient Economy, 1995. ISBN 0-918249-23-6. Pages 98 through 103 address infiltration and air leakage measures in apartment buildings. 

Consumer Guide to Home Energy Savings, American Council for an Energy Efficient Economy, 1999, ISBN 0-918249-38-4. Pages 11 through 17 address strategies to control air leakage.

Insulation and Air Sealing. Part of the U.S. Department of Energy's Consumer Guide. Discusses both air leakage and moisture control.