best system that i have seen is one that use glass vacuum tubes, you can buy em as there designed for houses but only about 2 foot by 2 foot, or you can buy the vacuum tubes straight of the net and make your own system.
hotwater vacuum tubes etc
Alternatively the tubes themselves aren't hard to make, you just need a few flower vases or bottles that fit inside each other, some epoxy
and a vacuum pump.
*** youtube that one if you like
Anyway regarding the water
temp, these things will heat water in the shade, so you be the judge.
when i get around to it, they will be the system that i will install on the targa of my boat, and ill only use two tubes.