wood stove hot water coil

[machinemaker]

We found a wood cook stove that needed a few minor repairs while scrounging at a local scrap yard. I formed a new hot water coil for the stove, but have not plumbed it up yet. By the way, the stove heats our old farmhouse very well. Disclaimer: where we live even the federal renewable energy department says we are so overcast that we would have to downrate solar panels to 30%, so solar has not been much of an option. However, with our wet summers, our hardwood forests grow like weeds. I want to wire a hot water circulation pump to this heating coil, and some snap disk temperature sensors to both the exit of the stove’s heating coil and our domestic water heater. The plan is if the stove's water is above 120 f the pump turns on and sends water to the propane water heater and back. If the water heater gets too hot {160 f ?} a solenoid valve shuts the flow to the water heater and opens a valve to hot water baseboard heaters in my shop as a waste heat dump.
Any thoughts, temperature suggestions, or ideas?

[joestue]

The best temp sensor we did for this was a 6" long tungsten rod inside a stainless steel tube. a lever with about a 10:1 ratio and spring loaded, puts the tungsten rod under compression. a screw in the lever with a hole drilled into the screw, seats the rod in the screw so it can't escape.

A standard snap action switch is then pressed against the lever.

as the stainless heats up the tungsten rod shrinks in length relative to the stainless and the lever amplifies that motion. the screw in the lever is what makes it adjustable. originally there was a ceramic element to provide zero thermal expansion in this device..
we put that temp sensor in the smoke stack.


so anyhow.. use a 20$ "solar" water pump off ebay. on battery backup....

we had an open system and dropped ammonia into the pipe to keep the ph low.


the pipes will creosote up every 2 weeks, so we drained the water out and fired the stove and burned off the creosote.

photo here in my comments:
https://www.reddit.com/r/heatpumps/comments/1fpzume/should_i_rip_out_force_hot_water_baseboard/

[Adriaan Kragten]

I am not sure that I have understood your problem. You have a wood stove in which you burn wood to heat water or do you use solar panels to heat water or both together? What is the function of the coil you are talking about?  I assume you want to prevent that the water becomes too hot.

The same problem you have in a car. Above a certain temperature, a valve opens and guids the water to the radiator. Can't you use the same kind of valve? However, in a car there is a pump which forces the water in the direction of the radiator. But such a system can also work without a pump because hot water want to rise but then the reservoir to which the water is guided by the valve must be positioned high.

[JW]

Ok    I am the last of the steam people. This topic benefits  3D cad drawing to models to 2d. Then post them on here.


JW

 

[JW]

  https://www.google.com/search?q=heat+exchanger+furnace.

 BUT make sure you use a non contact temp sensor. they give the best readings.

[joestue]

  https://www.google.com/search?q=heat+exchanger+furnace.

 BUT make sure you use a non contact temp sensor. they give the best readings.

and the batteries die and your wood stove boiler fails to turn the pump on and the pipes explode.

before we had a temp sensor automatically turn the pump on... my mom forgot to turn the pump on one time, before loading all the trash in the wood stove and lit it on fire.

at the time we had a heat exchanger on top of the wood stove that held 11 gallons of water. it got hot, started boiling.. she then turns the pump on when the steam came out.

well the garden hoses and the bailing wire pipe clamps we used on the smooth pipes wasn't intended for boiling water, it was intended for 120F water. so when the pump turned on and 215F or so water started flowing and the pipes heat up... the garden hose slipped off the pipe.

and 11 gallons of boiling water filled up the dining room. tile.. no damage. lol.

[JW]

I think he is trying to avoid ash, not to clog the heat fins.

MAKE SURE YOU USE a pressure release valve AT 60PSI or less

JW

[joestue]

I think he is trying to avoid ash, not to clog the heat fins.

MAKE SURE YOU USE a pressure release valve AT 60PSI or less

JW

creosote will collect below 500F. at which point water is 500 psi.

this is the reason its so much easier to have a smoke to air heat exchanger, instead of smoke to water . you can just turn the fans off and let the creosote evaporate.

500F air, doesn't take much cfm to extract most of the heat of the wood and retain good effiency.


when my folks had our system working right, you could burn wet wood and condense half the water in the heat exchanger. in theory, you do it right.. you can burn wet wood and get out all the BTU's you would get out of dry wood..

just have to figure out how to scrape the creosote off the pipes collect it, then burn it for fuel later.

[machinemaker]

sorry to be away for so long. This is a fairly modern wood cook stove and the hot water coil is a 3/4" formed black pipe that is separated from the firebox and the oven. It should see a minimal amount of flue gas and I do not think that creosote will be an issue. It is separated from the firebox by a removable 12-gauge steel plate. I am more concerned that the water if this coil will be too, scalding hot for domestic hot water. and I am planning to use hot water baseboard heaters next door in my shop as a way to dump excess heat.
kent

[joestue]

sorry to be away for so long. This is a fairly modern wood cook stove and the hot water coil is a 3/4" formed black pipe that is separated from the firebox and the oven. It should see a minimal amount of flue gas and I do not think that creosote will be an issue. It is separated from the firebox by a removable 12-gauge steel plate. I am more concerned that the water if this coil will be too, scalding hot for domestic hot water. and I am planning to use hot water baseboard heaters next door in my shop as a way to dump excess heat.
kent

its not hard to dump the heat. you may just want to figure out a passive way to do it. can you get a thermal siphon going where the wood stove can't get the water hotter than boiling because the convection currents will push it fast enough through a passive radiator, in the room the wood stove is in? that way the excess heats the room and inspires less wood consumption....