An airtightness test measures how well sealed a building's envelope is. It's used to determine how much heat is lost through ventilation and uncontrolled air leakage.
It's a key parameter the calculator uses when estimating ventilation losses, which in turn influences the overall heat load and the heat pump sizing. The better the documented airtightness, the more accurate (and often lower) the assumed losses can be.
You can choose from the following values:
No
Select this if nothing is known about the building's airtightness. The calculator will fall back to a conservative default assumption.
Yes
An airtightness test has been carried out. According to the DIN standard, a better value may be applied in this case.
Yes, volume flow known
The volume flow is known and specified in m³/m²/h. This represents the air change per square metre over one hour.
Yes, N50 value known
The N50 value is known — the air change rate measured at 50 Pa differential pressure (in 1/h), typically determined by a blower door test. It describes the volume of air that can escape through leaks in the building envelope.