I purchased two Hilkoil steel loops, one small, one long, i have a huge wood stove. i was sure to measure very accurately and have them end up being mounted up against the fire brick horizontally across the back of the stove and along the right side up-against the fire brick.. of course both pipes in series. i have an 80 gallon ceramic lined water tank mounted in the closet directly behind the wood stove. copper pipe connects the input and output of the heating coils. we have a LOT of power outages in our neighborhood so i wanted to be sure that convection would supply the needed movement of water up to the top of the tank... thus avoiding possible explosions if i was relying on an electric circulating pump. really wanted to be sure that i could continue to use my wood stove to heat the house in case of power outage without blowing up pipes and tank! it has worked wonderfully. we have two young children, diapers, a soaker tub and constant dishes and laundry. A tempering valve is an absolute necessity. often, in the 80 gallon tank of heated water there will be 160 degree f water at the top and 140 fr water at the bottom. well water comes in at 42 degrees in winter. the whole system is tempered to only release 124 degrees water to the electric hot water tank which clearly doesn't come on. Electric bills have dropped from $480 a month to $110 a month. our home is all electric. An interesting note: while a raging fire with great wood and walls of flame does output 140 degree water... so does a bed of coals with zero flame... especially if you push the coals up agains the hilkoils. so you can make hot water in the spring and fall if your good at keeping a coal bed going. i have 5 temp/pressure relief valves along the entire circuit out of paranoia... i have never blown a valve yet in 3 years of usage. only drawback, my current system can make it tough to heat the house itself if it's below 10 degrees f outside... i'm sure the water is pulling a good bit of heat out of the firebox! Some important points: to encourage natural and reliable convection... start fires slowly or you can boil water in the coils if convection hasn't started moving in time. i've only allowed 23.5 degree angles on all my copper fittings aside from the ones that connect the two hilkoils in series. i have my 80 gallon tank 4 feet above the installed coils.. i'm sure the higher the better. Use copper, install several pressures/temperature relief valves in the system, definitely an expansion tank, absolutely need a tempering valve, put several input and output temperature meters (analog) in key places such as input and output of the coils and top and bottom and output of the storage tank... this is the only way you can obsess over and learn how to create the most hot water in the safest manner