220 vs. 110 for Hot Tub

[ed]

I have a hot tub that I'm getting set up and it can be wired with 110 or 220 volts. I want to weigh the options and need to understand the benefits of each option. At this point I know that wire and breaker for 110 will be quite a bit cheaper. The amperage rating at 110 is only 20amps and a single pole GFCI breaker and the thinner guage wire will be significantly cheaper than the double pole 50amp breaker and the heavier wire that I would need for the 220 option. This is about all I understand about the differences. I have this vague notion that the 220 will be cheaper for me in the long run but I'm not certain why. Could someone help broaden my understanding of the two? Thanks ahead of time, E

[I-zheet M'drurz]

Those numbers don't make sense for an "either" situation. if it was a choice, the watts would total to be the same in either case. 20A@110V would be 10A@220V, not 50A. Without being able to see it (or the manual/installation guide) I'm going to hazard an educated guess that you need *both*.

The 110V is likely feeding pumps and lights, the 220V will be for heating elements.

But hey, I could be wrong. ($1 Dennis Miller)

[toller]

Ah, maybe you have those amp requirements backwards?

120v requires twice the amperage as 240v. (or provides 1/4 the heat, depending on the wiring)

Of course, if you really need 110 or 220 you will have to invest in a transformer, and that will really jack up the prices.

[zxcvbob]

Hook it up to 220V (actually, it's more like 240V), because at 120V it's going to take forever to get hot. You can save a little by using aluminum SE cable. There's a lot of details to wiring it up safely and according to the wiring codes. And you need still need a GFCI.

No offense, but if you're asking basic questions, you really shouldn't tackle a job like this yourself. Hire an electricial, or do a lot of studying first.

Best regards, Bob

[Greg]

Buried somewhere in your users guide it is going to tell you that it takes 4 times as long to heat up the tub at 120v and that you can't run the pump and the heater at the same time. If you go the 240v route you can run the tub at it's full capacity. You will need a 240v 50a GFCI breaker but that will really be the most expensive part.

[Joseph Meehan]

I agree with I. You have something wrong. Those numbers are not right.

110 @ 20 amps is 2,200 Watts. 220 @ 50 amps is 11,000 amps. It can't be right.

I also agree that if you did not see this yourself, you need to hire a professional for this job.

[HA HA Budys Here]

Where's he going to find SE cable with a neutral and a ground? SE is service entrance and in the USA that is ALL it can be used for, services.

[HA HA Budys Here]

The 120v "option" is indeed a sales tactic. This way, the salesmen can say "Oh it plugs into any ordinary 20a circuit" and not be lying. When this option is employed, the tub will not run both pumps (if it has 2 pumps) simultaniously. It's one or the other. It also will not heat while a pump is on anthing other than it's lowest "maintainence/filter" setting. And like you said, it will take a lot longer and use signifigantly more power to heat.

[zxcvbob]

I don't know if he needs a neutral or not. (probably does) If so, he can use SE cable type "R", a.k.a. SER. My point was that aluminum wire is appropriate for high-amperage circuits like this.

Best regards, Bob

[Chet Hayes]

Bingo! That's absolutley correct. The heating element remains the same, so with 120V the power to the heating element is 1/4 what it would be with 240V. And however hot it gets before you turn the pump on, it's all down hill from there, cause with 20 amps, there isn't enough current to run the pump and the heater. Plus, if you want to keep it at a lower temp most of the time to save energy and only raise it to full temp prior to getting in, it will take so long at 120V as to be impractical.

Now why it's so hard to find these simple facts out, I don't know. I went through this 15 years ago when I bought a spa for inside my home. The best explanation of the difference I could get from the dealer what, 120V is fine for inside, 240V is only needed for outside, it heats a little slower. When I figured out the truth, before I even turned it on, I had to pay them to come out and switch the power pack in the unit so that I could go to 240V. Now this has me wondering, was it really necessary to switch it? Seems like it was, since I watched them and they did in fact switch it, so I may have had one where the packs were in fact different.

I would only go with 120V if running 240V was nearly impossible. Also, make sure you check code requirements for GFCI, accessable disconnect near the spa, and bonding of any metal near spa.

[Joseph Meehan]

Did you mean more time? Total power (watts x time) is the same.

[mark]

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.

[Joseph Meehan]

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.

[Chet Hayes]

He has it right. The majority of the amps are for the heater, which is the same unit whether 110 or 220. So the current drawn is twice as much at 220 and the heater generates 4 times as much power/heat. And the control unit won't allow the pump to run at the same time as the heater with 110, while with 220, it will, so this adds to the current needed at 220 too.

[mark]

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?

[zxcvbob]

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

[Joseph Meehan]

Hold on there a minute. I am not sure what you are saying, but it seems you are saying that it takes more total power, to heat a given amount of water the same temperature rise using 240V than using 120V. If so that is just not right. No way.

BTW where are you getting this 4 times thing? I have been letting it ride because of issues with heaters designed for 120 vs. 240, but that just is not so.

10 amps at 240 = 20 amps at 120. With resistance heat there is just no way you are going to make any serious change in that! I see no way you are getting this 4X thing. Maybe you should re-think that again or maybe we are just not communicating well at all.

[Wayne Whitney]

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

[zxcvbob]

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

[Joseph Meehan]

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.