Do not choose a heat recovery unit solely because it says suitable for up to 150 m². Air volume relates to room use, occupancy and residents. The unit must also deliver that volume against the actual duct resistance, not just under free-air conditions.
Room volume is calculated by multiplying floor area by height. In the educational example, 100 m² × 2,7 m = 270 m³. Using an illustrative air change rate of 0,5 per hour gives 135 m³/h. This example explains the units, but 0,5 air changes per hour is not presented here as a mandatory standard for every home.
In a real design, supply and extract air, connections between rooms and operating modes are assessed separately. Occupancy-based and air-change estimates must not be added blindly if doing so counts the same need twice.
Filters, grilles, ducts and their pressure losses matter. Setting the correct airflow requires adjustment of the entire system, not just choosing a fan percentage on the controller. S18, S19
Before ordering: provide a floor plan with heights and the number of occupants. Ask which airflow and resistance the specific unit has been selected for.
Information sources
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- S18
- S19
Sources checked on 2026-09-29. If the manufacturer has changed the product or documentation, follow the latest technical information for the specific model.