Blower door testing with crawlspace

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.

I’m not that person you seek, but I do have a question for clarification… (for my personal knowledge/education)…
Am I correct that you are stating the home DOES NOT have a “conditioned CS”, but DOES HAVE a breach in the CS envelope creating a significant leak between the CS and the home?

Good question: Conditioned crawlspace, typical of what we both see with well built homes in MN. Shallow soil with sloping building site is why a crawlspace was used. Electric boiler main level, boiler in utility closet on main floor. Baseboard in crawlspace.

1 Like

Thanks. That is what I thought you were describing, but you never stated that exactly, just kept referring to ‘leakage’ and ‘communication’.

1 Like