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I just purchased a garage heater from my local big box hardware store and I am planing to set it up, but had a couple questions I'd like to run by the experts around here.

Firstly, I originally planned to set up this heater (like I've done in other garages) via a contactor. But I've only set these up in that past in larger garages where it warranted multiple units that led to a single thermostat control. Wire up each unit to their own 30 amp breaker and the thermostat to a 15 that controls the contactor.

In my fairly small garage I don't need multiple units so I was thinking of just setting it up with a thermostat, like this one. I am curious:

  • Can I use this thermostat which is rated at a maximum 22amps on a 30 amp breaker (considering the heater is rated at a max of 20amps)? A friend in the field was saying that he wouldn't put a 22amp thermostat on a 30 amp breaker, even though the heater only uses 20 amps because in the rare instance the heater pulls more than 22 amps (which wouldn't trip the breaker) it could heater up the thermostat and be bad.
  • Can I use this type of switch for a 240v unit? Like this? My rational for this was to, instead of using a separate thermostat, use the built-in thermostat on the heating unit but have a conveniently position on/off switch so I don't have to reach up to the heating unit (mounted from ceiling) or go into the panel every time I want to turn the unit on/off.
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The start up current of the heater probably is a bit over 20 amps (like 25) for up to a minute. Once it heats up, its load should be at 20.833 amps.

For less than an hour, that is an acceptable load, but heating equipment wiring must be rated for continuous load according to the NEC.

Either get a lower rated heater instead, or use a contactor. The contactor also provides the benefit of allowing a smart thermostat.

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From the Installation Instructions

If a remote line voltage thermostat is used it should be rated for higher than the amp load of the heater connected.

The instructions list your model at 20 amperes.

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However, NEC requires conductors (210.19(A)(1)(a)) and overcurrent devices (210.20) feeding continuous loads to be rated 125% of the load. So the breaker, the conductors, and the thermostat should be rated for at least 25 amperes. Which is why a 30 ampere breaker, and 10 AWG copper is required as per the instructions.

  • In the end I decided to use the 30amp switch and the built in thermo for the unit. I actually set up a 2 heater unit via a contactor in a big garage last week with my electrician buddy and I really don't think it's worth it to do that in my small garage. – justinw Oct 24 '14 at 15:33

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