240V vs. 120V electric baseboard heat? GFCI? hydronic?

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Can someone refresh my memory as to why 240V electric baseboard heaters are "more efficient" than 120V? In my application I am looking at install one 750W electric baseboard in a bathroom, on a dedicated 20A 120V circuit, but the heating man strongly suggests I use a 240V model. Problem is the breaker box is completely full, and I'd have to run a subpanel just for this circuit if we go 240V.
My other concern was GFCI protection - at 120V I could install a GFCI breaker in the panel to protect this heater circuit -- do they even make 240V GFCI's for the panel (GE)? I am a little bit worried about someone splashing water from the sink or a toilet overflow going into the electric baseboard heater -- the baseboard will be within inches of each.
Last item - electric "hydronic" baseboard sounds better than the standard electric baseboards - more even temperature - but I also saw a website say the hydronic units were "safer" - why? because the heating element is enclosed in a fluid tube and not exposed?
Thanks.
-- Paul
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higher voltages usually make heat faster for this discussion. As for putting a baseboard heater in a bathroom................. Have you recently taken out a lot of life insurance on the kids, SO?
There are 240v gfci's available from the manufactures. Since a gfci works with a neutral what exactly are you thinking of gaining? Safety,,, nope...
Your bathroom your design. Maybe I will be hearing from you on the 10 o'clock news.
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How does 240v / 10A "make heat faster" than 120v / 20A?
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Old wives tale. 750 watts is 750 watts. Neither faster nor more efficient at higher voltage. Conversion is 3.413 BTUs per watt, no matter the voltage. You can use a smaller wire size with a higher voltage unit but at 750 watts even a #14 would be enough for either voltage.
Stretch
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No. It's 3.413 Btu PER HOUR per watt or 3.413 Btu per watt-HOUR, since watts are power and Btus are energy, ie power times time.
Nick
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stretch wrote:

Power factor(efficiency) is better at higher voltage? Tony
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Hi,
No.
John.
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I think 220 volt gfci's work as well as the 110. Exception is that neutral not used - current in both power lines must be equal.
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-------------------snipped-------------------

quoted from the Siemans link "To protect against electrical shock, Siemens GFCIs continuously monitor the difference in current between the hot and neutral conductors."
Since the heater does not have a neutral how will a GFCI provide any increased safety?
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AFAIK, 240V GFCIs measure the difference in current between the two hot legs.
-- Regards, Doug Miller (alphageek at milmac dot com)
Nobody ever left footprints in the sands of time by sitting on his butt. And who wants to leave buttprints in the sands of time?
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wrote:

They're *not* more energy-efficient. A 240V heater will produce more heat than a 120V heater of the same physical size, but it will consume proportionately more power as well.

IMO, running a new 240V circuit to power a single 750W heater is nuts. 750W at 120V is 6.25A, well within the capacity of a 15A 120V circuit.

You could even install a GFCI outlet in the bathroom, and feed the heater from that.

Yes, but they're pricy.

GFCI sounds like a good idea, then. You might check local code to see if it even permits placement of an electric heater that close to fixtures.

Yes.
-- Regards, Doug Miller (alphageek at milmac dot com)
Nobody ever left footprints in the sands of time by sitting on his butt. And who wants to leave buttprints in the sands of time?
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Paul wrote:

also too high a wattage for a 120V circuit.

and the heater is well grounded it is probably safe. Wiring a heater downstream from a GFCI outlet would be a lot cheaper and avoid another breaker.

If a flamable item contacts and blocks air circulation on a 'normal' electric heater the temperature will rise since heat is still being produced but not carried away and the item could catch fire. Even if the heater has a safety thermostat it is hard to protect the whole length of the element. A hydronic heater has an electric element heat water in a large-surface-area tube. The water is all at about the same temperature.
I think, without looking it up, that you can't install an outlet above a 'normal' baseboard heater (because of high temperature damage to cord insulation) but you can above a "hydronic" heater.
Bud--
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240 V. Heaters are more efficient in that there is less voltage drop (=wasted power) in the line to the cb panel with the higher voltage.
Since the voltage is double, the ability of the 240 V. circuit has a higher capacity to deliver more current for a given resistance than at 120 V. The power output is I squared x R for both. (R will be specified at a certain value for 120 V. heaters and a different value for 240 V. heaters - In general, they are designed with different heating elements that are matched to the input voltage).
Although you can buy high wattage 120 V. heaters, the 240 volt versions are generally going to be more robust, heat up the room faster, and have a higher capacity (wattage).
A double-ganged 240 V. GFCI is expensive and generally not used in these applications. Safety is provided by the regular grounding wire of the heater. Here is an example of a two-pole GFCI that is used for hot tubs:
http://www.sea.siemens.com/reselec/product/rzgfci.html
The hydronic electric heaters are similar to the oil-filled deLongi portable units. They heat up a little bit slower, but the heat delivered stays fairly constant as they continue to give off heat even when the thermostat cycles off. Use this model if you prefer a gentle heat delivered at a constant rate.
The purely radiant electric heaters (with the glowing red coils) stop delivering heat as soon as the thermostat cycles off.
Beachcomber
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If by "circuit" you mean "the wires in the wall," you might more clearly say:
Since the voltage is double, the ability of the 240 V. circuit has a higher capacity to deliver more power for a given resistance than at 120 V.
Nick
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replying to Beachcomber, luis gomez wrote: 240 less current 120 more current . call an lice electrician
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Paul wrote:

