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What Is a Blower Door?

By B. Turner
Updated May 17, 2024
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A blower door is a device used to detect air leaks in a home or building. Depending on how the building was constructed, it may include gaps and holes in its exterior that allow air to escape to the outdoors. To maximize energy efficiency, many homeowners attempt to seal as many of these leaks as possible to improve the airtightness of the structure.

Each blower door device features three basic components. A large plastic or wooden frame is placed into an exterior door frame within the building. This frame includes a specially-made cutout designed to hold a fan or blower. A pressure gauge connected to the blower allows operators to measure air pressure changes within the building and outside. During a blower door test, technicians use the blower to add or remove air within the home until a change in pressure has been detected between indoors and out.

Based on the volume of air that is needed to create a pressure differential, operators then determine how airtight the structure is. If a large volume of air must be added, this indicates that the home has lots of air leaks, which is linked to low energy efficiency. If only a small volume of air is required, the house is said to be tightly constructed, which is associated with high energy efficiency.

By evaluating the results of the blower door test, homeowners can then takes steps to improve energy efficiency. This may include adding insulation to walls, ceilings, and crawl space areas. It also includes caulking or sealing around pipe penetrations, or at any joints in siding or roofing. Seals around doors and windows can also help minimize air leaks. These steps not only help to cut heating and cooling bills, but also improve comfort and reduce consumption of fossil fuels like oil and natural gas.

After adding insulation and air sealing to the home, homeowners may repeat the blower door test to check for a change in air leak measurements. This device may also be used in a commercial setting to test the watertightness of windows, roofs, and other structures. A blower door test can also be used to test for positive air pressure conditions within a building, which are required by many fire codes. In commercial structures, the blower door may be applied to the building's heating, cooling, and ventilation ducts. These components are often subject to specific maximum air leak rates based on local building codes.

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Discussion Comments
By Soulfox — On Nov 24, 2014

@Markerrag -- I think you might be missing something, indeed. You are heading down the right path because a lot of people figure they need new weatherstripping and such when they feel a draft coming under a door or in a window. That draft will reveal large spaces where air can get through. Fill those spaces with something such as weather stripping or caulk and the problem is solved, right?

Now always. A lot of air leakage is on a small scale that can't readily be felt as drafts. Those smaller leaks can only be detected by something like a blower door.

In other words, the "it feels drafty" approach can help with large leaks, but some heavier artillery is needed for small ones. That's where specialized equipment is needed.

By Markerrag — On Nov 23, 2014

This sounds like a lot of trouble, doesn't it? Most human beings can tell if there is a draft coming through a door or a window. If there is, perhaps a new seal or some repair work should be considered.

You don't have to go through all of this blower door rigamarole to know if you have a drafty house.

Am I missing something or am I pretty much right?

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