What are Double Glazed Window Trickle Vents for?

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Adding trickle vents to a double glazed window.

Humble double glazed window trickle vents can be easily overlooked. However, they do have an important part to play, especially in rooms that can be subject to high humidity.

Kitchens and bathrooms are notorious for high humidity, both cooking and bathing use hot water that generates moisture in the air.

Trickle vents are going to be required for:

Your installer should be able to give you advice on your particular situation.

What is a trickle vent?

Trickle VentsThe purpose of the trickle vent in a double glazed window or door, is to allow for air circulation / ventilation without having to open the windows. They are designed to be effective for reducing condensation within a room and providing passive ventilation.

Did you know that even small family can produce about 26 pints of air moisture per day-  that’s over 3 gallons!

With properties becoming more & more insulated, the fitting of trickle vents to double glazed windows is promoted to avoid problems with condensation. As a result, you thereby avoid creating damp & mouldy patches within the home.

However, not everyone is a fan of the trickle vent, and they do have their advantages and disadvantages.


You can set them open or closed to your liking or when you feel you want to slowly circulate some fresh air into the room. They will have to be manually operated.

  • Trickle vents have proven ability to reduce condensation. Consequently, less condensation means less damp patches or unsightly black mould.
  • They can provide a flow of fresh air without having to open the window or door.


  • People think they are an unsightly addition that spoils the look of the frames.
  • Vents can be sometimes difficult to clean.
  • People complain that some Double Glazed Window Trickle Vents let in a lot of noise.
  • People complain about them “whistling” in windy conditions.

In Summary

Broadly, for replacement double glazed windows, if the old unit being replaced doesn’t have trickle vents, then the new one does not have to have them either. New- build houses (extensions) windows will require them.

The public (and industry) view on these types of vents is mixed. However, there are a lot of “haters” out there.

You may think, like many folks do, “why make a super energy efficient window then put a hole in it? When you can just as easily open the window or set it on a night latch”.

For rooms likely to suffer from high humidity (bathroom, toilet, shower, kitchen) they are better fitted than not.

There is a downloadable leaflet from the Glass & Glazing Federation (PDF) that gives some guidance. You can find it here: https://www.ggf.org.uk/publications/consumer-leaflets/guide-trickle-ventilators/

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