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?
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
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
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
AFAIK, 240V GFCIs measure the difference in current between the two hot legs.
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?
You can hang more electric heaters on a 240V circuit. Some heaters are
also too high a wattage for a 120V circuit.
If water is kept away from electrical connections on a "hydronic" heater
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
I think "hydornic" heaters operate at a lower temperature.
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.
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
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.
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.
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
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
I "think" hydronic is supposed to be safer because the heat is more spread
out and nothing gets very hot.
Electric heaters no matter what voltage are for all intents and purposes
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
As someone said 750 watts, at 120 volts is only around 6 amps. On 240 it
would be around 3 amps!
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'?
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
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.
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.
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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