Should trickle vents be left open in winter?
What a trickle vent is sized to do, why closing it in cold weather is the wrong instinct, and the small number of times it is reasonable to shut one.
- Difficulty
- beginner
- Time
- 10 min
- Read
- 3 min
Short answer
Yes. They are designed to be open, and the winter is exactly when they earn their keep, because that is when windows stay shut and moisture builds up. The heat lost through them is small; the mould caused by closing them is not. Shut them briefly in a gale or if a room is genuinely unusable, and open them again.
Trickle vents are the small closable slots in the head of a window frame, and they are the purpose-provided background ventilation for the room. They exist because a modern sealed window otherwise gives a room no air change at all, and they are sized to give a small continuous flow rather than a draught. Almost everyone closes them at the first cold snap.
Step by step
- Find them all.One in the head of most openable windows, sometimes in the frame, sometimes as a slot through the glazing unit itself. Look along the top of each frame inside and check the position of the flap.
- Open every one.The lever or slider is usually on the inside face. Open means the flap is clear of the slot; some designs are counter-intuitive, so look for the airflow rather than trusting the label.
- Clean them.The external grille clogs with dust, cobwebs, paint and in some cases has been painted shut. A vacuum and a small brush restores the airflow, and a painted-over external grille needs carefully freeing.
- Leave them open through the heating season.That is the period they are for. A house with the windows shut for five months and no background ventilation is where condensation problems come from.
- Keep the internal doors of wet rooms shut and their fans running.Trickle ventilation moves the background air; extract fans remove the burst of moisture at source. They do different jobs and you need both.
- Judge the heat cost honestly.The total open area of a house's trickle vents is small — far smaller than the gaps a draughty old window had. The energy cost is minor against the cost of repairing mould damage and running a house at higher humidity.
- Close one only for a specific reason.A storm driving rain into the vent, unusual noise from a specific window, or a room being temporarily unusable. Then reopen it.
Tips
- If a room feels draughty at the vent, the issue is usually the position of a chair or a bed rather than the vent itself. The airflow is small and it warms quickly.
- If your house has no trickle vents at all and you have condensation, retrofitting them is a small job and is often the cheapest ventilation improvement available.
- Some newer vents are humidity-sensitive and open further as humidity rises. If you have those, leave them alone and let them work.
Common mistakes
- Closing every vent in October and reopening them in spring — That is precisely inverted. The winter is when the house is sealed, the moisture load is highest and the surfaces are coldest, so it is the season the ventilation is needed most.
- Painting over the external grilles when decorating — It blocks the vent completely while leaving the internal lever apparently working, so the room has no ventilation and nobody knows.
Questions people ask
How much heat do they lose?
Not much. The open area is small and controlled, which is the whole point of a purpose-provided vent as opposed to random gaps. The heat lost is a fraction of what an old draughty window lost, and the moisture benefit is large.
Do I need them if I have an extract fan?
Yes. An extract fan removes air, and that air has to be replaced from somewhere. Without vents, the fan is fighting a sealed box and moves far less air than it is rated for.
What if my windows have none?
Then the house is relying on leakage or on nothing. Retrofit vents can be fitted through the frame or over the frame on most windows, and it is a small job compared with dealing with the mould that follows.