Air Leaks

Sometimes these are large enough that you can see daylight coming through, for example, around a door or window. More common, however, are the small gaps that you can’t see — in basement walls, through insulation where electrical boxes have been installed, or in the attic. If you add up all the leaks found in a typical home, you’ll get an opening the size of a basketball. What a waste — that’s like leaving a window wide open in the cold of winter!

Sealing air leaks will improve the comfort in your home, and can also help save money on your energy bill, especially since heating and cooling costs are responsible for half of a home’s utility expenses. When warm air leaks out of a home, more energy must be used to heat the cooler air coming in. By sealing air leaks, households reduce the amount of energy they use to heat and cool their home, and thus lower their utility bill. Using less energy also means a smaller carbon footprint if the home is heated using fossil fuels which release carbon dioxide when burned for energy. This is an important step toward becoming a net zero home.

Where do most air leaks occur?

The most prominent air leaks in a home are typically in the attic and basement. This is due in part to the stack effect. Warm air in a home rises because it is less dense than cool air, and pushes up against the top of a home, increasing pressure in the attic area. As air has left the basement, a negative pressure is created, which creates a vacuum effect which draws in cold air from the outside. This cold air must be warmed up, using additional energy, only to have the warmer air rise up through the house and exit through gaps in the attic. The image on the right illustrates common areas for air leaks.

The protection against air leaks is an air barrier. An airtight home retains heat within the building envelope — the boundary between the inside of a home and the outside. The building envelope, which is also sometimes referred to as the building thermal enclosure, determines where you want to seal your air leaks and have your insulation. The image above contains an inset illustrating the home’s thermal envelope in red. Are all parts of the home inside the building envelope?

Finding air leaks with AN ENERGY AUDIT

While you may be able to detect some air leaks visually or by running your hand over the surface of walls, you can get a much more precise measurement through an energy audit. During an energy audit, the contractor will often conduct a blower door test. A blower door test uses a giant fan to pull air out of your home. It then measures how much air, usually in cubic feet per minute at 50 pascals of pressure (CFM50), is sucked out by the fan, which indicates the extent to which your home is air tight. To visualize the CFM50 units, think of a cube with sides that each measure a foot. The CFM50 measurement is the number of these cubes of air that the fan used in the blower door test can suck out of your house in a minute at that pressure.

While this may give us some indication of how leaky your home is, the measurement will vary widely based on the house’s size. To better compare the leakiness of one home to another we can convert this to a measurement that takes the size of the house into account. To do this, we think about how quickly the volume of air that exists in the space of your house can be replaced over a period of time. This measurement is Air Changes per Hour at 50 pascals of pressure (ACH50). CFM50 can be converted to ACH50 by multiplying it times 60 (to convert from minutes to an hour) and divided the result by the volume of the home (in cubic feet): ACH50 = (CFM50 x 60)/Volume of home. Many energy audit reports will provide this figure to you, but in some cases you may have to calculate it.

With the ACH50 measurement, we can now compare our home to others. The current New York State residential code requires new homes to have air leakage no greater than 3 ACH50 (this article gives a good visual on what 3 ACH50 looks like), but most older homes are measured to have greater than 9 ACH50, and many locally even have much higher measurements! We recommend that all homes aim for at least 7 ACH50, what is labeled “Good” in the table below.

We strongly encourage getting an energy audit, which are free for all NY State residents, in which professional clean energy contractors can help find the major areas of air leakage and identify comprehensive solutions. The Get Your GreenBack website has a list of local contractors that you can contact for a home energy audit, and programs you may be eligible for that can cover part or all of the cost of suggested improvements.

There are financial incentives for everyone, and low-income households can access programs that cover over $10,000 in air sealing and insulation improvements.

DIY Solutions

While comprehensive air sealing and insulation work is best done with professionals, there are a number of DIY solutions for sealing air leaks. Two of the most common, inexpensive, and simple options are caulking and weather stripping. Caulking involves using a flexible material to seal cracks, gaps, or joints that leak air in your home. There are different types of caulk that can be found at local hardware stores. Ask store employees for recommendations on the best material for different spots in your home.

Weather stripping is primarily used to seal air leaks around movable building components, such as doors or operable windows. Materials used to weather strip vary in cost and effectiveness, and can be found at local hardware stores where you can get recommendations for which ones are best for your situation.

In addition to weather stripping and caulking, you can also install foam gaskets on light switches and outlets. Outlet gaskets, which are also referred to as outlet sealers or outlet insulators, can be purchased at local hardware stores for easy insulation. Attaching plastic sheets over your windows is also a relatively easy and inexpensive way to reduce heat loss. The following video shows three simple DIY actions to reduce air leaks in your homes.

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