The ATTMA Trade Association has developed a Blower Door Fan Capacity Calculator to help ATTMA members calculate how many fans are required for Level 2 buildings.

The fan capacity calculator works on the basis of some assumptions such as a quality power supply and running into a free air unobstructed route.  The fans that can be used are: Infiltec, Retrotec (1000, 2000, 3000, 5000 and 6000 series) and The Energy Conservatory (Model 3, Model 4 and Ductblasters).

The tool requires the blower door fan, the target air permeability and the size of the building (surface area) to be identified. The calculator will provide you a reasonable estimate for the number of fans that will be needed.

Please note, as per the ATTMA guidance, you should always take approximately 20% more fan power than required to allow for a higher result. It is not uncommon for the target to be changed post test. Taking an extra 20% fan power will allow the result to still be valid and used for compliance.

Tests must always meet 50Pa Induced Pressure to be valid.