Greenhouses are designed to capture solar energy. However in climates with a lot of sun and in summer when the outside temperatures are warm, all that solar energy can overheat a greenhouse. The easiest and most reliable way to avoid this is to install automatic vent openers.
Greenhouses need to be designed to not only capture solar energy but also adequately ventilate excess heat if temperatures get too hot.
You should always make sure you have adequate vents in the roof of your greenhouse as heat rises and you want that heat to escape. However you should not leave the vents open at nighttime as you will lose any heat gain and cool your greenhouse too much.
Automatic vent openers are a great addition to your greenhouse and will save you lots of time and protect the plants in your greenhouse.
- Don’t need a long pole to open the vents
- Don’t need a manual way to prop them open
- Can be adjusted to open when greenhouse temperatures hit a certain threshold
- Open automatically during the day – great in summer if your mornings are still on the cool side
- Will stay closed if you have a cloudy day that doesn’t warm up your greenhouse enough
- Close automatically at night when the temperature drops
- Will stay open if nighttime temperatures do not drop sufficiently
- Are located where hot air gathers naturally at the roof vents
The automatic vent openers do cost some money. But in the end you can save a lot of money by not having plants perish when greenhouse temperatures hit extremes because you forgot to open the vents manually. And it save you a lot of time not having to open them in the morning (or later in the day) and close them again at nighttime.
Electric vs. Wax charged automatic vent openers
Electric automatic vent openers use an electric motor to open the windows in the morning and close them again at night. They require an external temperature sensor to tell them when the temperature reaches a preset level.
Since you have to rely on a power supply, whether it be batteries, solar cell or line power to power the motor, if anything goes wrong with the power source, your vents won’t open or close.
Non-electric automatic vent openers rely on a expandable wax (usually beeswax) that expands when heated and contracts when cooled. They do not require an external temperature sensor and are adjusted with a thumbscrew to set the temperature at which they open and close.
They are a bit more reliable than an electric system since you are not relying on an external power source or an external temperature sensor.
Here is a link to the non-electric ones I have installed in my greenhouse (3 of them): Lee Valley: Heat-Activated Window Opener
I recommend having at least two automatically controlled vents just in case one of the vent openers fails. I have three and wish I would have added more (and I may at some point).
For electric systems you can have two sources of power. But again have more than one vent as wiring or motors can fail, especially in the hot, humid environment of a greenhouse.
For more features (including this one) that I recommend all greenhouses to have, check out the post 7 Greenhouse Features to Make Your Greenhouse Better