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I have the unenviable task of replacing a floor (or three) in my home in the coming weeks/months. We are considering a mix of tile and solid hardwood.

It appears that it is possible to retrofit in-floor heating (electric). And the price isn't so fantastic that it's immediately off the table either. However, I think I will be constrained by just how many open slots for breakers are left in my panel.

One option available at Home Depot's web page says that it covers an area of 3' x 10ft'. I would need six of these alone just for my living room, with other rooms probably tripling or quadrupling that figure.

The documentation for that product suggests that I need at least 10A of circuit per 100sqft of flooring. Will I really need a 30A circuit just for the living room alone (roughly 250 sq ft)? When McMansions do this stuff, are they setting aside 300A of power just for their 3000 sq ft suburban castle? (Hell, isn't 240A service normal, do they have an entire second panel set aside for this stuff?) Are they only using the hydronic systems? Can someone walk me through the rough estimates to see if this is viable or not? What are the rules of thumb? I expect to confirm that this isn't a feasible wish, so don't feel reluctant to disappoint.

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    Resistive heat uses a lot of power, and electric heated floors are retrofitted to relatively small areas, not everywhere in a 3000 sqft home. If you wanted large areas you would probably be better served with a hot water based floor heat system. Also it doesn't need to get that close to walls or under cabinets so heated sqft will be less than the area of the room.
    – JPhi1618
    Commented Nov 3, 2021 at 20:21
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    Price might be decent to put in, but have to be concern about the price to use. 10 amps at 240 volts is 2400 watts by ten hours per day comes to 24 KWs per day. can add up. Going easy on amount of time used per day, your use might be more or less. They say in floor heating is a nice heat.
    – crip659
    Commented Nov 3, 2021 at 21:08
  • Yes, 400A service (“CL320”, 320A continuous usable) is normal for large houses these days.
    – nobody
    Commented May 9 at 1:23

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Just say "no" to giant toasters.

Resistance electric heat, whether buried inside an air handler, installed in baseboards in every room, or in a small portable heater, is really just a giant toaster, which makes it generally very expensive to run. For an actual toaster, that's not a problem - you use it for 5 minutes a day. A portable supplemental temporary heater isn't so bad, if it is used as a supplement (e.g., heat your feet under your desk at the start of the day) and not in place of a permanent, efficient, heating system.

Generally speaking, a natural gas heating system (e.g., forced air furnace) or a fueled hot water system is much more efficient by the time you factor in fuel costs vs. electricity costs. While resistance heat is technically 100% efficient, there is also the generation efficiency to consider, which is factored into the cost of the electricity.

Even more efficient is a heat pump. Heat pumps used to be quite limited in the old days, but have become more efficient in general and much better able to handle low outside temperatures.

So it is quite likely that large homes with lots of in-floor heating are using hydronic systems powered by natural gas. If you want to heat a small area - e.g., a bathroom floor - with electric resistance heat, that is quite reasonable - and similar to heating up a bathroom using a heat/fan in the ceiling. Heating an entire, large, house with resistance floor heating just doesn't make sense - that would be even worse than on-demand electric water heaters, which can easily use 100A or more.

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