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Blower Door Test

What is a Blower Door Test?

When either insulating a new home or upgrading (retrofitting)  the existing insulation, a blower door test can determine the effectiveness of the quality of air sealing and insulation process. Before the new construction insulation is done, a quality insulation contractor will do a thorough air seal of all the gaps and cracks in the walls of the home including the penetration points. Anywhere two framing members are joined together, i.e. the wall studs, the top plate, the bottom plate etc… get caulked and then the windows and doors get sealed with low expanding foam so that it doesn’t harm the warranty or performance of the windows.

A blower door test is performed when a shroud is installed in a door with a fan. The fan pulls air out of the house to simulate air infiltration into the home. The exterior doors and windows are closed. The exhaust fans are turned off. The HVAC is turned off and the interior doors are left open. And the combustion appliances are turned off and closed. At this point the home is ready for testing

Air sealing is also done in the attic after drywall before the insulation is installed. All of the places where the wires pertrude through the attic or the plumbing, HVAC, or anywhere there is an openinginto a wall cavity or stairwell. Those are foamed with a fire retardant foam. Larger areas will be sealed of with 6 mil plastic and caulk to block the airflow and hold the insulation.

After all this is done, a blower door test can be conducted to determine the A.C.H. (air changes per hour). A.C.H. is a determination of how much air infiltration is leaking into the house every hour. That is how many times the air has to be re-heated or cooled again every hour to maintain the consistent temperature. The more A.C.H, the more money it costs to heat and cool the home.

The test is conducted at 50 pascals of pressure. One pascal is the amount of suction through a tube that it takes to lift the weight of a postage stamp. 50 pascals simulates the significance of a typical weather storm to create that amount of air infiltration.


Existing homes do not have the luxury of sealing all of those cavities in the walls. Though some air sealing can be done where the floor meets the trim, the top of the trim, the window frame, the window trim, and any penetrations coming through the wall.


The existing attics typically have existing insulation that prohibits the loacating and sealing of the attic penetrations. In those cases, the existing insulation is removed and then the penetration points are hunted and sealed.


Fiberglass insulation is like a filter and allows air to flow right through it. This includes the heated and cooled air. It is definitely a smart choice to remove the existing fiberglass from the attic so that the proper and thorough air seal can be done. When there is fiberglass in the existing walls, an exterior or interior dense pack is done. This is when siding is removed, or holes a drilled in the drywall inside, and a tube is injected into the entire wall cavity to dense pack cellulose at 3.5 pounds per square food to achieve the reduction of air flow. In this case the existing wall insulation is collapsed to almost nothing and filling the cavity with a dense packed cellulose. This greatly reduces the A.C.H and over all blower door number.

In existing homes, a blower door test can be done before and after the work is compleded to determind an A.C.H. reduction. Which shows how much air leakage was reduced and showing the success of the project

Once the Blower door test is completed, a determination can be made if more air sealing is needed.

Some ask if a house can be to air sealed, or too tight. The answer is yes, however, the 1.5 A.C.H of a typical cellulose home is well above that. This means the home is very healthy regarding air quality and not too much where it is too costly to heat and cool the home.

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