Blower Door and Air Duct Testing
What is a blower door?
A blower door is pretty much what it sounds like. It consists of an adjustable frame fitted with a membrane that inserted in an exterior
door frame. This assembly has a large hole near the bottom that a high velocity fan is inserted and an electronic instrument call a
manometer is used to measure the air leakage or "tightness" of the house envelope. The fan has an adjustable control to increase
and decrease the fan speed and flow and the manometer takes air flow measurements to determine if the house is leaky, average
How is the blower door set up?
Before the testing begins, all windows need to be closed, fireplace dampers need to be closed and if there are any gas appliances
present within the house envelope, the pilot lights need to be extinguished. The technician then will begin the testing by either
de-pressurizing the house with the fan blowing to the outside or pressurizing the house with the fan blowing to the interior. The fan is
turned up to a pressure value that is equivalent to a 20mph wind blowing on all side of the house. This value is small and will not
cause damage to the house or belongings. When this pressure value is reached, the manometer will indicate how much air is
leaking from all the cracks and openings from the house.
What if my house is found to be leaky?
All homes have air leaks in some form. In fact, some new homes are so "tight" they have to have fresh air devices installed. You can
have a home too tight and need a certain amount of fresh air exchanges so that the air does not become stagnant. But if your home
is found to be very leaky, air sealing should be performed. An average house can have enough air leaks that if you added them up, it
would be like having a small window open all the time. To find where these leaks are, a smoke or powder generating device can be
used to go throughout the house and locate these so that you know where sealing should be performed.
I personally prefer to de-pressurize the house to determine the leakage and then pressurize the house to find the leaks.
An important consideration before air sealing a home with gas appliances is to have the appliances checked for proper drafting
and emission of carbon monoxide (CO). I include this as part of the blower door and air duct testing. To read my article on
Why test the air ducts?
The majority of the air loss from air circulating in the heating and air conditioning system is from the joints and connections in the air
ducts. To test for leaky air ducts, I use a device called a pressure pan. While the blower door is running, the manometer is
connected to the pressure pan and is placed over each air register and return to determine if they are leaky or tight. If they are found
to be leaky, the best method to seal ducts and joints is with a thick gray substance called mastic. This can be purchased from any
hardware store and is applied with a brush and when it dries, it seals the air leaks like a cast.
See the video below for a demonstration of a pressure pan test. Keep in mind that the register in the video is wall mounted while the
registers in you home may be on the ceiling.
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