Ventilation at Home: How to Get It Right in the UK
A plain-English guide to home ventilation in the UK: trickle vents, extractor fans, air bricks, when to open windows and how to avoid wasting heat.
A well-insulated, draught-free home is cheaper to heat but traps moisture and pollutants unless air has somewhere to go. That balance is the reason ventilation matters. Too little, and you get condensation, mould and stale air. Too much, and you waste heating. The target is controlled ventilation: moving air where and when it is needed.
The three kinds of ventilation
- Background ventilation: Small, constant openings such as trickle vents in window frames and air bricks in walls. Keep them open.
- Extract ventilation: Fans in kitchens, bathrooms and utility rooms that remove moist air at source.
- Purge ventilation: Opening windows wide for a short time to flush out air quickly, such as after cooking or showering.
Each plays a part. Relying on only one rarely works.
Where ventilation matters most
Bathrooms
Showers produce large amounts of moisture in minutes. Run the fan during the shower and for about 15 to 20 minutes afterwards. If the fan seems weak, hold a tissue against it; it should be sucked on to the grille. If not, clean it, check the duct, or ask an electrician about replacement.
Kitchens
Use the cooker hood or an extractor fan, and ideally vent it outside. A recirculating hood filters grease but returns moisture to the room. Lids on pans reduce steam.
Bedrooms
A person exhales moisture overnight, especially with doors closed. Keep trickle vents open and consider cracking a window, particularly in rooms with mould problems.
Utility rooms and drying areas
Tumble dryers need venting outside or a condensing model that collects water. Drying laundry indoors is a leading cause of winter condensation.
Trickle vents: use them
Small slots on top of window frames are often left closed because people feel draughts. They let in a small, steady flow of fresh air. If yours are painted over or broken, they are cheap to fix. If a window has no trickle vent, a window fitter can sometimes add one.
Air bricks and permanent vents
Air bricks keep suspended timber floors dry and supply air to some heating appliances. Do not block them with soil, garden beds or insulation. Gas fires, wood burners and some boilers need an air supply, and blocking it can create carbon monoxide risks. Have fuel-burning appliances checked by an appropriately qualified person, and see our carbon monoxide alarm guide.
Smart ways to ventilate without losing heat
- Open windows for short bursts of 5 to 10 minutes, with internal doors closed, rather than leaving one slightly open all day.
- Ventilate at warmest part of the day when outside air carries less moisture than your cold evening air.
- Use humidity-sensing extractor fans that run only when needed.
- Heat rooms evenly. A cold bedroom with a warm hallway can lead to condensation as warm, moist air from other rooms drifts in.
Mechanical ventilation and heat recovery
Very airtight modern homes, and some renovations, use mechanical ventilation with heat recovery (MVHR), which supplies fresh air while retaining much of the heat. These systems need maintenance such as filter changes. If you have one, keep the manual and replace filters according to instructions.
If you are retrofitting a house with new insulation or windows, ask your installer about ventilation as part of the design. Draught-proofing in an already damp home without adding ventilation tends to make things worse. See draught-proofing basics for the balance.
Signs you need more ventilation
- Persistent condensation on windows
- Mould on ceilings or in corners
- A musty smell in bedrooms or wardrobes
- Peeling paint or wallpaper in bathrooms
- Headaches or stuffiness in a closed room
Our condensation guide covers what to do first.
If you want an extractor fan fitted or a ventilation system assessed, you can search on Compito, compare ID-verified local providers and send a request. Electrical work must be done by a competent registered electrician.
A worked example: a mid-terrace with a damp bathroom
A bathroom has a window and a weak fan. Mould appears on the ceiling every winter. The household changes three things: the fan is replaced with a quieter, more powerful model that runs on a timer after the light is switched off, the door is kept closed during showers and a window is opened for ten minutes afterwards. The ceiling is cleaned and repainted with a suitable paint. The mould does not return. The decorating was less important than the ventilation.
How much ventilation is enough?
There is no single number that suits every home. Factors include the number of people, how much cooking and washing happens, how airtight the home is and the heating pattern. Building regulations set minimum standards for new work. In an existing home, use symptoms as your guide: if windows run with water daily or mould appears, you need more extraction or more control of moisture.
Fans: choosing and maintaining
- Choose a fan sized for the room and with a run-on timer or humidity sensor.
- Check the duct goes outside, not into the loft, and that it slopes so condensation drains away from the fan.
- Clean the grille and blades from time to time.
- Electrical work and fans in bathroom zones should be done by a registered electrician.
Homes with fuel-burning appliances
Open-flued boilers, gas fires and wood burners rely on a permanent air supply. If you add an extractor fan in the same room, ask a qualified engineer whether it could draw fumes back down the flue. Never block the vent for a fire or boiler, and keep a carbon monoxide alarm working.
Renting and flats
Tenants can use extractor fans and open windows but should ask before changing fixed ventilation. In flats, shared ducts and fans may be managed by the building. Report faulty fans and vents in writing; see mould in a rented home.
Air quality beyond moisture
Cooking fumes, cleaning products, candles and wood smoke all affect indoor air. Ventilating while cooking, using lids and fans, and reducing sprays and fragrance can help. People with asthma or allergies may benefit from more regular airing and from keeping damp under control.
Frequently asked questions
Should I keep trickle vents open in winter?
Yes. They provide a small, steady airflow that helps stop moisture building up, and the heat loss is modest.
Can I just leave a window open instead of using a fan?
A window helps, but fans remove moist air at the source and work when you are not home. Use both where practical.
Do I need a ventilation system after fitting new windows?
New airtight windows can increase condensation if no background ventilation is provided. Check they include trickle vents and keep them open.