Ventilation Calculator — How Much Fresh Air Does Your Home Need?

Ventilation requirements for residential buildings are determined by European standards EN 15665 and DIN 1946-6. These standards ensure that indoor air quality remains healthy while minimising energy loss.

The calculation considers three main factors:

• Volume-based method — The building volume (floor area × ceiling height) multiplied by the required air change rate (typically 0.5 air changes per hour for residential buildings). This ensures the entire air volume is replaced every 2 hours.
• Person-based method — Each occupant requires a minimum of 25–30 m³/h of fresh air. In bedrooms, the minimum is 15 m³/h per sleeping person. Whichever method yields the higher value is used.
• Room-function method — Different room types have specific airflow requirements: kitchens need high extract rates (60+ m³/h) due to moisture and odours, while bedrooms need lower but steady supply.

Our calculator combines all three methods to give you the most accurate result. The detailed mode uses the room-function method from DIN 1946-6, which is the most precise approach for residential design.

A balanced ventilation system has two airstreams:

• Supply air — Fresh, filtered outdoor air delivered to "dry" rooms: bedrooms, living rooms, offices. These are the rooms where people spend the most time.
• Extract air — Stale, moist air removed from "wet" rooms: kitchens, bathrooms, WCs, utility rooms. These are the rooms that generate moisture, odours, and pollutants.

The two airstreams must be balanced: total supply should roughly equal total extract. This is where the heat recovery unit sits — between the two streams, recovering up to 95% of the thermal energy from the outgoing air.

Not sure which system type suits your building? Read our guide to choosing heat recovery for your home.