Ventilation
Whole dwelling ventilation rate (Approved Document F)
- where
- bedroom-based rate (l/s)
- number of bedrooms
- floor-area rate (l/s)
- total internal floor area (m²)
- whole dwelling ventilation rate (l/s)
- whole dwelling ventilation rate (m³/h)
Explain this equation
Works out the minimum whole dwelling ventilation rate from Approved Document F, for sizing continuous extract or MVHR.
Two rules are applied and the larger wins. One is based on bedrooms, because occupancy drives moisture and pollutants: 19 l/s for one bedroom and 6 l/s more for each extra bedroom (13 l/s for a studio). The other is 0.3 litres per second for each square metre of floor. Multiplying litres per second by 3.6 gives cubic metres per hour.
A lookup-based minimum, taking whichever rule demands more air.
Sense check: a 3-bed, 90 m² home needs the bedroom rate of 31 l/s (the floor-area rate is only 27), about 112 m³/h.
Watch out: this is the continuous whole-house rate. Kitchens and bathrooms also need their own extract rates.
Finds the minimum continuous whole dwelling ventilation rate: the greater of 0.3 l/s per m² of floor area and the bedroom-based rate in Approved Document F Table 1.3.
Enter your values to see the result.
Good to know
Table 1.3: 1 bedroom 19 l/s, 2 bedrooms 25, 3 bedrooms 31, 4 bedrooms 37, 5 bedrooms 43, plus 6 l/s for each extra bedroom; 13 l/s where the dwelling has only one habitable room. The rate is what a continuous extract or MVHR system must deliver in normal running. The 2026 edition (in force 24 March 2027) keeps the same figures.
Common mistake
Using only the bedroom table for a large dwelling. In bigger homes the 0.3 l/s per m² rule usually governs.
Limits
England. Wales and Scotland have their own guidance. Intermittent and boost extract rates are separate (Table 1.1 and 1.2).
Sources
- HM Government, Approved Document F Volume 1: Dwellings, 2021 edition (para 1.24 and Table 1.3 whole dwelling ventilation rates; Table 1.7 background ventilators; para 1.64 continuous extract; paras 1.45–1.46 airtightness; Section 3 existing dwellings)
- HM Government, Approved Document F Volume 1: Dwellings, 2026 edition (in force 24 March 2027; Table 1.3 and Table 1.7 values unchanged)
Results are calculations from the published methods and figures shown, and depend on the data you enter. Follow BS EN ISO 6946, BS 5250, PAS 2035, Building Regulations Part L and manufacturers’ data. Whole-house retrofit needs a qualified retrofit assessor and coordinator.