# 220 vs. 110 for Hot Tub

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• posted on September 19, 2004, 6:54 pm

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.
Cheers, Wayne
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• posted on September 19, 2004, 7:53 pm
Wayne Whitney wrote:

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.
--
Joseph E. Meehan

26 + 6 = 1 It's Irish Math
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• posted on September 19, 2004, 7:00 pm
Joseph Meehan wrote:

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. ;-)
Bob
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• posted on September 21, 2004, 6:16 am

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 the way.
I see no way you are

The resistance
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• posted on September 19, 2004, 1:42 pm
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.

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• posted on September 19, 2004, 2:32 pm
mark wrote:

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 for.
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 well.
Resistance electric heating is always 100% efficient. There is no way to change it. It is a law of physics.

--
Joseph E. Meehan

26 + 6 = 1 It's Irish Math
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• posted on September 19, 2004, 5:03 pm
That makes perfect sense. So you're saying that if I had gone the 220v route, I wouldn't have saved anything electricity-wise? It would just be faster, and with less line loss?

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• posted on September 19, 2004, 5:42 pm
mark wrote:

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.
Bob
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• posted on September 21, 2004, 6:21 am

Actually, at 120V, the spa will use more energy because the pump has to run in circulating mode while the heater is on raising the water temp. The pump should be on roughly 4 times as long.
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• posted on September 21, 2004, 3:05 pm
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.
Steve
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• posted on September 21, 2004, 4:20 pm

Cough.
A 1HP 220 pump motor will run exactly the same amount of time as a 1HP 110V pump, and consume almost _exactly_ the same power if they're being switched under the same conditions.
Basic physics.

No, that difference was for some other reason. Ie: a much wimpier 110V motor. Or different switching conditions.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.
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• posted on September 22, 2004, 12:18 pm
snipped-for-privacy@nortelnetworks.com (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.

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• posted on September 24, 2004, 1:40 pm

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.
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• posted on September 24, 2004, 1:55 pm

This is a 240v heating element, it just runs at 1/4 power on 120. The motor is tap selected for 120 or 240 with a configuration plug
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• posted on September 20, 2004, 2:18 am
mark wrote:

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.
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• posted on September 19, 2004, 10:43 pm
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.

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• posted on September 21, 2004, 6:23 am
wrote:

12/10 gauge for 40-50 amp 240Volts?
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• posted on September 21, 2004, 4:58 am

110 won't run the pump and heater at the same time, and it will take four times as long to get hot. You will not like 110 wiring to a spa.
Jeff
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• posted on September 21, 2004, 12:45 pm
wrote:

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 mistake?