What ventilation rate does a four-bedroom house need?

Under Approved Document F a four-bedroom home needs the greater of 0.3 l/s per square metre of floor area and 37 l/s. For a 120 square metre home that is the greater of 36 and 37, so 37 litres per second.

Is the ventilation rate based on floor area or bedrooms?

Both. Approved Document F requires the greater of the two, so you work out the floor-area figure and the bedroom figure and use whichever is larger.

What changes to the rate in 2027?

From 24 March 2027 the Future Homes Standard replaces the two-method calculation with a flat 6 litres per second per bedroom for the whole-dwelling supply rate.

Calculator

Ventilation rate calculator

This calculator works out the whole-dwelling ventilation rate your home needs under Approved Document F, the ventilation part of the Building Regulations for England. Enter the number of bedrooms and the internal floor area, and it returns the required supply rate in litres per second, using the greater of the two methods the regulations set out.

By VentRight Editorial · Last updated 2026-07-08 · Impartial · Sourced

How is the whole-dwelling ventilation rate calculated?

Approved Document F sets the whole-dwelling rate as the greater of two figures: 0.3 litres per second for each square metre of internal floor area, and a bedroom-based figure of 19 l/s for one bedroom rising by 6 l/s per further bedroom. This calculator works out both and returns the larger, which is the rate your supply air must meet.

The calculation runs on the server, so the answer is fixed and repeatable rather than depending on your browser. It covers only the whole-dwelling supply rate. The separate extract rates for kitchens, bathrooms and other wet rooms are set out in our Part F ventilation rates guide.

Sources: GOV.UK

Does this calculator use the current rules or the Future Homes Standard?

It uses the current 2021 edition of Approved Document F, which applies to work in England until 24 March 2027. From that date the Future Homes Standard changes the method to a flat 6 litres per second per bedroom. If your project completes after the changeover, use the Future Homes figure instead. See our Future Homes Standard guide.

The two methods can give different answers, so it matters which one applies to your project. For a scheme completing close to the deadline, check with your building control body which edition governs, and design to the newer figure if in doubt.

Questions

What ventilation rate does a four-bedroom house need?: Under Approved Document F a four-bedroom home needs the greater of 0.3 l/s per square metre of floor area and 37 l/s. For a 120 square metre home that is the greater of 36 and 37, so 37 litres per second.
Is the ventilation rate based on floor area or bedrooms?: Both. Approved Document F requires the greater of the two, so you work out the floor-area figure and the bedroom figure and use whichever is larger.
What changes to the rate in 2027?: From 24 March 2027 the Future Homes Standard replaces the two-method calculation with a flat 6 litres per second per bedroom for the whole-dwelling supply rate.

Tool · v1

Part F whole-dwelling ventilation rate

The greater of 0.3 l/s per square metre of floor area and the bedroom-based figure from Approved Document F Table 1.3.

With the default inputs (Bedrooms = 3, Floor area = 90 m2) the Whole-dwelling ventilation rate is 31 l/s.

Result

Whole-dwelling ventilation rate: 31l/s

How this works

This calculator applies Approved Document F, the 2021 edition for England. The whole-dwelling ventilation rate is the greater of 0.3 litres per second per square metre of internal floor area and the bedroom figure from Table 1.3, which is 19 l/s for one bedroom plus 6 l/s for each further bedroom. It does not use the Future Homes Standard method that applies from 24 March 2027.

Each result is computed on the server from the inputs above using a versioned formula stored in the database. This version (v1) has passed its 7-day test window and is the currently-live version. Nothing is calculated in your browser.