Wiring Radiant Heat

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Old 02-03-06, 06:40 AM
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Wiring Radiant Heat

I have some confidence in my tiling skills but not much experience with electricity. My sigificant other says no tile floor in our kitchen (on a concrete slab) without electric radiant heat. So, I need some guidance, please.

The old house that we live in has a an old fuse box panel that is rated at 100 amps (General Switch Corp-100 amps-120-240AC-poles 3SN). I assumed that with the older wiring that there would be some limitations creating another 240 volt circuit for the radiant heat so I cut the square footage of the floor to be heated back so that it can run on a 120 volt circuit.

There is a 120 volt/15amp circuit that is convient to where I would like to place the programmable thermostat. It has most of the kitchen lights on it and adding in the the 960 watts from the radiant heat brings the total load to 1280 watts (below the safe capacity of 1440 watts).

Am I right in my thinking I can add the radiant heat to this to that circuit?
What am I not thinking of?
Any considerations for water/flooding with radiant heat? (There are two hot water heaters next to, and on the same level as the kitchen floor.)
I have read the information for installing and wiring the radiant heat and it seems doable for someone with limited electrical experience. Let me know if you disagree.

Thanks!
 
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Old 02-03-06, 06:49 AM
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Originally Posted by Mark Smith
The old house that we live in has a an old fuse box panel that is rated at 100 amps (General Switch Corp-100 amps-120-240AC-poles 3SN). I assumed that with the older wiring that there would be some limitations creating another 240 volt circuit for the radiant heat so I cut the square footage of the floor to be heated back so that it can run on a 120 volt circuit.
In my opinion this is a poor reason to not use a 240 volt circuit. Since you have fuses, an upgrade is in order anyway so that you will have breakers. Your insurance company MAY make you eventually switch anyway, so why not do it now.

I would not add radiant heat to a general purpose circuit, especially is this circuit has any receptacles on it. The potential to overload the circuit is too great.

When you did your calculation, did you calculate based on the maximum wattage light bulb per fixture, and not on what YOU have installed?
 
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Old 02-03-06, 07:35 AM
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So, experts, this is definitely too big a system to tie in with an existing general purpose circuit, but if it were smaller, say 200 watts, would it be acceptable? I've always thought that any type of electric heating needed to be on a dedicated circuit.

With most of the radiant systems I'm familiar with, you'd have to get really big to need 240V. That large a system might have a noticeable impact on the electric bill so downsizing it was a good idea in other ways anyhow.

To address the water concern, most of the radiant floor thermostats available have built in GFCI protection. If it isn't built in, it has to be provided in the circuit prior to the thermostat. All electric radiant floors require this.

Additional advice: Some of the manufacturers claim you can install the system without a thermostat and just switch it on when needed. Don't. Not only should you install a thermostat designed for radiant heating, with a floor sensor, it would also be advisable to go with one that has automatic setback so you don't need to leave it on all the time and can set it to turn on a couple hours before you need it. You won't be pleased if you try to turn in on manually when needed. By the time you feel the warmth, you won't need it anymore. Also, if there's any way you can get some insulation board between the slab and the heating wire, it will greatly improve your satisfaction and electric bill.

Doug M.
 
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Old 02-03-06, 10:33 AM
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Thanks all for the quick response!

There are no receptacles on the circuit but my calculation was on the wattage installed not the maximum wattage permitted so I will refigure. Most likely that will put it over the safe capacity so we will consider the upgrade and dedicated line you suggested.
 
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Old 02-03-06, 02:02 PM
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Originally Posted by dougm
I've always thought that any type of electric heating needed to be on a dedicated circuit.
That would be nice. But if cord-and-plug connected, I'm afraid that it can go in any g.p. receptacle.
 
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