A while ago I speculated wildly about the cost of heating a jacuzzi. Since then, I got hold of an hour meter and fitted it, so I now know exactly how long the element is on for.
Turned the jacuzzi on on Friday evening, with the water at 10 degrees. On Saturday evening the temperature was at 46 (! — I modified the thermostat a little and my setting was obviously off) with the hour meter reading 12.17 hours. Since the element is a 4kW unit, that’s 48.68 kWh, which costs around R50 these days.
My original calculations worked out to about 28 kWh, but it did not factor in heat loss — i.e.Â the energy to heat the water, not to keep it warm.
Well, the hour meter reports that the element was on for six hours from Saturday evening to Sunday afternoon (a period of 19 hours), keeping the water at 40 degrees and the cats happy (they discovered they can lie on the cover, their own hot-water bed). This work out(roughly) to 30 kWh (or R30) per day.
Bottom line: a jacuzzi loses a lot of heat to radiation, and it’s cheaper to turn it on as needed than to leave it on all the time.