Not sure if anyone knows the answer to my question: According to ANSI standards, when testing for air leakage with a blower door, the Air Changes per Hour (ACH) and CFM50/SqFt of floor space are calculated without the crawl space included in the CuFt and SqFt input.
What about a crawlspace well sealed from the outside enviromnent that has quite a bit of communication between the main house and the crawlspace?
I tested a house with a crawlspace that has no exterior crawlspace vents and a decently sealed exterior door scuttle. There is no scuttle access from the main floor to the crawlspace. Ducting from the HRV, plus a downdraft range vent improperly terminated in the crawlspace created quite a bit of air communication between the crawlspace and the main level.
I tested the depressurization of the main floor relative to the crawlspace. The fan was depressurizing the main floor. I depressurized the main floor at -40pa with the fan, and the crawlspace measured around -22pa.
If I calculate the ACH using ANSI standards, namely CuFt of the main level of the house, ACH-50 = 9.0. If I add the crawlspace volume, ACH-50 = 6.0.
The leakage I identified by smoke and IR makes me believe ACH-50 of 6.0 is the accurate reading. There were leakage issues, but no “smoking gun” that points to ACH-50 of 9.0.
Anyone who does this work, how do you report on this? When do you decide to include the crawlspace in your ACH50 calculations and when do you simply go by ANSI standards? Does my -40pa/-22pa pressure difference qualify to include the crawlspace in my CuFt calculations?
I know this is deep in the weeds, but I’m looking for feedback from someone who has more experience with this decision.