Should I Keep My Trickle Vents Open?

Trickle vents are the little slotted vents in the top of most modern window frames. People close them because they feel a draught or think they’re losing heat, and then wonder why the windows are streaming and there’s mould in the corners. I’d say keep them open.

What they do

Old houses used to ventilate themselves through draughty sash windows, open fireplaces, gaps in floorboards and chimneys. When we fit airtight double glazing, block the fireplaces and seal everything up, all that accidental ventilation disappears, but we still produce just as much moisture. Trickle vents put back a small, controlled amount of background ventilation so the moist air has a way out.

Building regulations guidance in England expects replacement windows not to make a home’s ventilation worse, which is why most new windows come with trickle vents fitted. They’re there to do a job.

What about draughts and heat loss?

The amount of air coming through a trickle vent is small. In return you get drier air, which is easier and cheaper to heat than damp air, and fewer mould problems. If one is genuinely whistling or blowing in, check it’s fitted the right way and the cover is clipped on properly. On very windy, exposed elevations, some vents have adjustable or wind-resistant designs.

Getting the most from them

• Leave them open all the time, including overnight in bedrooms, which is when a lot of condensation happens.
• Clean them. The slots fill up with dust, dead flies and paint. A vacuum and an old toothbrush sort that out.
• Don’t paint over them or tape them up.
• Remember they’re background ventilation. Bathrooms and kitchens still need extractor fans.

If your windows don’t have trickle vents and you’ve got condensation problems, there are options, from retrofitting vents into the frames to wall vents or mechanical ventilation. The right answer depends on the house.

Trickle vents are one of the cheapest anti-mould measures there are. They’re already fitted and paid for, so use them.