Automatic greenhouse vents puzzle

[Brian]

Automatic roof vents seemed a great idea for my new greenhouse which was put up in November - but they have never opened themselves yet. I now find that the automatic vents I have can only be set to open above 15 degrees & I want them to open at cooler temperature, to improve airflow. If you have automatic greenhouse roof vents, at what temperature do your vents open themselves?

[Mike P]

I used to have this problem with the budget ones I had in my greenhouses. I adjusted them to open at the lowest temperature they could but in the end reverted to manual opening in the winter.

[Keith H]

I fitted a couple of Bayliss auto vents when I built my secondhand greenhouse last autumn, at the time spending more on two vents than the greenhouse cost me seemed a little odd but I have been very pleased with them. They are not set to open at their lowest setting but still open when there is a bit of sun on them, they open at about ten deg. C, slightly higher if it is cloudy. I am now thinking about getting automatic openers for the louvers on the side walls aswell.

[Peter]

I've never found a need to buy automatic vent openers. When temperatures get to a reasonable level in Spring I open the roof vents and leave them open until late Autumn. That also applies to the door.

[DaveW]

I have auto vents on both top lights and side louvers. The simple expanding wax types will never be that adjustable. I presume you would need something like electronic control for the sort of accuracy you want. The wax type are affected by two things, the temperature of the greenhouse and also direct sun on the cylinder. In short whatever heats the black cylinder up. If the cylinder gets direct sun it will open before those in the shade do, the latter relying on the greenhouse temperature to open them.

However they were a godsend when I was working since I could go out early in the morning when it was frosty knowing if it would be sunny during the day they would open, but if cold when I returned they would have already closed.

As Mike and Peter say if you want that accuracy of control either leave one vent on manual, either top or louver that you can operate yourself in the winter and leave open day and night in summer as we used to do in the past, since the wax type auto vents will also close in the evening in summer unless it is very hot. I am too close to the road to leave greenhouse doors open and unlocked in summer as Peter does.

This would suit the type of accuracy you want:-

http://web4deb.blogspot.co.uk/2008/08/vents-20.html

[Nick_G]

I've never found a need to buy automatic vent openers. When temperatures get to a reasonable level in Spring I open the roof vents and leave them open until late Autumn. That also applies to the door.

Me too. I screen the doors and vents with plastic mesh to keep out birds, cats, foxes and our dog.

[Peter Cupial-Jones]

Broadly agree with the comments made so far. I use the Bayliss XL openers on my 2 roof vents and even when screwed down as far as possible they will still crack the vents open a little on a winters day. The other airflow management technique during winter time is the manual 'leavingthedooropenonaniceday' method. Like the other guys I start leaving the door open all day from mid-April and by end of May its open 24 x 7 until mid-September.

[Keith H]

Me too. I screen the doors and vents with plastic mesh to keep out birds, cats, foxes and our dog.

And that is another project for me, I need to make an inner mesh panel to take the place of one of the sliding doors, allowing ventilation but keeping the foxes out, perhaps I should try to make it bird and squirrel proof too.

(Far too much wildlife in London, I don't think I ever saw a fox or squirrel when I lived in rural East Yorkshire. )

[Rene G]

I am preplexed by the problems with automatic window openers! I have had a Baylis automatic vent for well over twenty years on one of my small greenhouse and I can set it for whatever temperature I choose. Mine is set at about 12 degr. C and it always works. One thing I have learned quite early that unless the Wax container that drives the Gauge is protected it can be damaged by the heat of the sun and it leeks out. So I have wrapped a cardboard sleeve round it, tying it with wire and it works fine.
At least it works, otherwise the plants would be cooking in the sun if I'm out for a day in the summer!

[DaveW]

They also do advocate removing the cylinder in winter Rene since they can be damaged by cold, but I leave mine in place.