Home ventilation explained
Ventilation is how moisture leaves your home. Older houses ventilated themselves through gaps and chimneys; modern, draught-proofed homes need it designed in. Here's how each option works and where it fits.
The principle: remove moisture where it's made
Good ventilation has two parts:
- Extract from the rooms that produce the most moisture — kitchens, bathrooms and utility rooms — as it's produced.
- Background ventilation everywhere else: a small, steady exchange of air that carries away moisture from breathing and everyday living.
Cold outdoor air holds little water even on a damp day, so swapping it for indoor air almost always dries the home. The cost is some lost heat — usually much less than people expect. Our open-window calculator shows the trade-off.
Options compared
| Option | How it works | Best for | Watch out for |
|---|---|---|---|
| Trickle vents | Small slots in window frames for constant background airflow | Every habitable room | Often closed or painted over; need cleaning |
| Intermittent extractor fans | Switched on during showers or cooking | Bathrooms, kitchens, utility rooms | Too short a run time; poor ducting; weak airflow |
| Continuous fans (dMEV) | Quiet fans running all the time at low speed, boosting when humid | Bathrooms and kitchens with persistent mould | Need trickle vents or gaps under doors to draw air |
| Positive input ventilation (PIV) | A unit (often in the loft) gently pushes filtered air into the house, displacing moist air out through gaps and vents | Houses with whole-home condensation, especially with a loft | Can feel cool in winter without a heater; less effective in very airtight homes |
| MVHR (heat recovery) | Extracts from wet rooms, supplies fresh air to living rooms, and transfers heat between the two airstreams | Airtight new builds and deep retrofits | Needs ducting throughout; filters must be changed; costly to retrofit |
| Opening windows | Simple, effective air exchange | Short bursts after showers, cooking or waking | Security, noise, heat loss if left open for hours |
Getting more from what you already have
- Open every trickle vent and leave them open. Vacuum them if they're clogged.
- Test your fans with the tissue test (see bathroom condensation) and fit overrun timers so they run 15–20 minutes after use.
- Leave about a 1 cm gap under internal doors so fans and PIV can move air around the house.
- Use a cooker hood that vents outside. Recirculating hoods filter grease but return the moisture to the kitchen.
- Don't block air bricks or vents to stop draughts; they often ventilate floor voids or appliances.
How much ventilation is enough?
Building regulations in each UK nation set minimum ventilation for new work. In England this is Approved Document F, which specifies extract rates for kitchens and bathrooms and background ventilation for habitable rooms. Wales, Scotland and Northern Ireland publish their own equivalents. For an existing home, the practical test is simpler: if winter humidity stays above about 65–70% and surfaces get wet, ventilation (or moisture production) needs attention. See ideal humidity.
Ventilation vs dehumidifiers
A dehumidifier removes moisture without exchanging air, which helps when ventilation is difficult — a ground-floor flat with security worries, or a single damp room. It costs electricity and treats one room at a time. Ventilation treats the whole home and also removes other indoor pollutants. Many homes do best with both. Compare costs with our dehumidifier calculator, or let the full assessment compare ventilation, heating and a dehumidifier for your room.
Renters: broken extractor fans, missing trickle vents and windows that can't be opened are usually landlord repairs. See renters' rights.