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How to wire a fan to a thermostat? Answered

I have a fan for a greenhouse that I need to turn on at certain times to counteract the Texas heat, I was just wandering if I could just go to a garage sale and buy one then wire it to the power chord or is there a special small one that plugs into the wall socket. Also how would I go about instaling a thermostat in the greenhouse.



Best Answer 7 years ago

    Three parts to a thermostat system.
A) Temperature sensor with a human set trip temperature point
     Changes an impedance (lowers) to indicate when the set point occures
B) The energy to operate the system is 24VAC from a small transformer.
C) The fan control is a small 24vAC relay that can open and close contact
      to run a pump or fan that use 120VAC.

A plumbing shop can sell parts [B] & [C] of the system.
A hardware shop can sell part   [A]
Bell wire for inter connecting all 3 devices is available every where and
Radio Shack


3 years ago

FYI: Stego makes thermostat switches that don't require 24v. They just pass 120-240v in and out. The STS/STO model (part #s 01115.0-00, 01116.0-00, 01115.9-00, 01116.9-00) has adjustable temp setting, and about a 7-degree difference between when it clicks on and off. They have another model that is about 12-degree difference.

It's simple wiring. Insert this into the hot wire of the fan, leave the neutral return wire unbroken. The thermostat will open or close (depending on the model) when a temperature is reached, allowing power to flow through the fan.

You can get adjustable temperature switches that operate on 120 volts at Home Depot.

Here's a link to what you need.  If you can build it for less than $22 then you have a well stocked junk box.

Yeah, but that's the easy way.


7 years ago

A cheap on/off furnace thermostat would work but like Ork said its a 24 volt system. So you would need the little furnace transformer to go with it and then a relay to switch on the fan.
Here is an interesting thought--- If you could get an old furnace that is junked you could strip it down and use the fan and the relay that is already built into it. You could even attach duct work to it to vent more efficiently.

If you need a relay here are a bunch of them from Jameco.


A thermostat acts as a switch... but generally not a switch that can carry a lot of current or voltage. The standard setup involves a low-voltage loop (24V or less) through the thermostat, so that when the thermostat switch closes it activates a relay which in turn controls the circuit which powers the actual heating/cooling/fan/whatever

There probably are self-contained plug-in thermostats, but I couldn't tell ya where to get one without websearching... and you can do that as easily as I could.