Ventilation for Kitchens and Bathrooms

Kitchens and bathrooms produce moisture and pollutants far faster than living rooms or bedrooms, and they therefore need ventilation that is stronger, faster and more directly targeted than background ventilation alone. A shower can add a large amount of water vapour to a small bathroom in minutes, cooking adds vapour, grease, particles and, from a gas hob, nitrogen dioxide, and both rooms have surfaces, mirrors, tiles and cold corners, where that vapour condenses quickly if it is not extracted. Background trickle vents, which suit a bedroom, cannot keep up with a shower or a frying pan, so wet rooms need extract fans, or a mechanical system, that can boost to a high rate when the room is in use and then fall back to a low background rate afterwards.

Extract rate, ducting and control together decide whether that boost actually works. A fan rated for a high airflow on paper will deliver far less if its duct is long, narrow or convoluted, if its external terminal is blocked or if its control never triggers, so a wet room fan should be judged by installed airflow, not by catalogue airflow alone, and its control, whether humidistat, timer, light switch or continuous running, should match how the room is actually used.

A ducted hood captures cooking pollutants at source, above the hob, and removes them outside, which is more effective for grease and nitrogen dioxide than a wall fan elsewhere in the room, while a recirculating hood filters grease and some odours but returns air, and moisture, to the room, so it does not replace extract ventilation for humidity. Hood ducting should be short, smooth and properly terminated, with a grease filter that is cleaned regularly, since a clogged filter reduces airflow and increases fire risk.

Bathroom ventilation, by contrast, is mainly about moisture and timing. A humidistat fan that runs until humidity falls, or a timer fan that overruns after the light is switched off, handles a shower better than a fan that stops the moment the light goes out, leaving steam to condense on cold surfaces. A fan in a windowless bathroom, or in a bathroom with no opening window, is especially important, since there is no purge ventilation alternative on a damp day, and its duct must terminate outside, not in a loft, where moisture will condense and damage structure.

Check each wet room fan for airflow, noise, control behaviour and duct termination, and note how long steam takes to clear after a shower and how long cooking smells linger after cooking, since those times are practical measures of extract effectiveness. Check cooker hood filters, duct routes and terminals, and whether any fan or hood is switched off because of noise, which is a sign that a quieter fan or a better duct route is needed, not that ventilation is unnecessary.

Trickle vents, door undercuts or a mechanical supply route should be part of the wet room assessment, not an afterthought.

In the EU, kitchen and bathroom ventilation rates follow national building regulations, with member states differing on required extract rates, on whether humidistat control is required, on cooker hood ducting rules and on whether continuous mechanical extract is the baseline for wet rooms. A fan rate that meets the rules in one country may fall short in another, so the local rate for the property should be checked.

In the UK, Approved Document F sets extract rates and control expectations for kitchens and bathrooms in England, with devolved equivalents elsewhere, and electrical safety rules govern fan work in bathrooms, including zones and protection. Those documents, together with maker guidance for hoods and fans, set the baseline for a compliant wet room system.

A common mistake is fitting a fan with a short timer overrun, so it stops while steam is still in the air, leaving condensation to form on mirrors, tiles and cold corners. Another is ducting a bathroom fan into a loft, where moisture condenses on cold roof timbers and insulation, causing hidden damage that is blamed on a roof leak rather than on the fan duct.

A third mistake is relying on a recirculating cooker hood for moisture control, when it returns humid air to the kitchen and does nothing for steam from a kettle, a dishwasher or a boiling pan elsewhere in the room. Hood and extract fan are complementary, not interchangeable, and both should be assessed for a kitchen.

Keep the fan and hood specifications, the installed airflow notes where measured, the duct layout and termination details, the control settings and the filter cleaning schedule. Those papers let a later occupant or engineer restore wet room ventilation that has been switched off or blocked, rather than replacing it unnecessarily.

Ask a qualified installer: what extract rate is proposed for each wet room, how is it controlled, where do ducts terminate, what cooker hood type is proposed and why, and how should filters and fans be maintained. Wet-room-specific answers show a system designed for moisture and cooking, not a generic fan.