Pool heater options on our crazy home made pools

Despite 90 degree temperatures outside, out pool just isn't warm enough to enjoy. Its in a shady area and is darn cold.

It is basically two "hot tubs", homemade out of concrete block and PVC pipe. When we bought the house, we decided they were worth trying to get running. With the help of a great friend and pool guy, they are up and running with a few issues to still work on.

So we really don't want to invest much into these pools that may not last.

Heaters: what's cheap? Redneck pool heater is amazing. What about a regular water heater?? Backflow preventer on one end and a pump on the other.

Thoughts?

As a former plumber -- held a master's license for 30 years -- I can assure you that you do NOT want to hook up an electric water heater.

The ONLY cheap heat for pool is solar. The black plastic panels can add 5 - 10 degrees to your pool.

Solar would be the cheapest after setup of course, and quite noticable for increasing your pool temp.. I noticed more benefit from my solar heating though in the spring versus the fall.. fall was when I wanted it more of course.. seems the overnight temps zap more heat out of the pool and you are lucky to recover it during the day so it's hard to keep up for long.. in the spring the nights keep getting warmer and you lose less so the solar really helps with an early opening.

I have always wanted to come up with some kind of wood heat for the pool... I can get plenty of firewood for little more than my efforts.. it's my main source of home heat during the middle of winter..