Let me start off by saying that I am not a contractor but a DIY homeowner/fabricator. I live in New England, needed an inexpensive way to heat my new living room so I built this heat exchanger for my wood stove last year to heat the radiant heat loop in my garage-turned living room. I couldn't find anything like this on the internet but used some information that I found on this site so figured I'd return the favor and put this out there for others to see.
The exchanger was soldered in place on the stove to make sure that it fit snug and is connected to the rest of the system in the basement via two unions. This way I can disconnect the whole system and move the wood stove if necessary. There is also a high point air vent at the top of the exchanger.
It's a big room (420 Sq/Ft) with 7" of concrete over the pex loop and a thick carpet and pad. I was nervous that this set up wouldn't be able to heat that much floor but it worked fantastic all winter long, keeping the room at 74 degrees.
Two relays control the whole system. There is a aquastat on the back of the stove that starts the circulator pump when the water directly around the stove is up to temp. The aquastat in the basement checks the overall temp of the heat loop. When that temp is at 120 degrees and the room calls for heat the relay open the 3-way directional valve which then loops the water to the floor until the water goes back down to 80 degrees at which point the loop closes and the cycle continues. There is a check valve just to the left of the "T" on the bottom pipe that stops the pump from pushing water back through the floor loop when the room is not calling for heat. The 3-way directional valves "off" state is set so that if I lose power the loop to the floor is always open. This should hopefully alleviate any over temp/over pressure issues when I lose power. There is also a pressure tank and release valve incase that happens. In the future I may upgrade to a back up battery for the circulator pump. When dealing with high temp water/steam one can never be too careful. The two on/off valves with drain allow me to isolate the heat exchanger, drain it and disconnect it without having to drain the entire system or make a mess of my floor when I do.
The reheat rate for the heat loop couldn't always keep up with the request for heat in the room so I would manually set the system to just loop the whole floor, then at times I had excess hot water available so I will be making a few upgrades/changes for the upcoming season. One will be to jacket the copper pipes with cement board under sheet metal to make it even more efficient. My plan is then to add a 3-4' length of radiant baseboard to the heat loop in the basement with some computer fans behind it. When the room is up to temp and I have excess hot water in the loop the fans will kick on to heat my basement. I'll update pics and info as I make them and hopefully it will not take me a year again. Overall I am very happy with the system and it cost me roughly $700 to build. I also did not notice any significant change in the amount of wood that I burned this year or a drastic change in my electric bill due to the circulator pump. Any questions or concerns feel free to comment.