On May 23, 5:05*pm, jamesgang wrote:
On Wednesday, May 22, 2013 9:46:55 PM UTC-4, wrote:
I'm thinking of installing a heat pump for my 15x30 pool. I'm told that the correct unit for my needs (an Aquacal TropiCal) puts out 112,000 BTUs (40 amps/5.8 KW). I'm thinking that a larger unit that puts out 141,000 BTUs (50 amps/6.4KW), would heat the pool quicker and require less time on, thus use, in theory, less electricity - but it's about $500 more expensive than the small unit. We'll probably only use the pool on the weekends. Not sure how long it will take to break even on this with running it for only a couple days per week. Anybody have any thoughts or opinions about this? Is my thinking skewed? Is it worth the extra cost? Thanks!

1 btu raises 1 gal of water 1 deg so do the math.

The other piece necessary is that heating eqpt is rated in
BTU's per hour, so a heater with 100K BTU
output rating, should raise the temp of 100,000 gallons
of water one degree in one hour. I don't know how
heat pump units are rated, but with gas fired units, the
BTUs are typically the INPUT energy, so you have to
decrease that by the efficiency of the particular unit.
If a 100K unit is 80% efficient, then it's putting out 80K btus.

The big unknown is the rate of heat loss of the pool and
that is going to slow down the heat rise.