On 10/5/2015 6:58 PM, Dean Hoffman wrote:

It would have to be a pretty small "load" to get by with just ~1800W
(for pump, blower and heater).

To add to Don's point, my drip coffee maker needs 900 watts or
7.5 amps.
I don't know what a water bed would need for power. That would
probably be a better comparison. The hitch in that comparison
would be an enclosed, blanket insulated bag of water vs. and open tank.

And, do you want to leave that tub *heated* 24/7 just so it is
"up to temperature" when you decided to use it? You can arrange
for the heat to be switched on before you are *likely* to want
to use it -- but, if it takes a long time to get up to temperature,
you risk heating water for a long time -- only to NOT use it.

[By contrast, a higher capacity heater will let you postpone
that decision until you're reasonably sure you want to use it]

In places with high cooling loads, you can purchase a heat exchanger
to harvest "waste heat" from your ACbrrr and redirect this to heat your
pool, hot tub, etc. Thermostatic controlled so you don't end up
feeling like a boiled lobster (if your cooling load is considerably
larger than your hot tub "heating load").

No idea as to installed cost but sure looks like a clever idea!