I am working on building a cold frame and have purchased a Univent automatic opener to vent the cold frame by lifting the lid/light. However the Univent opener is not supposed to subjected to freezing temperatures or it will break. That is surprising to me because it seems most people would want to use an automatic opener during times of the year that there are freezing temperatures.

Does anyone know whether a Univent opener can handle freezing temperatures?

What are some alternatives for automatically venting a cold frame during the Winter?

  • 2
    Looks like univent wants you to take the cylinder out when temperatures are too cold. The danger seems to be that the cylinders would try to open a stuck frame and burst. This should be preventable if you make sure your frame cannot get frozen shut.
    – wax eagle
    Dec 15, 2011 at 13:37
  • 1
    I think that the danger is that the mineral gel that expands and contracts and actuates the opener will freeze and ruin the cylinder. But I'm not sure because I can't find any documentation that explains why it needs to be removed during freezing temperatures.
    – spesh
    Dec 19, 2011 at 1:39

4 Answers 4


I wish I could point to a bimetallic contraption that would open the lid, but after a little searching I haven't been able to find anything -- perhaps because that solution isn't strong enough to lift a lid? Maybe someone else knows of something in this category that would do the job?

I'll suggest taking a different approach, unfortunately with added complexity. Instead of lifting the lid:

  • run electricity to the cold frame
  • add louvered vents to two walls
  • in one of the vents, add an exhaust fan that is connected to a thermostat
  • make sure the other vent is oriented so that the louvers open when the fan is blowing out

Fortunately a hot cold frame is associated with sunlight, so you may be able to use a solar panel instead of connecting the cold frame to the grid.

If you get a lot of snowfall in winter, you'll need to make sure that the louvers do not get obstructed by snow. You'll also need to check regularly (daily?) that the louvers do not get frozen shut.

Also, there's a danger here that if the cold frame is humid during the day and temperatures drop rapidly some evening, the louvers could get stuck open and the interior could drop below freezing. This probably wouldn't be a problem in the dead of winter when all you've got growing are greens (which will generally recover from such a freeze). But it would be a disaster if you get a cold night in mid-spring when you're hardening off peppers or other cold-sensitive plant.


I found this product which claims to work at low temperatures. It's claim to fame is that it uses wax instead the mineral gel. Having done some work around greenhouses and looking outside my house at the freezing rain I agree with bstpierre that you need a robust solution that will stand up to snow load.

Commercial greenhouses use the end wall to place a louver with fans that is temperature activated. The only gotcha is that you must also screen the louver to prevent insects from coming in (like thrips) in the summer.

  • Given that you proposed the solution most similar to the current one I think you deserve the bounty.
    – wax eagle
    Feb 2, 2012 at 14:24
  • Wax based thermal actuators are always the best for broad temperature ranges. In the trucking industry, they're used for the actuator in the engine coolant thermostat as well as the radiator shutter air control. So, you have one that will take 195 degrees and the other exposed to sub-zero. Wax expansion works against a rubber sleeve that pushes on a stainless steel pin. Sep 8, 2013 at 21:17

I have a univent and left it in the garage over the winter and had to replace the cylinder. Something happens to the gel when it freezes

  • There were two parts to the question: one about freezing temperatures, the other about workarounds for them. Do you have any input on the second part to make this answer complete? Thanks, and welcome to the site.
    – Niall C.
    Sep 10, 2013 at 14:26

I've had Unidentifiable on my cold frame. In the fall I do remove the cylinder. Never needed the frame to open during winter months. Never got too warm in the frame when there's snow on glass or temps are below freezing anyhow. 7 years and cylinder is still functioning

  • 1
    HI Tony, what is unidentifiable? Can you describe it?
    – kevinskio
    Jan 20, 2023 at 12:46

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