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!