What are the four ventilation systems in Part F?

System 1: Background ventilation (trickle vents) + intermittent extract fans in wet rooms. System 2: Passive stack ventilation (natural draught ducts). System 3: Continuous mechanical extract ventilation (MEV). System 4: Continuous supply and extract with heat recovery (MVHR). Any system can be used for any dwelling.

How do I calculate the whole building ventilation rate?

The whole building rate is the greater of: 0.3 l/s per m2 of floor area, or the number of occupants x 8 l/s (with a minimum based on number of bedrooms + 1). For a 100m2 3-bed house, this would be max(30 l/s, 32 l/s) = 32 l/s.

What extract rate does a kitchen need?

A kitchen needs 30 l/s intermittent extract (when cooking) or 13 l/s continuous extract. This can be provided by an extract fan, ducted cooker hood, or connection to a centralised MEV/MVHR system. Recirculating cooker hoods do not satisfy Part F.

What is MVHR and when should I use it?

MVHR (Mechanical Ventilation with Heat Recovery) supplies fresh air and extracts stale air through a heat exchanger recovering up to 90% of heat. Best for airtight buildings (air permeability below 3 m3/hr/m2). Costs £2,500-£5,000 installed but saves £100-£200/year on heating.

Do I still need trickle vents with MVHR?

With MVHR (System 4), trickle vents are not required for background ventilation as the MVHR provides continuous supply air. However, openable windows are still needed for purge ventilation (1/20th of floor area). With Systems 1, 2 and 3, trickle vents are mandatory.

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Part F Ventilation Calculator — Extract Rates & Trickle Vents

Calculate Part F ventilation requirements: extract rates by room type, whole building ventilation rate, trickle vent sizes and system selection (MEV/dMEV/MVHR).

Total floor area

Bedrooms

Bathrooms

En-suites

Ventilation system

How We Calculate This

This calculator determines ventilation requirements per Approved Document F for UK dwellings.

Extract rates

Kitchen: 30 l/s intermittent or 13 l/s continuous. Bathroom/en-suite: 15 l/s or 8 l/s. Utility: 15 l/s or 8 l/s. WC: 6 l/s.

Whole building rate

The greater of 0.3 l/s per m2 floor area or 8 l/s per occupant.

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.