The first thing a backyard greenhouse grower has to understand about a greenhouse thermostat is that regular house thermostats are almost useless in the greenhouse environment.
There are simply too many things to go wrong with a house thermostat in this greenhouse environment so yes, specialized equipment is expensive and yes, you can use house rated thermostats. But, it’s a big but, the breakdown rate is high if you’re using house thermostats and you simply don’t want a breakdown on a cold spring night when frost wants to whack your tender plants.
To begin with, the high humidity corrodes electronic components very quickly and unless the thermostat is engineered to handle these conditions, it may only last 9-12 months before it deteriorates.
The second characteristic is one of accuracy. Normal household thermostats work with a margin of error of 3 degrees (the better ones are more accurate) but in a greenhouse where heating costs are large, a 3 degree difference can be a very expensive one. Mind you, if you have a lot of money, then this isn’t going to be an issue for you. 🙂
Solutions to Look For
I always bought a commercial grade greenhouse thermostat designed for either greenhouse or industrial applications.
These lasted for years and were trouble free in the moist, humid and fluctuating temperatures of the greenhouse.
And yes, they are way more expensive than the household varieties but you only need a cheap one to quit on a cold night to discover why you want to spend a lot of money on a good one.
There’s nothing quite like going out to the greenhouse to discover your plants have turned into what we call”plantsicles” to justify the extra expense of good equipment.
As an aside, I often used specialty barn thermostats available from farm supply dealers as the electronics of these are comparable to specialty greenhouse thermostats in both longevity and accuracy.
They were also easier to find (and somewhat less expensive) in our local area. I note the Internet has made finding greenhouse equipment far easier now than just a few short years ago.
Please understand the volume of air these units move means that variable speed thermostats are not a great idea – you want an all or nothing kind of thermostat for a high-volume greenhouse fan (or they’ll burn out faster with a cheaper multi-stage electronic unit)
I always had qualified electricians in to wire my greenhouses (and my house as well I note) Please understand that you do have to understand the difference between 12 volt house thermostats and commercial level fans that use controllers capable of handling 120 volts.
Thermostats used for heating typically work on 12 volts while cooling thermostats usually work on 120 volts.
Do not mix these up as you’ll burn out your heating thermostat very quickly if you use it to directly control a cooling fan.
Follow the installation instructions carefully
Greenhouse thermostats in a wide range of price points.