Dedicated circuit for radiant floor heating?

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Old 08-04-15, 01:18 PM
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Dedicated circuit for radiant floor heating?

I'm adding a 2nd floor bathroom that will have radiant floor heating. I'll be running a new 20A circuit that will be dedicated entirely to the bathroom (outlets, lights, and fan). I'd like to avoid having to dedicate a second circuit for the floor heating if at all possible, as the manufacturer recommends.

It's a 20 sq. ft. heating mat, and it's only 2A at 120V, so a dedicated circuit seems like overkill, given that the bathroom circuit would be rated to support the heating element, an 1800W blowdryer, and the bathroom lights and fan all at the same time (and still not be maxed out). But maybe there's another rationale I'm missing? None of this will be inspected, so that's not a consideration for me (though the new bathroom is up to code in every other regard). I just am having trouble finding an actual reason for this requirement. Your collective wisdom is much appreciated!
 
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Old 08-04-15, 01:26 PM
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Unless the mfg requires a dedicated circuit, I believe you would be ok on the shared bathroom circuit. The NEC doesn't start to require dedicated circuits until you reach 50% capacity of the circuit, although in a bathroom that much fixed load probably wouldn't be a good design choice, even if legal. At ~200W I don't think this is a concern.

Make sure the heating mat is covered by GFCI protection, either through a receptacle, circuit breaker or thermostat.
 
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Old 08-04-15, 02:15 PM
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Thanks ibpooks. Definitely will make sure everything is GFCI protected.

Just to clarify--when you refer to 50% capacity, do you mean a dedicated circuit is required if the heating mat alone hits 50% capacity?
 
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Old 08-04-15, 02:26 PM
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Correct, if a fixed-in-place load is greater than 50% of a shared circuit capacity it's time to look at a dedicated circuit. That's not the only rule, but it's a good "trigger point" to keep in mind for when to check the code book more closely.

In this case I don't think it's a great guidepost since we know the other expected loads are 15A hair dryers. On a more "general purpose" circuit the other loads would be much smaller table lamps, TVs, computer charger, etc so the 50% method is a good approach. If your heater was getting into the 4-5 amp range I would more seriously consider the dedicated circuit.
 
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Old 08-04-15, 02:42 PM
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Makes perfect sense. Thanks much!
 
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