What extraction rate does a cooker hood need in the UK?

Approved Document F specifies minimum extraction rates of 60 l/s (216 m³/h) for ducted cooker hoods and 30 l/s (108 m³/h) for recirculating hoods in domestic kitchens. If using a general extract fan instead of a cooker hood, the minimum is 13 l/s. Most quality ducted cooker hoods operate at 400-700 m³/h on their maximum setting, which exceeds the minimum requirement.

Do gas hobs need more extraction than electric?

Yes. Gas hobs produce combustion by-products including CO2, water vapour, and small amounts of NOx in addition to cooking fumes. This typically requires 20% more extraction than electric or induction hobs. More critically, gas hobs need adequate make-up air to prevent negative pressure, which could cause incomplete combustion. Gas Safe regulations require that replacement air can enter the kitchen at the same rate as the extract.

Is a ducted or recirculating cooker hood better?

Ducted hoods are significantly more effective as they remove moisture, grease, and odours from the building entirely. Recirculating hoods filter grease and some odours but return the moisture and heat to the kitchen. For gas hobs, ducted extraction is strongly recommended to remove combustion products. The Building Regulations set a lower minimum rate for recirculating hoods (30 l/s vs 60 l/s) because they do not contribute to the whole-house ventilation strategy.

What size duct do I need for a cooker hood?

Most domestic cooker hoods use 150mm (6-inch) diameter rigid duct for optimal performance. Some compact hoods use 125mm or 100mm duct, but this increases back-pressure and noise. Never reduce the duct diameter below the hood outlet size. Use rigid metal or semi-rigid aluminium duct rather than flexible duct wherever possible — flexible duct has 3x the friction loss and should be kept under 1m in length.

What is make-up air and why does it matter?

Make-up air is the replacement air that enters the kitchen to balance the air being extracted. In modern airtight homes, a powerful cooker hood can create significant negative pressure, which makes doors hard to open, causes draughts through gaps, and — most critically for gas hobs — can affect the combustion of gas appliances. Make-up air is provided through trickle vents, background ventilators, or dedicated air inlets. For gas installations, Gas Safe requires adequate make-up air.

Cooker Hood Extraction Calculator — Kitchen Ventilation

Calculate the required extraction rate for cooker hoods based on hob type, kitchen layout, and hood type. UK Building Regulations and Gas Safe compliant.

Kitchen Length

Kitchen Width

Hob Type

Gas hobs require more extraction due to combustion

Kitchen Layout

Open-plan needs higher extraction to prevent odour spread

Hood Type

Ducted removes air; recirculating filters and returns

Ceiling Height

How We Calculate This

This calculator determines the required cooker hood extraction rate based on Approved Document F minimum rates, adjusted for hob type, kitchen layout, and hood type. It also calculates the duct size and make-up air requirements.

Base extraction rates

Ducted cooker hood: 60 l/s (216 m\u00B3/h) minimum per ADF
Recirculating cooker hood: 30 l/s (108 m\u00B3/h) minimum per ADF
General kitchen extract: 13 l/s minimum (no hood)

Adjustment factors

The base rate is adjusted for hob type (gas +20%, induction -10%) and kitchen layout (open-plan +30-50%). Gas hobs generate combustion by-products that require higher extraction and dedicated make-up air per Gas Safe regulations.

Duct sizing

The duct diameter is calculated for a target velocity of 4 m/s and rounded to the next standard size. Pressure drop is estimated from duct material, length, bends, grille resistance, and filter loss (for recirculating hoods).