My girlfriend is crazy about making bread. However, as the temperature is often very cold around here, I would like to make her a box in which the temperature can be controlled.

I have purchased a thermostat and have figured out how to wire it to a heat from a heat lamp (simply breaking the circuit and putting the thermostat inbetween).

I would also use a metal box as housing. Is there anything else I should be aware of? I have zero experience wiring AC power.

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    Are you using a line voltage thermostat? Most thermostats (in the US anyway) use low voltage (24v), to control relays which turn the heat on/off. If you hook a 24v thermostat to line voltage, the thermostat will work for about 1 second (mostly as a spark emitter). – Tester101 Dec 9 '11 at 13:18
  • A diagram of your wiring, and some more information would make this question better. – Tester101 Dec 9 '11 at 13:19
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    Even a link to the thermostat you're using would help. – gregmac Dec 9 '11 at 14:54
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    Many fires are started by bad heaters. A hand-built auto-on-off heater is much worse - it has no designed or tested safety switches. You should really consult an electrician. – Nicole Dec 13 '11 at 0:02
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    You should use a GFI breaker on that circuit and be sure to ground the metal box. – Richard Raustad Jul 16 '13 at 0:49

Without AC wiring experience, I can't recommend that you do this. A better suggestion would be to use a space heater in a closed off space (no flammable materials and have a smoke detector if you're going to leave it unattended).

However, if you ignore that, then at least consider the following.

Use an AFCI protected outlet. The arc-fault breakers will trip when things start sparking, hopefully before they burst into flames.

Make sure your switch is designed for your AC voltage. Wiring for HVAC thermostats are usually 24v. To use one of these, you'd need a 24v transformer and some kind of solenoid/relay to safely close the 120v circuit. They also make thermostats designed for 120v AC power, which would be a better option.

  • I think a space heater would put out way too much heat for this. – Adam Jaskiewicz Dec 12 '11 at 1:39
  • @AdamJaskiewicz, depends on the size of the space (they all have clearance requirements). If they are really crazy about bread, then a small room (perhaps the kitchen) would make sense to heat. My biggest concern is to steer someone away from plugging a home made gadget into an outlet when they have little experience. Those UL ratings have a purpose. – BMitch Dec 12 '11 at 1:56
  • I was picturing something like a proofing box, i.e., big enough to proof a few loaves. Something like that would be about the size of an oven, maybe a little bigger. – Adam Jaskiewicz Dec 12 '11 at 12:38
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    @JeffFerland: AFCI was intentional. GFCI doesn't detect an arc in a wire like you would have when shorting out a bad connection. Think of AFCI as preventing fires while GFCI prevents electrocution, and with this question, I'm more concerned with fire. – BMitch Dec 14 '11 at 20:53
  • @BMitch Ah, good to know! Please edit it back! – Jeff Ferland Dec 14 '11 at 20:53

I would use a thermostat like this, which is designed for controlling a window air conditioner or space heater. Then you can use a small clamp-on dish style light fixture that plugs right into the thermostat, no wiring required. Just use an extension cord so that you can put the thermostat inside the proofing box.


(a bit more complex) but...

You can use an Arduino, a 5v to 120v relay, temp sensor and a heater.

Spark Fun: Controllable Power Outlet has a nice write up on how to use a 5v relay with an arduino and a power outlet.

Spark Fun: One Wire Digital Temperature Sensor for a temp sensor

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    You qualify a solution that uses a microcontroller and a half-dozen other parts and requires writing code as just a "bit more complex"?? :) – gregmac Dec 9 '11 at 17:53
  • Thanks for your help. I actually have an arduino and can code, so maybe that's also a good solution. The schematics for the thermostat are here: finder-relais.net/en/finder-relays-series-7T.pdf It's the first model (7T. – Ray Dec 9 '11 at 18:08

I believe something like this Duct Stat Plug In Temperature Sensitive Switch might work. You can also google for 'temperature controlled switch'. Something similar may be those heat rocks used in lizard habitats or more complex may be the switches greenhouses use to open and close their windows.


There is a SIMPLE answer to this. Go to Home Depot. Buy a 120 volt thermostat that is typically used in wiring an in-wall 120 volt electric heater. (like a "Cadet" Heater.) These t-stats are a piece of cake to install. They install IN-LINE with the hot wire. (Do NOT connect it to the Hot and Ground wires) Read the directions....they are very clear. You set the thermostat to whatever temperature you want. It comes "ON" when the temp drops below your setting. It goes "OFF" when the thermostat reaches the temperature that you set. These are very reliable and accurate thermostats.

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    The OP mentions they already have the thermostat. – ChrisF Feb 18 '13 at 12:07

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