Adding underfloor heating system - advice on circuit

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  #1  
Old 10-24-10, 06:40 AM
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Adding underfloor heating system - advice on circuit

I am adding an underfloor heating system to my bathroom. The system is rated at 600 watts at 120v (can I equate this to a 5 amp load?). The thermostat has a built-in GFCI.

I have two convenient options for a power source:

1) I have a 15a circuit for outlets in my unfinished basement which includes my work bench and an overhead 2-bulb 48" fluorescent light. This circuit is wired with 14-2 copper. On this circuit, I have 5 double gang boxes with two duplex outlets each (10 outlets total), another double gang box with one duplex outlet and one switch for the fluorescent light. Other than the occasional power tool at the work bench, none of the outlets are in use. The total wire length of this circuit is 180 feet. I would be extending it another 20 feet to reach the underfloor heating control.

2) I have a whirlpool tub with a 9.9 amp motor on a dedicated 20a circuit with 12-2 copper with a GFCI. This circuit also feeds a convenience outlet on a knee wall in the bathroom. The total wire length of this circuit is 50 feet. I would be extending it another 25 feet to reach the underfloor heating control.

Any recommendations on which I could/should use?
 
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Old 10-24-10, 02:39 PM
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I think I found a better method for Option 1, my circuit of basement outlets and workbench:

From the panel to the first outlet is 27 feet. From this location to the thermostat for the floor is 36 feet. Combined length is 63 feet (which includes all my vertical runs). Although this alternate new run is longer, I can avoid the voltage drop created by the 200 feet of wire if I were to attach to the end of the circuit.

I am in the US, Ohio, Franklin County, City of Columbus.
 
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Old 10-24-10, 03:17 PM
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I don't think you are allowed to feed anything in the bathroom from a circuit located outside a bathroom. I'll have to double check, however.

Why not run it off the same circuit as your bath lights or receptacle?
 
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Old 10-24-10, 09:09 PM
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Originally Posted by HotinOKC View Post
I don't think you are allowed to feed anything in the bathroom from a circuit located outside a bathroom. I'll have to double check, however.

Why not run it off the same circuit as your bath lights or receptacle?
I discovered my bathroom lights and fan are on the same circuit as my bedroom outlets and closet lights. This is from the original construction in 1998. For lights, I have:

two 3-light bars (60w max each) total = 360w
two cans (75w max each) total = 150w
fan .5a = 60w
closets two dual bulb fixtures, (60w max each) total = 240w
Light and Fan total = 810
Bedroom outlets = 8

All of this on a 15a breaker, probably 14-2 wire. Using an 80% reduction, the total permitted for this circuit is 1440 watts. My lights and fan are 810 which leaves 630w. If I add the 600 watt floor heating system, this would only leave me 30w for the 8 bedroom outlets thus the bathroom light circuit is not an option.

The bathroom outlets are dedicated to the bathroom and are on a 20a circuit providing 1920w (20a x 120v x.8). My wife's hair dryer is rated at 1875w. I am sure the hair dryer and the floor would be on at the same time as well as the toothbrush charger. Therefore, this circuit is not an option.

In my area, it appears the bathroom outlets need to be dedicated to the bathroom but the lights can be shared with other spaces. I am guessing the floor heating system would be considered more like a light fixture (fixed) versus a convenience outlet.

I also discovered my basement lights are shared with my dining room and living room outlets. This was a new build in 1998 so I assuming this is okay with the local code.
 
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Old 10-24-10, 10:40 PM
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The underfloor heating system does not need to be a circuit dedicated to the bathroom. It does, however, need to be able to supply a minimum of 125% of the full load current draw of the heating system plus 100% of the rest of the permanently connected load.
 
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Old 10-25-10, 08:24 AM
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It sounds like there are several things that the Code has required for years that was overlooked in the constuction of your house. The bathroom receptacle should have been on a 20 amp circuit fed by #12 wire. Lighting and fans could share that circuit as long as only that one bathroom was served. If other bathrooms shared the circuit it can only have receptacle loads, no fans or lights.

The dining room receptacles should not have been used to power the basement lighting.
 
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Old 10-25-10, 04:43 PM
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Originally Posted by Furd View Post
The underfloor heating system does not need to be a circuit dedicated to the bathroom. It does, however, need to be able to supply a minimum of 125% of the full load current draw of the heating system plus 100% of the rest of the permanently connected load.
That's what I have gathered from other information I have read. The underfloor heating will be the only permanent connected load on the circuit I am contemplating.

Thanks for the information,
 
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Old 10-25-10, 04:52 PM
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Originally Posted by pcboss View Post
It sounds like there are several things that the Code has required for years that was overlooked in the constuction of your house. The bathroom receptacle should have been on a 20 amp circuit fed by #12 wire. Lighting and fans could share that circuit as long as only that one bathroom was served. If other bathrooms shared the circuit it can only have receptacle loads, no fans or lights.

The dining room receptacles should not have been used to power the basement lighting.
You got me curious so I investigated each outlet a little close.

The bathroom receptacles (two of them and one is a GFCI) are on a 20amp breaker and, I assume, a #12 wire and is dedicated to this one bathroom.

Lights and fan in the bathroom share the lights in the closet and bedroom receptacles that are split with one outlet always hot (top?) and the other (bottom?) is controlled by a light switch.

The dining room and living room lights and outlets controlled by a light switch are on the same circuit as the basement light. The basement light switch is a 3-way with one in the living room at the top of the stairs and the other at the bottom of the stairs. The dining room and living receptacles that are not on a switch are not on this same circuit.

I believe what was done was to maximize the light circuits.

Thanks very much for the reply.
 
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Old 10-25-10, 05:27 PM
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Originally Posted by glt57 View Post
You got me curious so I investigated each outlet a little close.

The bathroom receptacles (two of them and one is a GFCI) are on a 20amp breaker and, I assume, a #12 wire and is dedicated to this one bathroom. If #12 this is good

Lights and fan in the bathroom share the lights in the closet and bedroom receptacles that are split with one outlet always hot (top?) and the other (bottom?) is controlled by a light switch. Sounds fine as long as not overloaded.

The dining room and living room lights and outlets controlled by a light switch are on the same circuit as the basement light. The basement light switch is a 3-way with one in the living room at the top of the stairs and the other at the bottom of the stairs. The dining room and living receptacles that are not on a switch are not on this same circuit. Good

I believe what was done was to maximize the light circuits.

Thanks very much for the reply.
I though the dining receptacle circuit had be incorrected tapped for part of the basement.
 
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