Blower Door Testing

A blower door test is about the only practical way to determine the how "leaky" a house i

Gives some idea how bad your house is for air infiltration (how leaky it is)
Helps to locate air leaks so that they can be fixed.
Can be used to estimate heat loss due to air infiltration.

To do a blower door test, a powerful fan is installed in one of your entry door frames. All of the obvious leaks (windows etc.) are closed up or sealed up. The fan is turned on and blows air out of the house. The fan speed is turned up until the pressure difference between the inside and outside of the house is 50 Pascal (0.2 inches of water). The rate of flow through the fan is measured, and this is a direct indication of how tight your house is. The leakage at 50 pa will be much greater than your actual natural leakage rate (except maybe in a strong wind storm), but is its a standard value that allows you to compare your home to other homes.

The natural air infiltration rate will be (very roughly) 1/20th of the infiltration at 50 pa. For some sample homes:

Construction	ACH at 50 pa	Natural infiltration
Very tight new construction	Less than 1 ACH50
Typical new construction	5 to 8 ACH50
Older construction	10 to 20 ACH (or even worse)

Passive House Institute Standard	0.6 ACH50

For homes with a natural ACH of less than XX, the home should be ventilated with an HRV (Heat Recovery Ventilation) unit. This will provide the fresh air required by occupants and prevent odors and moisture problems. The HRV uses the heat in the exhaust air to heat the incoming cold ventilation air.

With the blower door fan running, a smoke pencil can be used to find air leaks, which can then be repaired.

References on Blower Door Testing:

From the Southface.org website

Blower Door Test Guide (50K pdf)

Infiltec (a maker of blower doors) has the detail on how to do a blower door test, and how to analyze the results:

http://www.infiltec.com/inf-btst.htm