Still in the thinking stages on this project, but I've got an idea of what I want. This is a diverter that will sit on top of the wood stove. It will allow smoke to go right up the chimney during startup and will allow the cleaner afterburn to circulate through a masonry mass with the turn of 2 dampers. I have no idea how to size the masonry mass but think I can capture a lot of heat this way. Does anyone have advice on using something like this ?
As smoke cools it will deposit creosote. Poor designs may cause this creosote to become a fire hazard.
We have a secondary combustion chamber directly above our woodstove. Inside of it, I have 50-foot of 3/4 inch copper tubing loops, where we circulate water through a thermal-bank, which is then circulated through our radiant flooring.
Yep, I'm aware that cold smoke is a problem. That's the whole reason for the design. I let the smoke go up the chimney, then when I have a clean burning fire I can divert the waste heat to the masonry mass.
Yup, build up a strong draft AND let most of the gases burn off. THEN when it is just coals, divert the heat through the masonry. NO SMOKE through the masonry.
I had a Magic Heat. Had to run the cleaner rod several times a day or it would be stuck tight with the buildup of creosote. Cooled the smoke and provided extra heat, right up until the chimney filled with creosote and the chimney fire nearly burned down the house. Before you install one, ask your home insurance agent what he thinks.
I run a fire 24/7 in the heat season. Running the fire damper open while the fire gets going is fine. But running your smoke through your thermal mass when it is just clean coals, is short lived. Soon, you must add more wood and go back to the straight pipe mode.
With wood heat, a lot of heat goes up the chimney. Get that heat, gives you cooler smoke and a bunch of tar.
I'm more interested in capturing heat for a delayed release through the masonry. I get plenty of heat off the stove while it's running. Thanks for the pic - I am aware of those devices.
Most modern-day woodstoves are 80% efficient. That means, 80% of the possible BTUs in the firewood are being released to the home.
If I wanted to heat thermal mass, I would be thinking about designing something that will extract some of the 80% as opposed to extracting some of the 20% that is going up the chimney. That 20% is important in maintaining a decent draft and keeping creosote production down.
Most current production (Post 1983) are not designed for any chimney draft fixture. My experience is run the stove "EXAXTLY" as it was designed to be run, or pay a very highly skilled person to build you a "TRUE" air tight stove. They all advertise that their stove is an Air Tight stove.......but it is "NOT".
My stove is EPA approved - 5 years old. Once you're down to coals I don't think it matters how your stove is designed.
When I'm getting ready to turn in for the night the stove is glowing coals, no flame visible. I turn the intake air off and go to bed. At this point the surface of the plate steel stove is 500f and I have to believe that 500f is also going up the chimney. I also believe that in this situation, there is no more creosote in the exhaust to deposit anywhere. If the exhaust is diverted to a rocket mass type heat sink then back to the hot chimney, I will have adequate draft to start and maintain the flow. The unknown variable is how much masonry will be ideal to soak up heat. I have enough room in the stove room to build a bench type mass like the rocket mass designs, maybe 10 feet long so it would be a 20 foot loop. The materials are cheap enough to build it - I'm going to see how it works and I will report back. Thanks for the comments.
As those coals burn down, the draft becomes weaker. The draft will be even weaker if the flue gases are routed through thermal mass. You may wake up to a home full of smoke and/or carbon monoxide.
Heat your thermal mass with heat from the firebox, not from the flue.
My neighbor has a barrel stove. He built a thermal mass around the barrel with bricks. He burns a hot fire before bed and the thermal mass heats up. It radiates heat all night long even though the fire goes out after a few hours. The quick, hot fire produces little creosote. He builds one or two fires during the day depending on how cold it is outside.
The only downside I see is the need to start 2 or 3 fires each day. I light off my stove in October and let the fire go out in April.
The closest thing to mass heat absorption and dispersion from a wood heater I have seen was when we moved from a rented house that we had to buy a wood king brand wood heater of our own into a inexpensive 12 foot wide mobile home and were concerned about using wood heat in the mobile home due to the fire risks and spread speed associated with mobile home fires.
To eliminate the fire risk, we built a cinder block 5 foot tall 7 by 7 foot well house type building and filled the blocks with red field clay and insulated the tin roof and door to house the heater about 15 feet from the mobile home.
To feed the heat into the mobile home , we ran duct to the central duct of the mobile home.
That heat mass containment bunker worked so well that as soon as we figured out that although the heater only had to have fuel added two or three times a day, it allowed enough heat into the mobile home ductwork to almost make air popped popcorn, we added a venting fan to the stove bunker in addition to the static air inflow vents to vent off excess heat when needed.
Almost 20 years after selling that home and timber acreage when we moved here, the current owner still uses the outside heat bunker and has replaced the small heater only once that I have heard of.
I would look at doing it with a single valve. Instead of turning it could drop down in front of the bypass to divert exhaust up the chimney or raise to divert through the masonry. With 2 valves one could easily have a 'duh' moment and close both of them.
A wood gas generator heats the smoke up but limits the oxygen so it can't burn completely. The result is CO, methane, hydrogen, some tar, and nitrogen. This gas is flammable. When the wood gas is burned it produces CO2 and water.
A Russian mass heater burns the wood and smoke completely. It has unlimited oxygen for combustion so there is no creosote, just CO2 and water. You don't have to worry about the temperature of the exhaust.
A Russian mass heater burns the wood and smoke completely. It has unlimited oxygen for combustion so there is no creosote, just CO2 and water. You don't have to worry about the temperature of the exhaust.
Look at old tech, potbelly and cylinder stoves. They will crank out max BTU with marginal fuel. It is very simple,supply bottom air then add upper air supply when hot. Smoke burns. Air tight stoves are the biggest potential failure due to operator error.
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