A couple of weeks ago we had our first blower door
test. A blower door test tests air
leakage in a building. This test, the
first of several we expect, was meant to see how tight the frame of the house
is.
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| The builder next to the blower door |
Since the windows and doors haven’t been installed, window
and door openings were all sealed, either with house siding (i.e. they haven’t
been cut out yet) or taped shut with plastic.
A special blower was placed in the front door. First, the blower pulled air out from the
house, depressurizing it to 50 pascals.
Air pressure inside the house was less than air pressure outside causing
air outside to be sucked into the house.
A meter then measured how much air entered the building.
The passive house standard requires that air leakage in a
building be limited to 0.6 ACH (air
change per hour) at 50 pascals. This
means that when the house is pressurized to 50 pascals pressure differential
between inside and outside, 0.6 of the volume in the house will leak in or
out each hour. For a house the size of ours we were
looking for a reading of 350 (not sure what units) from the meter to meet the Passive House standard. The meter
reading was 220 or less than 2/3 of the Passive House threshold.
For comparison, our builder told us he performed the blower
door test on his own home, a typical leaky home, and got a meter reading of
4000. At another client’s home where
they took a leaky home and did some energy efficiency work, the meter reading
after the energy efficiency work was 1900.
This illustrates that it’s much easier to build a house that’s air tight
than it is to take a leaky house and make it air tight.
Air leakage is measured when a building is pressurized
because it’s much more difficult to measure under normal conditions. The pressurized readings can then be
mathematically converted to normal condition readings (by dividing by 16 or 17). The Passive House standard of 0.6 ACH at 50
pascals converts to about 0.035 ACH without a pressure differential. This means that under normal conditions only
3.5% of the air volume in a house will leak out per hour. Compare this to our builder’s leaky home
where more than 50% of the volume of air will leak every hour. Much of the energy that a building loses is
through air leakage. We can see here that our house will lose a
small fraction of the energy that a typical leaky house loses. This is a clear example of how putting a
little thought and energy into the early stages of construction can make a home
much more energy efficient without a big expense.
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| Fogging the seams inside the building |
After the air leakage readings were taken, the builder broke
out a fog machine. This time, the blower
door fan was reversed to pull air into the building and create higher pressure
inside. Fog was blown against all the
seams inside the building while the framing crew looked for escaping fog outside
the building. The few areas where leakage
was found were marked and sealed with silicon or tape.
Here's a quick video showing the fogging from outside the building:
The next blower door test will probably take place after the
windows and doors have been installed.
