wood stove heat coil & exchangergreenspun.com : LUSENET : Countryside : One Thread
I have a soapstone stove that radiates a tremendous amount of heat for long periods. I've read some of the previous threads involving heat coils but still need some guidance. I placed a test copper coil in the firebox and circulated water through the coil with a small pump back to a water pot. I was surprised how quickly it boiled.
My goal is to store a small amount of hot water to feed a heat exchanger placed in the air plenum of my forced air furnace. I must store the water at a level below the stove.
How can I safely store the water without overpressuring? I would like to use a tank seperate from my existing hot water tank. Can I do this with some sort of zero pressure tank, and how could I automatically refill such a tank? Do you think a 5 to 10 gallon tank would suffice since I'm just circulating the water to the exchanger?
Last, do you think and automobile type heater core placed directly against the back of the stove would be more efficient than using a coil? I would like to keep the heat coil/core on the exterior of the stove if possible.
-- John Sink (Eli_john_us@yahoo.com), November 16, 2001
hmmmmm,, let me see, you want this for added heat to another part of the house, ,not for drinking/cooking water?? Do NOT use auto parts for drinking,,, will kill ya,,lead solder (yes,,stil using it),, treated with chemicals, ect. Why are you putting the coil INSIDE the firebox? why not just wrap the coil around the stack? wouldnt heat as fast,, but wouldnt be in the way for overheat and melt,,I can melt copper in my woodburner. IN order for a heat exchanger to work without a fan, ,you will need ot pressurize it,, or use an electric fan. Aoto refill,,,, ow about a hose attachment, with a toilet bowl float valve?
-- stan (email@example.com), November 16, 2001.
Thanks Stan. I will use the existing blower in my furnace(over 1300 cfm) to push the air past the exchanger. Good idea on the water refill.
-- John Sink (firstname.lastname@example.org), November 16, 2001.
Hi John; Will you please keep posting what you are doing.I am interested in what you are doing and I am sure that there are many lurkers as well. I am assume that you will not be able to use thermosiphioning without the fear of creating a 'boiler' that might overpressure.Maybe a very small pump can circulate the hot water cheaply.If you live in a area that has low humidity maybe you could make a simple humidifier in the air handler and wick the water down a screen (or waterfall effect). I agree with the 'toiled valve' or stock water valve to control the evaporation (alittle concerned about flooding the carpet). Ourfarm
-- ourfarm (email@example.com), November 16, 2001.
Sorry about the typoes.
-- ourfarm (firstname.lastname@example.org), November 16, 2001.
John: You're wise to reconsider putting the coil inside the fire box, especially with copper coils since copper will anneal(soften) over time when exposed to high heat.
I don't blame you for wanting to store some of the heat and water is a wonderful storage medium but I have to wonder of its worthwhile if you're only gonna store 5-10 gallons unless you plan to run the heat exchanger coil in your plenum while the wood stove is running and the water will only be a buffer so you can more readily transfer the heat to another portion of the house. The way I got it figured is 10 gallons will only store about 1300 btus. If you wanna use the surplus heat personally I think you'd be better off figuring out how to use the wood stove to preheat domestic hot water. It would be more cost effective.
-- john (email@example.com), November 16, 2001.
I don't think the copper coils will be a problem as long as they are kept filled. Make sure you use the heavy duty tube type, not just the cheapest. Annealing will affect the copper, but as long as it isn't damaged by bending or banging with the wood chunks, not too much of a problem. You might want to put a drip pan under the stove in case of leaks, though, to be on the safe side. Now, as far as the storage of water, I would recommend at least a 55 gallon drum, pump the water from the woodstove through the drum continuously, and vent the drum, setting everything up so that the stove side is actually not pressurized, but continuously circulating. Then, put another coil in the furnace duct and circulate water through that only on demand. If you want to heat water in a hot water heater, close the loop from the stove by putting another coil in the drum which separates the drum water from the stove water. Then, the continuously circulating hot water in the stove side of the system would be sent through another heat exchanger mounted to your hot water heater. (check with the outdoor furnace people for one of these, or the parts list for making one.) 1. don't pressurize anything and depend on relief valves for safety. 2. you can always change the copper coil to steel pipe later if it leaks. 3. send me a note if you want any more of my advice, I hope this is understandable and helps. Dan
-- Dan (firstname.lastname@example.org), November 20, 2001.
I used a stainless steel sink hung near the ceiling for water storage.I come off rhe drain and converted to 1/2 copper which i wraped around the stove then up to the heat exchanger then back to the sink.Works by thermosyphon.Works great
-- barry (email@example.com), February 12, 2002.