Free Tool

Building Pressure Balance with Fan Flow Curve Spreadsheet

The air tightness of a small Passive House can present issues for exhaust ventilation strategies that rely on the building enclose to leak make up air.

In this spreadsheet, an example of a 400 CFM exhaust fan is used to illustrate this issue.


The fan manufacturer’s fan flow curve is used to generate an equation representing the amount of airflow the fan will produce working against different pressures. Using the blower door test leakage for the building enclosure, another equation is generated to represent the building enclosure leakage airflows, for different building pressures.


These equations are used to calculate the expected amount of air the fan will actually exhaust from the building with no other provision for make-up air. This is done by adjusting the airflow used by these two equations, until the two equations produce the same pressure.


This would be the amount of air the fan will exhaust from the building with no other provision for make up air.


With this spreadsheet you can change the building volume, and adjust the Exhaust flow rate in CFM, until the Building Depressurization equals the Fan working pressure. This is the airflow the fan would move without any additional make up air for the new building volume.

About the Author

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Mike Duclos
Principal, DEAP Energy Group, LLC

Mike Duclos is a principal and founder of The DEAP Energy Group, LLC, a consultancy providing a wide variety of Deep Energy Retrofit, Zero Net Energy and Passive House related consulting services. Mike was an energy consultant on the Transformations, Inc. Zero Energy Challenge entry, and has worked on a variety of Zero Net Energy, DER and Passive House projects,...[more]

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This tool is used in HeatSpring's Passive House in the Real World course.

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