Chet is actually correct, although it may be couterintuitive. A
heater is a pure resistive load and follows Ohm's Law, V = IR. Since
the resistance R of the heater is fixed, if you double the voltage
applied, you'll double the current drawn as well. As to power, since
P = IV, when both I and V are doubled, the power P is quadrupled. This
is where the 4 times comes from.
Of course, since the heater is providing 4 times as much power, it
only has to run 1/4 of the time to deliver a certain amount of energy.
This is why it will heat up faster.
I was considering that, which is why I did not respond the first time.
It is also why I said "I am not sure what you are saying, but it seems you
are saying.." I agree with what you say and, it appears, what Chet was
trying to say, but I did not read it as he intended.
BTW In my head, my quick consideration of what was said, I did consider
the constant resistance and the increased current, but I did not factor in
the higher voltage. The more obvious of the two factors.
So sorry Chet. It was my fault. Of course I would assume a unit
designed for 240 would not have the same heater elements as one designed for
the same use but for 120.
The resistance remains the same. Even if you want to nitpick, because
it is water cooled the temperature coefficient doesn't matter. If you
double the voltage, the current also doubles -- Ohm's law.
(voltage x 2) x (current x 2) = power x 4.
Basically, when you operate a 240V heating element at 120V, it produces
1/4 the heat. Conversely, when you operate a 120V heating element at
240V, it burns up. ;-)
When you put 240 volts across the same resistance, you get twice the
current flow and 4 times the power. The water heats up 4 times as
fast, but uses the same total amount of energy. In actuality, the
total energy used by the spa is slightly less with 240, because the
pump will run about 1/4 as long circulating the water while the heater
is on, plus their is also a small savings in loss in the line along
I see no way you are
I have an older hot springs. It is 120v. It takes about 12 hours to get hot
in the summer, and about 20 to get hot in the winter. It seems to cost me
about 20 bucks a month during the winter to keep it up to temp. It is
outside on the deck, and I have to shovel snow off it to use it. I believe
that hot springs offered a 120v version, and a 220v version...I bought the
tub used, but before I did, I asked the same question of my friend, who owns
a pool/spa store. He said that 220 is more efficient, but my old tub
couldn't run the circulating/heating pump and the jets at the same time
regardless of how it was wired, and that going 220 would save me maybe 5
bucks a month on the heating cost, if that. So there's my 2 cents. I've had
it out there for about 5 years now, and never had a problem. It does cool
off pretty quickly in the dead of winter, but by that time I am usually
ready to get out anyway.
No. For heating 120 and 240 are the same efficiency. It may well be
that 240 will be more effective, in that it will heat faster, but it will
consume the same total amount of watt hours which is what you are billed
Now if you don't keep you tub hot, and you heat it up only to use it,
then the faster it heats up means you will have fewer loses as it heats and
that will cost you a little less. There is also that very low line loss as
Resistance electric heating is always 100% efficient. There is no way to
change it. It is a law of physics.
The only thing you would have saved is the difference in line loss,
which should be insignificant.
At 240V, the unit would be a lot more usable, so you might spend more
because you use it more. OTOH, you might could let it idle at a much
lower temperature with 240V because you can bring it up to heat so much
faster. However these 2 issues play out should be much more significant
than the line loss.
A 220 will cost a little less in electricity. Since a 220 pump motor will
have to run for 1/4 the time, it will save you maintenence costs for pumps,
too. My spas both have two pumps, so you can multiply that out. I used to
have a 110 spa, and it seemed like it was working all the time. These 220s
run a lot less.
firstname.lastname@example.org (Chris Lewis) wrote in message
That's not what we're talking about here. The spa pump has to run to
circulate the water whenever the heater comes on. If he wires the spa
for 240V, the heater element remains the same, so the spa will heat up
4 times as fast. That means the pump will run for 1/4 the time, which
is where the energy savings comes from.
So you're suggesting he runs 240V to a 120V heating element?
How long do you expect that to operate before failing?
Or are you assuming that if he had gotten the "240V option", the
heater would have been 4 times the wattage? It might not have been.
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.
When I bought a Hot Springs spa in 1989 one of its features is that
needed no special wiring other than a dedicated 120 volt, 20 amp
circuit. Either the jet pump or the heater with its small circulating
pump run at any one time -- not both together. Typically it takes 24
hours to warm fresh tap water (about 70 degrees F) to spa temperature.
Slow by 240 volt spa standards, but no 240 volt circuit necessary.
Use at least a 12 gauge wire, 10 gauge is better in the long run but
it is harder with work with and has a little more initial cost. The
higher voltage 220, when used on any wire, will have cooler wires than
running 110v. So, more energy will be lost to heat using the lower
voltage. A 220v circuit will require special plug and outlet, a
little more cost than a 110v outlet/plug. Personally, I'd go with the
220v, but I'm not sure how long it will take to recoup the cost.
I have a similar question. I am considering exchanging my tub for a
hot tub, but a small one, the same size as the standard tub or just a
few inches wider.
Why would I need a heater? It's indoors, and hot water comes out of
the tap. If it cools off too much while I'm in it (I don't plan on
staying until I shrivel up), I can add more hot water. Doesn't the
water heater make hot water more efficiently than the heater option? I
figured I could save some money by not even installing a heater. Big
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