Download Energy Audits - Weatherization Assistance Program Technical

Energy Audits
The Ducts/Infiltration form - Pre/Post Whole House Blower Door duct measurements
5. Blower Door Subtraction
This method uses the same readings as the Whole House Blower Door
technique but adds analogous readings, both before and after duct sealing, during
which the distribution system has been sealed off from the rest of the house. Use
cardboard, plastic, tape, etc., to temporarily cover and seal all registers and grills
on both the supply and return side. This essentially allows subtraction of the house
leakage from the duct plus house leakage to isolate the leakiness of the ducts. One
additional reading is required to help compensate for duct leakage to the
conditioned space, the duct - house pressure differential with the ducts and
registers sealed and the house pressurized (or depressurized) to the same degree as
for the other CFM readings (normally 50 Pa).
Note, it is normally recommended that this technique not be used if the
measured duct - house pressure differential is less than 20 Pa, indicating that the
duct system is very well connected to the house interior. This is commonly true
in homes which use building cavities for a significant part of the duct work.
The data entry items for this input mode are as follows:
10/06 Draft
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