120V vs 240V for heated floors and also in general

[Aaron Fude]

Hi,

I'm a little confused about the whole 120V vs 240V things. More specifically, I'm now deciding whether to put in 120V or 240V mats to heat the tile in my bathroom. My electrician told me to "of course, put in 240V" because you then need a smaller current for the same amount of energy. Yeah - I understand that from my physics class - but so what? Is it safer? Is it more efficient? Does it work faster?

Further, I called the floor heat company and they told me that 120V is for up to 150 sq ft and 240V is for 150 sq ft to 300 sq ft. So I don't know which one to go with anymore.

Please shed some light on this issue. Thank you!

Aaron Fude

[HotRdd]

240 V will be cheaper to operate.

[Edwin Pawlowski]

As you double the volts, you half the amps. That means you can run smaller, less expensive, easier to work with wires. Operating cost will be the same.

The 150+ is 240V for the reasons described. You don't want to have to run #8 wires for the lower voltage units.

[Edwin Pawlowski]

How so? Watts is watts and you pay by watts.

[beecrofter]

240 uses less copper, skinnier wire costs less.

[dpb]

Installation cost, yes; operational cost, no (unless is grossly undersized so wire voltage drop is significant making wiring I^2R losses sufficient to not be ignored at the higher current of 120V).

[Chris Lewis]

According to Edwin Pawlowski :

Maybe. Eg: 10A at 120V requires #14 wire minimum. 5A at 240V also requires #14 minimum. So there's no particular "wire" advantage either way in that example. 240V needs another breaker and slot tho.

There's a very slight difference, depending on circumstances probably not worth caring about.

Which is true.

It's kind of like electric heaters. You can get 1500W ones for 120V. Plus all the plug-in ones. But anything over 1500W will almost always be 240V, even the plugin ones. Here they're giving the "switch point" in square feet.

If the installed price was the same for 120V vs 240V, and I had the room in the panel, I'd go with the 240V simply because the panel load is balanced.

In a floor application, the hazard is about the same either way.

[Sam E]

Pay to replace those big wires when you trip over them?

[John Gilmer]

The main advantage of the 120 volt system is that if you protect the circuit with a GFCI device, the protection will cost a small fraction of the cost of a 240 volt device. Most "line voltage" thermostats are 2 pole so that will not be an issue.

Otherwise, just about everything says go for the 240 volt system. Smaller wire, lower losses between the panel and the heater, less temptation to "tap" the supply line.

[kayostar]

responding to

kayostar wrote: I agree. The 240V would be the cheaper and more efficient to get in the long term.

[trader4]

The only difference in "long term" is the tiny difference in wasted energy that you get from running 2X the current when using 120V. That tiny loss is due to the small resistance in the wire, assuming the same gauge wire is used. Otherwise, the costs and issues are all there on day one. And IMO and without doing the math, it would take a very, very long time of running that small bathroom floor heater for those losses to amount to anything.

It would be helpful to also know how many watts this load actually is. But the core issues are:

Can you use smaller wire in this case when going with 240V? How long is that wiring and how much would you save? Does it need to be GFCI protected? As someone pointed out double pole GFCI is a lot more than a single pole. Have a panel slot for a double?