A home is like a tent, where the parts of the exterior shell “walls, windows, doors, siding, foundation, and roofing” are designed to protect against the elements. By and large these construction features are very effective against cold, heat, wind, and moisture. There’s a big difference, though, between a tent and a house. Whining mosquitoes and rain-soaked sleeping bags, for example, alert a tent’s inhabitants of a hole in its fabric. In a house, however, signs of air leaks are more subtle. They are usually so small that they cannot be seen with an untrained eye.

Even the smallest of air leaks in a house can create big problems. When outside air leaks into homes, it can create drafty rooms or make a home feel dry during cold winter months. When inside air leaks to the outside, it takes with it cooled air in summer and heated, moist air in winter. This causes homeowners to pay more in utility costs to keep indoor air at the right temperature. It also unnecessarily increases the amount of greenhouse gases released into the atmosphere as more natural gas and coal are burned to power homes’ heating and cooling systems.

Home air leaks commonly occur in window and door openings, along interior wood trim, and where utility connections, such as electrical service, enter foundation walls. Air leaks can also occur in unseen areas of the attic where it is penetrated by light fixtures, plumbing stacks, and access hatches. Despite their tiny individual size, the total area of the cracks and crevices in a home’s exterior can add up to the size of an open window!

You wouldn’t camp in a leaky tent, and you shouldn’t live in a leaky house. Air sealing plugs the holes in a home so that inside air stays at the temperature you desire using the least amount of energy.

How to find and seal air leaks

Most air leaks occur in predictable locations. Homeowners can identify leaks themselves, but others are more easily located by experts using special diagnostic tools. Fix the holes you can crawl through first, the ones you can stick your hand through second, and the little ones last.

1. Some air leaks can be felt by running a damp hand to feel for a breeze along window, door, and baseboard trim. These linear leaks are easy to fill with silicone caulk. Exterior doors can be sealed using air-stopping sweeps along their bottom edges, plus weather stripping products that create a leak-proof cushion between the door frame and the door itself. Weather stripping is also available for windows.

2. Look for cobwebs in or near basement foundation penetrations. If the webs are blowing you know that air is leaking. Buy a can of foam sealant from the hardware store, and fill the cracks following manufacturer’s instructions.

3. Attic leaks are a bit more complicated. If you are comfortable climbing into your attic, then look for and seal around electrical penetrations at the top of interior walls, seal around plumbing stacks and around the chimney, and caulk around the tops of interior walls where the top plate meets the plaster or drywall.

Can you seal too much?

The NEC’s motto is, “Seal it tight, but ventilate it right.” Most minor do-it-yourself air sealing will not lead to any problems. A more complete air sealing job, however, can change the dynamics of your home so that the pollution created by combustion appliances (gas and oil furnaces, water heaters, dryers, and kitchen ranges) creates indoor air quality hazards. Depending on the level of sealing you plan to perform, start your project with an informational energy audit from your utility company and work with a qualified air sealing contractor that has the tools to find, fix, and test your home’s performance after the job is complete. Homes that are sealed tight will benefit from mechanical ventilation, from simple measures such as fans in bathroom and kitchen walls, to whole house air handling systems.