Pool heaters.. Big subject in Florida; you might not think so, but remember, most Floridians are
very used to heat, and we freeze at 60 degrees. We don't use our pools between November and April even with pool heaters; no sane person goes in the water if it's less than 78 degrees, and the air temperature must be warmer than the water.
So. Our first pool had no screen enclosure, so we had no pool heater. A screen enclosure blocks about 30% of the sun. The water temperature was above 80 F from April to October. We moved, however, and our current pool has a screen enclosure. The only way my wife could tolerate it is if the water is heated. We still do not use the pool from November to April, but once things start to "cook", we maintain a pool water temperature of 85 F or so, often above 90 F. That's tolerable to a long-time Floridian. Even I get in the pool when it starts to approach 90.
SO, that's the reasoning. Now, for the method. I used to be a propane dispenser, so I had some price advantages when it came to propane appliances. I was able to find a used propane pool heater for $500. I got it hooked up at the same time as we had the solar water heater installed, so there was really no extra charge for installation. It's rarely turned on; just there for backup for those times when our insane Winter guests insist that they could really use the pool. For example, my wife's sister is from Walnut Creek near San Francisco; her BEST Summer conditions for swimming are not as good as our worst Winter conditions...(slight exxageration, but close). Anyway, we occasionally fire up the propane heater in the Winter, but never for ourselves.
The solar panels are black plastic tubes used for pool heaters but not for domestic water heaters. I once read a long article on the Web as to why that is so, it seemed valid, but I forget most of it. Suffice to say, the pool heater system is nowhere near as sophisticated or expensive. We have a 14' x 30' pool that runs to 6' deep; we have 7 panels on the roof. The flow is controlled by an electric valve with a thermostat and a control unit on the wall; set the temperature desired, and forget about it. When (or if, if the cooler weather) the temperatures are achieved, the valve rotates shut and the water goes back to normal circulation through the filter until the thermostat notices that the water has cooled down, then the valve opens and the water is circulated (by the same pump) up onto the roof, through the panels, and back. Pretty simple. If I recall, the total cost was less than $2,500 installed. The heater panels survived the hurricanes just fine; I had to have them removed before our new roof was installed, and re-installed after, but the insurance company paid for that as well as the roof.
It's a fairly simple do-it-yourself operation to install one. I didn't do my own because my business was still demanding most of my time back then; I can't do it now because of my health, but if I was 20% stronger I could do it easily.
A wading pool will be fairly easy, because it will be shallow enough to get some heat from the Sun, even in Winter, and the shallow depth will allow the cooler water to mix with the heated water better. However, in the Winter, you may not be able to raise the temperature enough to make a Floridian happy. The limitations are on the relative differences in temperature; the cooler it is, the harder it will be to achieve a decent warmth. Most of your guests will be used to colder water anyway, however, and kids seem to generate enough heat when at play that they'll heat the water themselves!
I did a Google search for "solar pool heating" and came up with some great hits, including
this one in which they claim to advise you how to build your own system for $100. It's a site for selling on-line books, and I have no idea of the quality or validity of the offering, but that gives you some idea what's out there.
