Room Ventilation Calculator

A trickle vent is a small opening built into a window frame that provides background ventilation. Under Part F 2021 (Approved Document F Volume 1), they are required in all new and replacement windows to ensure adequate air quality. The minimum equivalent area (EA) per ADF 2021 Table 1.7 is a per-room figure (which may be split across several ventilators): 8,000 mm² for habitable rooms and kitchens in a multi-storey dwelling, rising to 10,000 mm² in a single-storey dwelling; 4,000 mm² for bathrooms (the same in both cases). WCs and utility rooms have no minimum background ventilator requirement in Table 1.7. Para 1.57 also requires at least 5 background ventilators across the habitable rooms and kitchens of a dwelling (at least 4 in a one-bedroom dwelling).

Under Part F 2021 (ADF 2021 Table 1.1), a kitchen requires an intermittent extract rate of 30 l/s if the extract is a cooker hood directly over the hob, or 60 l/s if positioned elsewhere in the room. Continuous extract is 13 l/s (Table 1.2). Intermittent fans are typically controlled by a switch or humidistat. The extract point should be positioned as close to the hob/cooker as possible for maximum effectiveness.

Purge ventilation is rapid ventilation to dilute pollutants (e.g., after painting or a smoke event). Part F (ADF 2021 para 1.27) requires the ability to achieve at least 4 air changes per hour (ACH) via openable windows or external doors. The minimum openable area depends on the window type (ADF 2021 Table 1.4): 1/20th of the floor area for hinged or pivot windows that open 30° or more, sash windows and external doors; 1/10th of the floor area for hinged or pivot windows opening between 15° and 30°; windows opening less than 15° are not suitable for purge ventilation. For a 4m × 3m (12 m²) room with a window opening 30° or more, that's 0.6 m² of openable area; for a 15–30° window it would be 1.2 m².

A bathroom requires an intermittent extract rate of 15 l/s or a continuous rate of 8 l/s under Part F. The fan should be connected to the light switch with a 15-minute overrun timer. In bathrooms without windows (internal), mechanical extract is mandatory. Fans must be ducted to outside, not into the loft.

Yes. A WC requires intermittent extract of 6 l/s or continuous at 6 l/s (ADF 2021 Tables 1.1/1.2). A WC has no minimum background ventilator (trickle vent) requirement under ADF 2021 Table 1.7, but a trickle vent is still good practice where a window is fitted. Internal WCs without windows must have mechanical extract. The extract should have an overrun of at least 15 minutes to clear the air after use.