so i thought about laying out a conderser coil, building a frame with a glass opening and painting everything black. then using a submergible water pump to circulate water through it to heat the hot tub. i calculated i have about 400 feet of copper in this coil.

my biggest concern is the brazing material and how it will leach into the water.

any inputs? will it be a toxic bath or are the levels so low that it will not matter?

thanks

Art