Bath underfloor heat circuit

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GerryB

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woodbridge, ct. USA
A customer of mine just called and asked about heating the bath floor and said should he go with 120v or 240v. I told him it didn't matter because it was the same wire I would be pulling. But now I am thinking the last one I did was 120v and hardly drew anything. The HO had installed it with no way to get a home run to it, so I fed it from an existing circuit. Any advantage on the 240? The 120 ones I've done worked fine. This is a master bath but not exceptionally huge.
 
A lot depends on whether the underfloor heating is intended to just get the floor up near normal room temperature for foot comfort or whether it is intended to be a radiant heat source as the only heat source for the room. In the latter case the amount of power required will be significantly greater.
 
I don't see any advantage. Watts are watts and there is no power savings. The only advantage would be wire sizing and like you said that doesn't come into play here


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GoldDigger said:
A lot depends on whether the underfloor heating is intended to just get the floor up near normal room temperature for foot comfort or whether it is intended to be a radiant heat source as the only heat source for the room. In the latter case the amount of power required will be significantly greater.
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...to the tune of 4 times greater - for the same length of cable, one could install at different spacing and get different watt density for either voltage as well - so if looking at it from the perspective of how many watts of heat are wanted for the entire room you really need to figure out whether it is worth it to go with high watt or low watt density, maybe even multiple runs instead of one series through the room to maintain whatever density you want.

Consider that AFCI rules may be a factor if using 120 volts as well, where @ 240 volts they won't be.
 
ActionDave said:
I'd go 120V. I have about 10 sq' in my bath it draws an amp plus a little. The gfi is in the t stat, I don't know if it's the same for the 240V ones, but if it is I bet it costs more.
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Come 2017 NEC you will need AFCI for the 120 volt units in a bathroom, you do need them now in 2014 NEC in most any other room.
 
I bet you will see a surge of requests for 240v bathroom devices after the 2017 code cycle, towel warmers, heaters, in-floor heat, etc.
 
If it's a small enough area that you could run one circuit at 120v I'd do that provided the intent is for heating the floor and not the whole space, but if you have a large area 240v can obviously handle more square footage (of the same spec'd system). So you could save running 2 circuits of a 120v system with only installing one 240v system.
 
Any one know do the man. specs call for a dedicated circuit? I think they do, but like Action Dave said, a little over 1 amp is nothing. This is a new bathroom with a 20 amp circuit just serving the outlets in the bathroom. Second floor of a modular I'm working on and not that easy (but doable) to get a circuit up there.
 
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