Cheapest way to heat up a pool?

[inetdog]

My mother in law lives up north and it gets chilly. She is always complaining that thee can't use the pool like they want to. My wife and I were going to buy her and my father in law a pool heater but for that pool size, 12 x 24, it isn't going to be cheap. I was thinking if there was a solar option that would work as good but cheaper in total cost. Any ideas?

The best solar option is solar thermal panels combined with a variable speed pump which will save them on electricity.

You can DIY solar thermal panels for pool use, and there are some nice designs at homepower.com. We can give you some good advice here and answer questions but the wealth of simple designs in detail they have are better than you can get here.
Or you can go with commercial solar heating panels. Be sure to use the type that circulate the water through tubes in the panel rather than the kind that use vacuum insulated tubes with a manifold to transfer the heat to the water. The latter are more suited to Domestic Hot Water (higher temps) and winter use.

[SolarFox]

My mother in law lives up north and it gets chilly. She is always complaining that thee can't use the pool like they want to. My wife and I were going to buy her and my father in law a pool heater but for that pool size, 12 x 24, it isn't going to be cheap. I was thinking if there was a solar option that would work as good but cheaper in total cost. Any ideas?