[Greenbuilding] Hot tubs and recirculating pumps

[Kevin Dalley]

Yet another hot tub question.  I'm confused about buying an energy
efficient model.  I know, hot tubs use lots of power, no matter what.
I may add more solar panels to offset the additional usage.  But the
hot tub isn't for fun, it's for health reasons.  Really.

Does anyone have reliable information about energy efficiency of the
tubs?

I include some of my calculations below, but my confidence isn't that
high.

The California Energy Commission established standards for hot tubs.
These standards were supposed to take effect January 1, 2006.  The hot
tub industry complained that the standards were not quite correct.
The standards correct for volume and surface area of the tubs.  This
is reasonable, but the standards don't include a minimum constant.  A
tub needs a certain amount of energy, regardless of size.  The energy
should increase in a way related to volume and surface area after
that.  Volume for heating, surface area for cooling.

In short, the standard still are not in effect, and I want to buy a
tub.

Many manufacturers use an 85W circulating pump which runs 24
hours/day.  This pump filters; much of the heat produced by the pump
is recovered and used to heat the water.

The Marquis tub, by contrast, uses a higher powered pump for
filtering, the same pump used by the jets.  It uses 3.2A at 230V. The
official recommendation uses this pump for about 6.5 hours a day, for
filtering, testing the heat, heating the water.

Probably, I can cut this back to 3-4 hours a day or so.  This is still
2.2-3kWh/day.

I can keep the heat off except for a short while before I use the tub.
With insulation, the temperature will be close to correct, and just
need a small amount of heating.  I can cut the filtering down from 2
hours twice a day to 4 hours a day, plus one hour after use.

The 85W pump *might* be better, but I don't quite have enough details
to decide.