In general as others have said already, 240V is more efficient, but for your application since you already have a dedicated 120v 20A outlet, and no more room in your breaker panel, you should be fine with the 750W heater.
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Lots of interesting opinions!
If you wanted a 2400w heater, 240v would definitely be the way to go. For a 750w it makes no difference at all. In fact, it doesn't even have to be a dedicated line as long as you don't put anything big on it. Geez, it is only 6a.
I "think" hydronic is supposed to be safer because the heat is more spread out and nothing gets very hot.
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Electric heaters no matter what voltage are for all intents and purposes 100% efficient. In other words they turn all the electricity fed into them into heat.
So whether 240 or 120 volts is not material from point of view of amount of heat and nothing to do with efficiency!
The discussion about 240 versus 120 sounds more about the practicality of wiring with no availability of fuse or breaker positions in an already full panel.
As someone said 750 watts, at 120 volts is only around 6 amps. On 240 it would be around 3 amps! See addendum:
But whether electrical codes allow you to mix an electric heater and outlets on the same 120 volt circuit is a question!
FWIW: Our bathroom is small and without a window. The bathroom heater located under the towel rail is 240 volt 500 watt, it is one of several each with it's own room thermostat on a 20 amp electric heaters only circuit. It complies with our codes; the heater being completely enclosed except for upper and lower small air vents through which you could put a pencil but not a finger (and a child's finger would not be long enough to reach the heater element). Also it is GROUNDED and that grounding is bonded to the copper plumbing and fixtures. The bathroom shaver outlet is on a separate circuit and is a GFCI type. We chose that type (GE type) heater 35 years for safety after other home's, more open types, had resulted in scorched bedclothes, but fortunately no fires.
Oh btw; we also have six 40 watt bulbs in a fixture above the mirror. If left on these contribute noticeably to the heating of the bathroom.
As a completely separate issue that full panel should worry. Also if you DID decide to install a subpanel IT would itself need a (probably a double pole) breaker in the main panel to supply it! Your panel, due to additions and changes, may be 'at capacity'?
Addendum:
1000 watts @ 240v = 4.2 amps 750 watts @ 240v = 3.1 amps 500 watts @ 240v = 2.1 amps
1000 watts @ 120v = 8.4 amps 750 watts @ 120v = 6.2 amps 500 watts @ 120v= 4.2 amps
At electricity cost of 10 cents per kilowatt hour; if the heater was 'on' continuously, both 1000 watt heaters would cost 10 cents per hour.
For improbability and to further demonstrate volts/watts and amps! Imagine a 12 volt 250 watt heater? 250/12 = 21 amps. Enough to drain a car battery in average condition in less than two to three hours! Oops; car won't start!
Note: For another comparison a large microwave oven plugged into a 120 volt outlet can require 1200 watts (1200/120 = 10 amps). Usually, for typical m.wave oven use, for a fairly short period of time.
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You pay for watts, not for volts. The 220v, you can use smaller wire when installing. Not more energy efficient.
I don't know about 220 volt GFCI.
"Hydronic" I thought meant that it heats water, and then the hot water goes to the area to be heated. It's still electric heat.
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Christopher A. Young
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Stormin Mormon wrote:

You can use smaller wire but you would probably increase the voltage drop across the wire. If you compare lets say a 110V A/C that uses 10 amps on a 12 guage wire, that same A/C using 220V would use only 5 amps on 12 guage wire. In theory, they both use the same watts but then you factor in the voltage drop, the 110V A/C would have twice the voltage loss than the 220V unit. The 110V unit would be working harder to cool a room. So in a way the 220V is more efficient.
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