epetrevich@relavis.com wrote :
> This is a much cheaper way to operate a hot tub. Keeping about
> 250 gals of water at temp is much cheaper then getting it back up there
> over and over again. With a cheap unit, you need to run the jet for a
> while before you want to use it (sometimes it may be close to an hour)
Inch :
You've been listening to too many hot tub salesmen ! A little reflection on
the laws of thermodynamics should show that it _has_ to be cheaper to heat
the tub up when you want to use it : The heat lost from the tub is
proportional to the temperature difference between it and the surrounding
air. As soon as the water cools at all, that difference is lower, so the
heat lost is lower. Less heat lost means less heat to replace to bring it
back up to temp.
The problem with heating an electric tub when you want to use it is how long
it takes. Using your example of 250 gallons, that's roughly 950 liters, so
it takes roughly 14000 kilocalories to raise it from 25C to 40C (77F to
104F). If your heating element draws 50 amps at 220v, or 11 kilowatts, it
would take it roughly an hour and a half to heat the tub up. OTOH, my
150,000 BTU/hr heater would do it in about 20 minutes.
Randall
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