Air Changes Calculator — Required ACH Per Room Type

This calculator determines the required ventilation rate for any room type by looking up a typical design air-change-per-hour (ACH) value, then multiplying by the room volume. For UK dwellings the legal minimum is set by Approved Document F as a litres-per-second extract rate — use the Domestic Kitchen option for that figure.

Calculation formula

Total air volume (m3/h) = Room volume (m3) x Air changes per hour (ACH)

Total air volume (l/s) = Total air volume (m3/h) / 3.6

Data sources

The ACH ranges in the lookup are conventional engineering design values drawn from general industry and CIBSE design guidance. They are rules of thumb for sizing, not statutory figures, and published industry sources differ by a few ACH for the same room type — always confirm against your project design brief and the relevant CIBSE/HTM guidance. (Standards such as CIBSE Guide A and ASHRAE 62.1 express ventilation as a litres-per-second rate per person and per unit floor area rather than as a room-type air-change figure, so no single published table is the source of these ACH numbers.)

Important: UK Building Regulations Approved Document F (2021 edition) expresses dwelling ventilation as litres per second, not as air changes per hour. Table 1.1 (intermittent extract) sets the legal minima for dwellings: kitchen 30 l/s (ducted hood adjacent to the hob) or 60 l/s (no hood or a recirculating hood), utility 30 l/s, bathroom 15 l/s and WC 6 l/s. Table 1.2 (continuous extract) sets the high rate: kitchen 13 l/s, utility 8 l/s, bathroom 8 l/s and WC 6 l/s. Select the Domestic Kitchen option to use the Part F 30 l/s figure directly.

The calculator provides minimum, typical, and maximum ACH values for each room type. The typical value is used by default, but you can override it with a custom ACH rate in the advanced options.