I wouldn't have a pool without a heater.

I like my water at a minimum of 85 degrees

. I have no insulation, but I do use a solar cover religiously and that really helps to retain the heat. The heater isn't used much in July, early aug. Once the kids were in school all day, we started turning it off after Labor Day, very rare september swimming, and it didn't make financial sense to keep heating it on the
off chance
one weekend
might be warm enough. The first summer with the pool we kept it open and heated into October. We were swimming October 2, since the air temp reached 85. 3 weeks later we got a $400 gas bill. That was the last time we did that!
I opened mid April. A week later they were forecasting mid 80s for the weekend, so on that Thursday pm I turned on the heater, and the temps went from upper 50s to low 80s. Of course the weathermen were wrong and the weather didn't cooperate, cloudy and low 70s temps, I wasted all that gas for nothing as no one wanted to swim. I was afraid to see the gas bill - not too bad it was only $80. I expected much worse!
Anyways, I love my heater.... I know folk round here who use theirs with no solar cover. Can't imagine what their gas bills are....
You definitely extend your swimming season with a heater. My BIL used to have a pool with no heater, and they were always swimming at his sister's house because her pool was heated.
Maybe you could talk him into a solar unit?
