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I am looking at adding a Garage Heater to my garage on a 30A circuit. The heater is on a dedicated 240V circuit run on 10 AWG wiring with a 30A Siemens household breaker.

My heater is a Dr Infrared 6000W heater that is controlled by a wall mounted thermostat. In even the coldest temperatures, I anticipate it will not run for more than 20-35 minutes at a time before cycling off(garage is very well insulated, brand new energy efficient build).

The heater instructions recommend a 35A breaker and 8AWG wiring (to be 100% code compliant, I get it).

In my case, looking at it from watts (which I know is not the real way, but close), 30 AMPS is 7200 watts. My 6000 watt load represents 83% of the rated capacity. Just a bit over the 80%. Since in my application I am certain that my load is non-continuous (i.e. that heater will NEVER run for 3+ hours straight), am I safe to use on this circuit?

Would appreciate some opinions!

Thanks

  • How costly would re-running the wiring be? Also, does the heater specify it can be operated at 208V in addition to 240V? – ThreePhaseEel Nov 9 '18 at 2:30
  • I do have some options for other unused wiring circuits in my garage... they are not in ideal locations but i can run conduit to the right spots. I am not sure about the 208V question. – Jeff C Nov 9 '18 at 14:17
  • The reason for the 208 question is there may be a way to buck its power supply so it draws less than 24A. – Harper Nov 9 '18 at 16:31
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Nope

The heater designer was super dumb for designing a heater that is a skitsch over the 5760W limit for a continuous load on a 30A circuit. Most other heater manufacturers build to just shy of the continuous circuit limits, like the apocryphal 23A that almost every water heater and dryer is built to. But they may have built to 6000W because it sounds cooler than those (circuit limit compliant) 5500W heaters. That jibes with their strategy of selling direct to consumers via big-box stores.

Now you have to pay the price for that.

On the upside, your working circuit limit for your inevitable 40A circuit will be 7680W, so you can squeeze another 1500W heater in there.

You could go back to the heater manufacturer and say "are you super sure your device is 6000W and not, ahem, 5600W" like every other heater intended to work on a 30A breaker?

Probably not, though. You must use it in accordance with labeling and instructions, because that is how it was tested and approved (listed). So if it says use 8 AWG, there you go.

  • But it's possible (though highly unlikely) that the marketing name is rounded up from the true rating. Check the actual spec plate. – ratchet freak Nov 9 '18 at 12:24
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    In addition - NEC Article 424.3 (B) Branch Circuit Sizing, Fixed electric space-heating equipment and motors shall be considered continuous load. That's verbatim. So from a code standpoint there is no discussion about whether it is or is not continuous load. – Retired Master Electrician Nov 9 '18 at 13:27
  • Thank you for that, did not know that about it being automatically classified continuous load! Thank you for the answers! Luckily, my garage was built with a few extra circuits run in for future proofing. I do have a 6 gauge wiring run that was meant to be a secondary generator hookup that I can repurpose for the heater. For my curiosity, if the heater runs fine on the 30A circuit and does not trip the 30A breaker, isn't it safe to run? I know there is a difference between safe and code compliant, but asking for my curiosity. – Jeff C Nov 9 '18 at 14:05

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