Ok, first off I need to explain my project first. I have a wood pellet stove that I want to use to heat hot water for a radiant heating system. I will have to do a custom job because nobody makes a kit for my particular stove. My question is howong of a colper tube is needed to heat the well water from 55 deg f to about 180degrees f? Il probably be using .5in copper tubing. The surface temp of the top of the burn chamber, where I wou l d like to run the pipe, has a temp range of 250 to 450 deg f. Some kits have the copper tubing directly into the burn chamber. My particular model will not allow me to do this....so capturing the radiant heat is my only option. Are there other variables that im missing?