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I have a gas ceiling mounted furnace for my garage.

I want to set my garage at 35-40° F (1-4° C).

Is there a special thermostat to control furnace at that low temp? (I've seen one works as low as 50° F (10° C), but not as low as 35-40° F)

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I don't think so- But it is easy to make on using a simple PIC controller. I can make you one. It uses a Temperature sensor(0.01C sensitivity and accuracy), PIC and a Solid State Relay. It can do other things too. about 50USD.The simplest form is controlled via USB programming. Using an LCD and Buttons starts pushing the price upwards but i can do whatever you want it to. Even control via internet or mobile text messages? – ppumkin Oct 20 '11 at 10:55
If asked today, this would be closed as a shopping question. But since others may find the content useful, I'm only locking it. – BMitch Feb 1 '14 at 11:58

Yes. One example is the Honeywell CT50K1028/E which is your basic low voltage thermostat it goes down to 35 F. I'm pretty sure it will work for your application. No hacking or electronics work reqired. There are others. Do a search for " Garage thermostat"

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They make them for controlling electric baseboards. Check the wiring requirements for your furnace to see what the thermostat needs to support. For example, this probably wouldn't support running just the fan:


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You may be able to hack something together with a refrigerator thermostat. You'd have to do a little tinkering though, since it would do the opposite of what you want to do. When the temperature rises above a certain point, the fridge thermostat will cue the appliance/heater to turn on. If you can figure out how to reverse the process, this could be a possible solution.

If you don't want to pay $50 for a thermostat that you may or may not be able to make work for your solution, Hack A Day featured how to build one a few years ago. It may also be easier just to edit the code to make the thermostat turn on the heater when the temperature drops below a threshold rather than above it. (That is, if you're familiar with that sort of thing.)

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That hack a day is good n cheap.. but you there is no way to set variability in temperatures.. unless you resolder some resistors to the desired one. But good post! – ppumkin Oct 21 '11 at 8:54
If hacking, an Arduino plus temperature sensor chip would work. arduino.cc I expect using method method would be a major building code violation. – Wayfaring Stranger Feb 1 '14 at 16:18

My Honeywell RTH7500D can go down to 4.5° C, if that is close enough for you.

enter image description here

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