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Air Sealing

What is Air Sealing and How can it Save Energy?

Air leaks out of your home occurs when the air pressure inside the home is greater than the air pressure outside the home –Inside of the house means the part of the house you are using as living space (conditioned space). Outside of the house -the part of the house you are not leaving in, like car garage, attic, basement (unconditioned space) and exterior. Air also travels from hot to cold. The bigger the hole and the greater the pressure or temperature difference, the greater the air leaks number is.

Quick Facts...

Uncomfortable drafts, interior high humidity levels, and high energy bills are often the result of air leaks. Air sealing is the first step in making your home more energy efficient and comfortable.

It is not uncommon for small air leaks to add up to a window size opening in the home, which is open 24/7 throughout the year.

Sealing air leaks while preparing for adequate ventilation is the first step to having an energy-efficient, healthy home. According to U.S. Department of Energy (U.S. DOE) studies, air sealing can often achieve home energy savings of 10% to 20% and even more in older, leaky homes. In addition, air leakage is a leading cause of moisture damage in otherwise well-insulated homes.

So where those holes comes from?

For homes made out of wood frames, they are a living thing. They breathe, they span and they shrink through the seasons, but more importantly, as lumber dries it will shrink even more, and in some cases, warp. So a not so bad framing –air leaking speaking, can become extremely leaky five to ten years down the road. Other larger penetrations were made in your home by a variety of well meaning contractors that had no idea about energy savings procedures. The Plumber cut a bunch of holes for pipes and the electrician cut a bundle of holes for wiring. The Heating Contractor cut a number of holes for ducts and flues and the window and door contractor cut some huge holes for windows and doors. Part of the air sealing procedures is to play detective by following around the path the plumber, electrician, HVAC, and other professionals took as they were doing their jobs, sealing up all the holes they left all over the place.

Goal of Air Sealing

The goal of sealing cracks and gaps is to prevent unwanted air from flowing both into and out of the home. For example, a gap between a door and the door frame could let heat escape in winter and heat enter the home in summer. Furnaces or air conditioners have to work harder to make up for lost heat (winter) or unwanted heat (summer).

Air gaps in the building shell may also feel uncomfortable from the different cold /hot areas in your home. Cracks and gaps in the tops and bottoms of homes are also significant sources of energy loss because as hot air naturally rises it escapes through gaps in ceilings. When this occurs, cold air will be pulled in through gaps in our floors, making us even colder in winter (the ‘stack effect’).

The ultimate goal of air sealing is to reduce both physical discomfort and energy use. Air sealing is a most before adding insulation to a home. Most types of insulation, aside from foam insulation, will let air pass through them. In addition, once insulation is added it is more difficult to uncover and plug air leaks hidden underneath the insulation.

What is Stack Effect?

Stack Effect is a natural force that drives air leakage. Warm air is less dense than cold air, so warm air rises and cool air replaces it. Stack effect takes place 24 hours a day, 7 days a week. Cooler air enters the home through holes and penetrations from the low points of your house –crawlspace and basement. As it rises through your home it takes your precious “conditioned” air –which in Winter would be hot air mixed with humidity. The now warmed air leaves your home by passing through the holes and penetrations in the ceiling, attic, roof but leaving behind the moisture taken from your home on the plywood. This excess moisture accumulation can cause rot in the wood and or mold. .

Hidden Air Leaks:

Air leaks can be found in a number of places throughout the home and although you find the more obvious air leaks, the difficult task is to find those hiding in your basement, crawl space, knee wall, and or attic. Those hidden penetrations are the ones that dominate the air leakage. Have you ever felt cold air coming through an outlet of an interior wall? Crazy right? But that is an hidding air leak that needs to be taking care of.


Windows and doors are only a small portions of the air infiltration story for average homes in the U.S. because each home has been built differently, on different locations, like some may be surrounded by trees which can slow down the stress of the winds and others no trees at all. It is important that we investigate your home thoroughly so we can determine the most cost effective ways to air seal. During the auditor’s blower door test, parts of the home with high rates of air exchange can be identified. Similarly, leaks in a home’s ductwork can be identified using a duct blaster.

Floors, walls and ceilings /attic= 31% combined

Plumbing, electrical and HVAC penetrations= 17%

Ducts= 15%

Fireplaces= 14%

Doors= 10%


Electrical outlets= 2%

So how we find those hidden leaks

One of the steps we use during our energy audit is to figure out the total amount of air that is leaking from your home. We use a large fan, which we called a blower door, and we set it up at one of your exterior doors. This device pressurizes the house to pretend a standard 20 to 25 miles an hour winds that is pretty common your house to get in those winter months. With the house now pressurized, our equipment will provide us data on the amount of air leakage that occurs as a result of air leaks. The leakage is represented in cubic feet of air per minute, CFM.  A cubic foot of air is about the size of a basketball.

Important thing you should know!

There is a huge green van wagon of companies out there that they are trying to make a sell under the green flag. Window replacement companies are one of them but the thing you should know is that windows replacement are the most expensive investment on your home with the least energy savings. But wait, it gets worse! Your original windows were certainly installed without any air sealing procedures, when the replacement window only takes the old window panes out, leaving in place the original old wood window frame, you now have a very sophisticated double or even a triple glass window on a very leaky wood frame, not providing you with any of the energy savings you were promised. If you have a single glass window, or a damaged window, and you feel it should be replaced, I would suggest that you get it replaced with a “new construction” type window, which means that the entirety of the window is removed exposing the house frame, so air sealing can be part of the installation of the new window.  

Air sealing is also something you do before you install additional insulation in the attic and before you install that new high efficiency furnace or boiler, otherwise you are heating the exterior of your home very efficiently!  Air sealing is something you do after the Home Energy Auditor tells you that the blower door indicates there is 3,814 cubic feet of air leaking into and out of your home every minute.

Windows and doors

The most cost effective measure to save energy from leaky windows and doors is by professionally removing the interior wood trim of the units and applying non-expanding foam in the cavity.  Weather stripping should also be installed and/or replaced as necessary around the entire door frame interior. A door sweep attached to the bottom of a door and a properly fitted threshold attached to the bottom of the door frame can also reduce air infiltration.

In Summary:

Air sealing is an imperative step in making a home more energy efficient and comfortable. A blower door test will indicate how much air sealing is necessary, and the energy audit will also determine if your home needs mechanical. The audit itself is also the best way to detect specific air leaks. For homes with air exchange rates less than 0.35 ach or if homeowners want to maximize energy conservation, and completely control the quality of the air you breathe by sealing a home completely, the installation of a heat or energy recovery ventilator is needed.