What Is Blower Door Testing?
The blower door measures air-flow at 50 pascals house pressure (CFM50), producing a number that is used to compare the leakiness of homes. The blower door also creates pressure differences between rooms in the house and intermediate zones like attics and crawl spaces that can give clues about the location and size home’s air leaks.
Measuring house pressure differences:
Connecting the manometer’s hoses correctly is essential for pressure testing. A widely accepted method for recording correct hose connection helps avoid confusion. This method uses the phrase “with reference to”, abbreviated “WRT” to discriminate between the input zone and reference zone for a particular measurement. The outdoors is the most commonly used reference zone for pressure diagnostics and is considered to be 0 pascals.
For example, house WRT outdoors = –50 pascals means that the house (input) is 50 pascals negative compared to the outdoors (reference or zero-point). The pressure reading in the last example is called the house-to-outdoors pressure difference.
There are two common ways to measure intermediate-zone pressures during blower-door testing. The first is measuring house WRT zone, also called the house-to-zone pressure. The second is measuring zone WRT outdoors, also called the zone-to-outdoors pressure. These two pressures should add up to –50 pascals, which is the house-to-outdoors pressure during a standard –50-pascal blower-door depressurization test. Therefore, the house-to-zone pressure plus the zone-to-outdoors pressure equals the house-to-outdoors pressure.
Because these intermediate-zone pressures add up to –50 pascals, subtracting either one of these zone pressures from –50 pascals gives you the other one. For this reason, many technicians
measure only one pressure, feeling confident that they know the other. Some technicians consider zone-to-outdoors more reliable because the outdoors is the reference zone for the
blower-door test. Other technicians prefer house WRT zone because you only need one hose connected to the manometer.
It’s often wise to measure both pressures—especially in complicated homes with multiple air-leakage problems.
We work with an independent energy auditor to assure our customers a high-level of quality and an independent, unbiased partner.
See www.mainehousing.org for more information.