jeudi 25 juillet 2013

Heating a Spa (Gas or Electric)

Hello,

So, this is a science and mathematics question. We are thinking of installing a Spa (Hot Tub) and I'm trying to figure out if it cost less to heat with Gas or Electric. Here is my analysis. Could anyone check my figures, let me know if I'm anywhere near correct? TIA.



1 BTU can raise 1 lb. of water by 1 Degree F.

1 KWH = 3413 BTU

1 Gallon of water weighs 8.35 lbs.

Assume 450 gallon spa, or 3747.5 lbs. of water (8.35 * 450)

So, it would take 3747.5 BTU to raise 3747.5 lbs. of water by 1 Degree F.

I pay $.31 per KWH (I'm way over base line and pay the third tier rate)

So, it take 1.1KWH to raise 450 Gallons by 1 Degree F (3757/3413)

or $.34 worth of Electric power (.31 * 1.1)



1 Therm = 100,000 BTU

0.37 therms to raise 3757 lbs. of water by 1 Degree F (3757.5 / 100,000)

I pay $1.10 per therm (Over baseline on Gas too)

or $.047 worth of Natural Gas (.037 * 1.10)



I think more realistically, I should figure more like 20 Degree rise, from an idle temp to ready to use temp. This would cost $6.80 Elec or $.94 Gas.



I believe another advantage is that Gas heats much quicker than Electric.

Also, we live in Southern California, so freezing is not an issue.

It looks like it cost about twice as much to install gas, but if my analysis is correct, it should pay for itself after a couple of years.



Any comments would be appreciated.



-LF





via JREF Forum http://forums.randi.org/showthread.php?t=262778&goto=newpost

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