Pros and Cons of 240 or 120 floor heat ?

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Buck Parrish

Buck Parrish

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What are the pros and cons of using 120 volts or 240 volts to power residential floor heat? The resistants' is about 22 ohms. I was just curious, the prints say 120. I thought it would heat faster on 240.
 
On 120 , Do you put the neutral on the thermostat, too.
Line 1 Black Line 2 white?
Or do you make the neutral by-pass the thermostat?
 
180507-2243 EDT

At 120 V 22 ohms is about 654 W, and four times this at 240. Neither will do much heating.

What stray magnetic field is created?

.
 
Buck Parrish said:
On 120 , Do you put the neutral on the thermostat, too.
Line 1 Black Line 2 white?
Or do you make the neutral by-pass the thermostat?
Click to expand...
That would entirely depend on the design of the thermostat. Most electronic ones would need the neutral just to power the electronics even if they don't switch the neutral.

Latest NEC and dwellings - 120 volt needs to be AFCI protected in most instances.

Which heats faster - well if you put in say 1000 watts of heat - won't matter 1000 watts is 1000 watts, just draws twice as many amps at 120 then at 240, still draws 1 kilowatt hour for every hour it runs.

Now if you put in 1000 watts of 120 volt rated heat cable and apply 240 volts to it - it will draw 4000 watts - will heat much faster - will likely burn out in no time also.
 
When we had our master bathroom remodeled a few years ago, we included in-floor heating. We have one circuit that feeds everything in that bathroom, including the floor heat, the lights, and the fan, and that feeds nothing outside the bathroom. The floor heat is therefore 120 volts. It works so well that the cats love sleeping on a rug in that bathroom. I wasn't there when the electrician connected it, so I can't tell you anything about the wiring.
 
gar said:
180507-2243 EDT

At 120 V 22 ohms is about 654 W, and four times this at 240. Neither will do much heating.

What stray magnetic field is created?

.
Click to expand...
1) the total wattage is not the only thing in this story. 0.25watt on a surface area of 0.01in^2 will about burn you very fast. 4000watt over say 200sq.ft. is 20w/ft^2, which is a decent amount of heat. but if ambient is say -20F then 20w/ft^2 may only keep the bottom of bare foot warm. power flux and operating temps and room sizing are important. but remember, even in a room that is 20ft high, you only need to heat and cool to about the 1st 7ft, because we rarely hang out in any room above 7ft, etc.
2) AC60Hz, a stray alternating magnetic field is created 60x/sec. you have amps, you have EM fields. what it looks like in spatial depends on if its homogeneous heating mat, or a wire that loops around.

3) why would 240v be better than 120v? none in terms of heating because heat is based on DC ohms and amps. 120v is "safer" (lower voltage) than 240.
 
kwired said:
That would entirely depend on the design of the thermostat. Most electronic ones would need the neutral just to power the electronics even if they don't switch the neutral.

Latest NEC and dwellings - 120 volt needs to be AFCI protected in most instances.

Which heats faster - well if you put in say 1000 watts of heat - won't matter 1000 watts is 1000 watts, just draws twice as many amps at 120 then at 240, still draws 1 kilowatt hour for every hour it runs.

Now if you put in 1000 watts of 120 volt rated heat cable and apply 240 volts to it - it will draw 4000 watts - will heat much faster - will likely burn out in no time also.
Click to expand...

If you apply twice the voltage to a resistive element it will likely break down the insulation, cause a ground fault and possibly start a fire.


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Pros and Cons of 240 or 120 floor heat ?

120v is "safer" (lower voltage) than 240.
Click to expand...

It’s still 120 volts to ground. There’s virtually no difference in safety. Voltage drop is substantially reduced at 240 though


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DrSparks said:
It’s still 120 volts to ground. There’s virtually no difference in safety. Voltage drop is substantially reduced at 240 though


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Click to expand...

or 240 end to end.
voltage drop should be 120v end to end if its on 120v
voltage drop should be 240v end to end if its on 240v

perhaps i just not getting what you mean by voltage drop
 
FionaZuppa said:
or 240 end to end.
voltage drop should be 120v end to end if its on 120v
voltage drop should be 240v end to end if its on 240v

perhaps i just not getting what you mean by voltage drop
Click to expand...
For the same wattage element the current will be 1/2 for the 240V circuit compared to the 120V circuit. That means twice the voltage drop in the supply wiring (if same size wire) and the power wasted in that wiring will be four times that in the 240V circuit.

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FionaZuppa said:
2) AC60Hz, a stray alternating magnetic field is created 60x/sec. you have amps, you have EM fields. what it looks like in spatial depends on if its homogeneous heating mat, or a wire that loops around.
Click to expand...

Aren't these floor heating elements coaxial, with the current returning on the outer braid so both connections are at one end? That's what I've seen. That design has no net magnetic field outside the cable itself.
 
DrSparks said:
It’s still 120 volts to ground. There’s virtually no difference in safety. Voltage drop is substantially reduced at 240 though
Click to expand...
Yes, on the safety aspect. And yes, lower voltage drop if you used the same size conductor. OTOH, you might choose to use smaller conductors and save cost.
 
DrSparks said:
If you apply twice the voltage to a resistive element it will likely break down the insulation, cause a ground fault and possibly start a fire.


Sent from my iPhone using Tapatalk
Click to expand...
Has to be something grounded (with low enough resistance) in close proximity to fault to, if not the conductive portion of element likely heats up to a point it melts somewhere and eventually leaves you with open circuit condition.

Typical bathroom ceramic tile floor likely has high enough resistance to ground it won't trip OCPD if it faults - might in some cases have low enough resistance to trip a GFCI though.
 
GoldDigger said:
For the same wattage element the current will be 1/2 for the 240V circuit compared to the 120V circuit. That means twice the voltage drop in the supply wiring (if same size wire) and the power wasted in that wiring will be four times that in the 240V circuit.

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Click to expand...
but OP said its not fixed wattage, more like fixed load.
in that case you'll get 2x the amps on ckt wiring, therefore 4x wasted heat in ckt wiring (if same size wire as you say).

to half the amps you would need four 22ohm elements in series using 240v to get same wattage as 120-22ohms.
 
mpoulton said:
Aren't these floor heating elements coaxial, with the current returning on the outer braid so both connections are at one end? That's what I've seen. That design has no net magnetic field outside the cable itself.
Click to expand...
well, i suspect not. EM fields attenuate as a function of radius. the EM fields from each conductor of the do not hit each other at exactly |B|-|-B|, etc. nearly cancel each other out depending on geometry of the coax, is a better answer. would this net be of concern, likely not. ~5A on one wire has net that would not likely be of concern, but there is net. :thumbsup:
 
Besoeker said:
A resistance value was all he gave.
Click to expand...

fixed load, 'er ?

22ohms is 22ohms, doesnt matter if i hook that to 9vdc batt, or 14kV AC xfrmer.

hence, that load going from 120v to 240v will incur 2x amps or 4x the wattage across any DC ohms in the ckt end to end. obviously heating ckt wire that is not under the floor does not help in heating the room.
 
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