Sealing Air Leaks in Your Home

Sealing air leaks can range from less than $100 to upwards of $1,000, depending on the job’s size and whether you do it yourself or hire a contractor.  Sealing your air leaks can cut your heating bills by hundreds of dollars a year in an older house.  Federal grants for sealing air leaks are available (an energy evaluation is required).	Doing it yourself involves leak detection and applying weather stripping, caulking and the like.	Sealing air leaks in an older house could reduce your greenhouse gas emissions by up to 0.5 tonnes a year.

Why should I seal the air leaks in my house?

Air leakage represents 25 to 40 per cent of the heat lost from an older home, costing hundreds of extra dollars in annual heating costs. Sealing those air leaks can be the most cost-effective repair you can make to such a house. Indeed, you should fix such air leaks and upgrade your insulation before investing in a high-efficiency furnace; otherwise, much of the heat it produces will simply escape from the house. A well-sealed house will also feel less drafty and help keep pollutants, insects and rodents out.

What are air leaks?

They occur when air enters and leaves the house unintentionally. They range from gaps under doors and around windows to foundation cracks and unsealed fixtures that penetrate attics. Individually, they may seem small, but they can add up to a hole big enough to crawl through.

When the building envelope is not well sealed, pressure differences build up, especially on cold and windy days, resulting in air leaking in at the bottom of the house and out at the top. While some air leakage locations are readily apparent, such as around windows and doors, other can only be detected using depressurizing equipment.  These can occur for example around exterior wall joints and interior partitions as well as other locations.

How can I tell if I need to seal air leaks in my house?

The most effective way is to get a professional energy evaluation. This should include a blower-door, or depressurization, test, which calculates the air tightness of a house and identifies air leaks. 

Signs of air leaks include abnormally high heating bills, drafty rooms – easier to feel on cold, windy days – and static electricity shocks from drier air entering the house in winter. You can do your own air-leak tests by holding a candle, lighter, incense stick or smoke pencil close to the edges of windows, external doors and baseboards, electrical outlets and light switches on outside walls. A more thorough examination involves going into the attic, investigating crawl spaces and checking out basement walls. The flickering candle test can be used here, too, but should be augmented by such things as checking, in the attic, for telltale signs of moisture and dirty insulation.

Where should I start?

The most cost-effective solution is to start sealing the largest holes, followed by sizable cracks and penetrations and then smaller leakages. Because large holes in, say, attics may be harder to identify, it sometimes makes sense to start with the obvious air leaks and then progress from there.

Some of the easiest air leakages to detect and fix are those around windows and doors. Caulking can easily be applied to cracks around window frames, doors and along the tops of baseboards, though in the latter case it may be worth first removing the baseboards and blocking the source of the leaks. Don’t forget to also caulk along cracks and gaps on the outside of the house.

A variety of weather stripping products are available for sealing leaks around outside doors. Most need to be cut to fit and then attached, either by self-adhesive glues or screws. Polyethylene foam, air-blocking gaskets are also easy to install behind light switch and electrical outlet plates on external walls.

To stop heated air loss up fireplace chimneys, insert an inflatable plug or a tight-fitting piece of rigid insulation below the damper; an attached cord makes them easy to remove when you have a fire. If the fire place is not being used, the chimney can be more permanently sealed off. Remember to REMOVE THE PLUG before starting a fire.

An inexpensive, easy alternative to replacing leaky windows is to apply self-adhesive, shrink-wrap film over the window and frame, using a hair dryer to create a tight seal. These films often provide a seasonal fix, applied at the start of winter over windows unlikely to be opened until spring.

What about the attic?

While air leaking into the attic doesn’t immediately escape to the outdoors, it represents precious heat lost, in winter, from your living quarters. The culprits here are unsealed penetrations from your living space into the attic – they include attic hatches, plumbing stacks, chimneys, kitchen and bathroom exhaust fans, recessed light fixtures and electrical wiring. These gaps can often be sealed with weather stripping, caulking, reflective foil insulation, expanding spray insulation, heavy polyethylene and high-temperature and acoustical caulking, though care must be taken around hot spots such as lights and chimneys. Insulation can also be added over open stud cavities above dropped-ceiling areas like kitchen cabinets and bathroom vanities, which can be big sources of air leaks. Needless to say, sealing air leaks in attics can be dirty work.

How about the basement?

One of the biggest potential sources of air leakage in a house is the fresh air intake for furnace combustion. In winter, this can provide a steady blast of cold air into the furnace room through the end of a 14-centimetre duct. While affixing a big ice cream bucket below the hole can help contain the leakage of this cold air, it’s much better to install a motorized combustion air damper, which only opens when the furnace is operating.

Similarly, it’s worth ensuring that the end of your clothes dryer vent has a flap and that it’s opening and closing properly; otherwise, cold outdoor air can leak in through your dryer. If necessary, a new flap can easily be installed. While you’re at it, apply some new latex caulking around the outside of the house where the dryer vent exits.

Floor drains with perforated covers are often a significant source of air leaks. Replacing it with a solid cover equipped with a trap will block these air leaks while still allowing water to drain if the basement floods.

The junction of floor framing and the foundation wall is often poorly sealed. Caulk around the sill plates and rim joists or place tight-fitting insulation in the space between the floor joists and then apply caulking.

Where can I find all the materials for air sealing my house?

Well-stocked hardware or home improvement stores should carry most of the materials and tools you need to do the job yourself. Some may also offer free or inexpensive do-it-yourself workshops on air sealing your house.

What if I don't want to seal these air leaks myself?

Air sealing specialists are not always readily found. Some insulation contractors, and some building contractors, will also seal air leaks; check the Yellow Pages. Get a quote first and ask what experience the contractor has undertaking such jobs.

If I thoroughly seal all the air leaks in my house, is there a danger of jeopardizing the air quality and having insufficient fresh air or combustion of things like fireplaces?

That is a possibility. Installing carbon monoxide detectors is a good idea. It’s also worth considering a heat recovery ventilator (also known as a heat exchanger), which allows fresh, filtered air to steadily flow through your house, while transferring heat from outgoing air to incoming air.