is 220 cheaper than 115

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Natfuelbilll said:
the demand per phase on a 1kW heater at 120V is exactly the twice the demand per phase on a 1kW heater at 240V
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Sorry, no.

Look at your statement again. What is the size of the load at 120V? 1kW
What is the size of the load at 240V? 1kW

Demand is measured in kVA, not Amps. KW = KW, and in this case kVA = kVA.
 
LarryFine said:
That, of course, presumes that both the heater and motor(s) are dual-voltage units, and each's can be connected for full power at both voltages.

We know the motor would have to be dual-voltage rated, but some spa heaters use a single element wich runs, say, at 6KW at 240v, but only 1.5KW at 120v.

Usually, these convertible units can not heat while the pump motor is running on high speed, because the combined current exceeds a 20a circuit's capacity.
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You're probably right, but I was using a hypothetical to illustrate my point about equal loads at the two voltages using the same energy.

RHJohnson said:
Everything considered, the lower voltage must cost more to heat the water. I think we agree it would take longer to reach the same temperature, and at this same time the water is being cooled by the ambient. We ain't in no vacuum!
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Absolutely correct, in fact that adds to the probable increase in cost of running a 120V system. If it takes longer to heat up the same volume of water, you will be losing more heat into the ambient as it is trying to heat up. Remember, "R values" of insulation have to do with the movement of heat over time, so assuming the insulation is the same (again, hypothetically), then there will be more heat losses if it takes longer to raise the temperature.

The actual facts in the OP's scenario are as mentioned above unknown, so again, we don't know anything for sure about what that home show salesman was talking about. But IN THEORY, given all other things being equal, 120V will probably cost more to operate.

Wow... :roll:
 
charlie b said:
Higher voltage means lower current, and lower operating temperature. Take this notion too far, however, and the insulation system might fail, after which the motor will be very hot very briefly, and very cool forever thereafter.
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ultramegabob said:
thats pretty much how I understood it, but I just thought I would throw that out there, sometimes Im surprized what I find out:wink:
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For the context of this post, I'm not seeing this. Assumption: Motor feeder is sized correctly for the application.

Single phase, dual voltage 115/230V motor: wound with two sets of 115V coils, parallel connected for 115V, series connected for 230V - same current through each coil regardless if motor is connected 115V or 230V. Same current through each coil - same temperature.

What am I missing?

cf
 
Your not missing anything. I think we have all stated that any difference is a "Technical difference" when you do the math, or a very small difference due to the speed at which you can heat the water.......But the overall "noticable" difference is really zero. In addition to that it was all ready stated that there are too many variables for us to really come to any one single conclusion. Really this thread was about splitting hairs and debating all variables.
 
Here is an example of what you get at 120v:
Most Sundance spas must be connected to 240V electrical service, but some offer the option of operating on either 120V or 240V. While connecting to 120V can be less involved, most customers prefer the benefits of the 240V spa, which include quicker heating time and better temperature maintenance during cold weather use. This is because the heater output is four times as great in a 240V spa versus a 120V spa.

From another spa page:
120 volt spas have a 1.5 kW heater. They heat an average size spa approximately 1 1/2 to 2 degrees an hour! No you will not feel warm water coming out of the jets! 240 volt spas normally have a 6 kW heater. They heat 4 to 6 degrees per hour. I’ll let you do the math, but figure as a rule of thumb allow 24 hours to reach temperature with a 120 volt spa and 4 to 8 hours on initial heat up with a 240 volt spa.
 
active1 said:
Here is an example of what you get at 120v:
Most Sundance spas must be connected to 240V electrical service, but some offer the option of operating on either 120V or 240V. While connecting to 120V can be less involved, most customers prefer the benefits of the 240V spa, which include quicker heating time and better temperature maintenance during cold weather use. This is because the heater output is four times as great in a 240V spa versus a 120V spa.

From another spa page:
120 volt spas have a 1.5 kW heater. They heat an average size spa approximately 1 1/2 to 2 degrees an hour! No you will not feel warm water coming out of the jets! 240 volt spas normally have a 6 kW heater. They heat 4 to 6 degrees per hour. I?ll let you do the math, but figure as a rule of thumb allow 24 hours to reach temperature with a 120 volt spa and 4 to 8 hours on initial heat up with a 240 volt spa.
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Thanks. Looking at specs on dual voltage spas on the Sundance website, there is no difference in the HP rating of the pump motors at the 2 voltages, only the heater kW is different. Assuming that the pump MUST run along with the heater elements (as mine does), then if you have a 1.5 HP motor running 8 hours @ 240V, you end up with (roughly) 9kWH of motor use, and 120V for 24 hours, you end up using 27kWH. That looks like 300% motor energy use to me.
 
volts are one thing, but it really boils down to amps. the more amps you use, the more your electric bill will be. they say if you use more volts like 240 as opposed to 120, it will be more effecient, i think because the higher voltage balances out the the lower amps. when i installed lighting in commercial jobs like home depot, we used 480v because they said it was more effecient. i guess the higher the voltage = less amps you need or use.
 
scottytoohottie said:
volts are one thing, but it really boils down to amps. the more amps you use, the more your electric bill will be.
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Not true, I'm afraid. You pay for watts, not amps. Higher voltage may mean lower amps, but the difference in efficiency has more to do with the improvement in power losses. Less amps means less I2R losses in the wires. However, for small buildings, and for houses in particular, the difference may be very small.
 
So after reading all this is same to say if you have a spa wired 240-volt and one wired 120-volt the cost to heat the water is about the same?
 
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