Air infiltration is typically THE MOST SENSITIVE assumption in all of Manual J. Small changes in air infiltration assumptions have a large impact on:
Sensible heating
Sensible cooling
Latent cooling
We offer two primary methods for calculating infiltration loads
The ACCA Manual J "tightness" method
Blower Door
The ACCA Manual J "tightness" method
This is the default method (Method: Tightness) for a project. You can select your assumption about the Envelope Tightness based on your observations in the room.
Set your "Tightness" assumption
For each option, we display guidance text to help you make more informed decisions:
Tight:
Would measure less than 2 ACH50 via blower door test
Only seen in high-performance homes
Semi-Tight:
~3 ACH50 via blower door test
Common for homes built since 2010 or homes with recent professional air-sealing improvements
Average:
~5 ACH50 via blower door test
Common for homes built 1980 - 2010s or pre-1950s home that has had recent professional air sealing improvements
Semi-Loose:
~7 ACH50 via blower door test
Common for homes built 1950 - 80s
Loose:
Greater than 10 ACH50 via blower door test
Common for homes built pre-1950
After scanning edit the "Living Area" to match the scanning area
The tightness calculations are also very sensitive to the Living Area you have entered. This value is often populated from the address lookup feature. Just below it you will see the Scanned Living Area - this is the calculated conditioned floor area of the home based on your scans.
After you have scanned all heated and cooled rooms in the home, you should edit the Living Area to match the Scanned Living Area.
Blower Door Method
Using real data is always preferred and more accurate than guessing how tight a home is. If you have access to Blower Door test results us the the Blower Door method. We offer two data options:
Blower Door (ELA4)
Blower Door (CFM50)
Blower Door (ELA4)
Enter the Effectitve Leakage Area.
NOTE: Do NOT guess at this value, only use numbers from a properly calibrated blower door test result.
Effective leakage area @ 4pa (ELA4) is the size (sq in) of an engineered opening that would produce the same amount of leakage as the cracks and penetrations in the building envelope at natural pressure differential i.e. 4 pascals.
Select a Shielding Class
Blower Door (CFM50)
Enter the Leakage CFM50 value (leakage rate in cubic feet per minute @ 50 pascals
NOTE: Do NOT guess at this value, only use numbers from a properly calibrated blower door test result.
Select a Shielding Class
