Automatic greenhouse vent openers
A greenhouse heats up fast on a sunny day, even in April. If you are at work, nobody opens the roof vent. An automatic vent opener does it for you: a cylinder of wax expands as it warms up and pushes the window open, then closes it again as the air cools. It needs no electricity and fits most aluminium roof vents.
Bayliss XL Autovent
The best known opener in the UK, with thousands of reviews
£25 at Amazon · 4.4 stars (4,030)
Autovent with 7 kg opening force
Opens from about 17 to 25°C according to the listing, well rated
£23 at Amazon · 4.6 stars (1,716)
Bayliss Autovent twin pack
Two openers for a greenhouse with two roof vents
£51 at Amazon · 4.5 stars (244)
Heavy-duty vent opener, 15 kg
Twin spring opener for heavier glass vents
£24 at Amazon · 4.1 stars (763)
Prices and ratings from Amazon.co.uk when we checked. Affiliate links. We have not tested these ourselves.
What to look for
- Check the lifting force against the weight of your vent. Glass vents weigh more than polycarbonate ones.
- Most openers let you set the opening temperature with a screw on the cylinder.
- Fit one opener per roof vent. A greenhouse with one small vent often needs louvres or an open door on hot days as well.
- Take strong winds into account. A wide-open vent can catch a gust, so do not set the opener to open too early.