Outdoor Wood Furnace Info
All-Purpose OWF Discussions => General Outdoor Furnace Discussion => Topic started by: greasemonkoid on June 16, 2018, 11:46:26 PM
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I don't understand how you guys are getting by without boiling over in the summer. I was very meticulous at sealing the firebox and ash door with silicone and still had to bleed some heat off with a pair of 100 cfm fans across a heat exchanger in the shop. The first idea I had was to trigger the main hx fan with a temp controller, but the garage gets HOT, and very quickly when closed up. If left on I'd say the heat would build up to 140+ on a hot day? - just an educated guess.
So with the two small fans there is enough bleedoff to prevent overshoot under normal conditions with any type of wood. I'm content with the design, the shop doesn't get over 110 like this. Tonight the shortcomings were apparent. After a reload I checked the ash drawer and closed it back up. The lip that seats in the drawer seal wasn't seated completely, offset just a little. This created a considerable air leak. About 30 minutes later the over temp alarm sounds - fortunately I'm at home. Flue temps were 450 (they're usually 150-250 during idle).
I'm just brainstorming here, hopefully someone might throw in a slick idea I'm not thinking of. Perhaps there is a simple answer for a second stage of heat bleedoff. A small, 10 plate water/water exchanger crossed my mind, but then pumps, and a tank would be required. A small heat exchanger in the window is an idea I guess, but it has a pile of implications as well. How about an electric valve that opens and dumps some water outside after passing through the main DHW hx? Don't those get stuck?
I'm just a rookie boiler operator, not sure what everyone else does, but would like some more aggressive way to pull heat out that is automated.
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Fire can't burn unless it gets air. Been burning year round for over 20 yrs. Current stove, C375 had a stuck solenoid once and got a little warm once, but its doing great now. Don't have any fancy controls or even a shed, just sits out there like it came and gets a little wood every now and then. Making hot water and drying clothes.
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After you latch the ash pan, do you give it a kick? If not, try that. It will seal much better than just shoving it in and latching it.
How deep is your coal bed? In warmer weather you don't want to let it get too deep.
Do you have a coal model stove? If so, you need to seal around the grate linkage when burning wood. Also, burning wood in a coal model you should cover the back half of the grates with a steel plate.
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Great info, yes it is a coal unit. I had no idea on the grate cover. For better combustion air distribution I assume? Would small holes toward the rear increasing in numbers toward the front side be a good idea? I've got some .250" plate left.
Didn't even think about the leakage around the linkage :bash:
I don't keep much of an ash bed at all, probably because most of it falls through the grate, and there are fire brick in the bottom on both sides of the grate that holds what little bed there is.
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You mostly just want to keep air from going straight up the chimney.
The older wood model stoves had the grate all the way to the back and it would burn the bottom the of chimney pipe off and lose a lot more heat out the chimney.
The put a solid floor in the back half to fix that problem.
If it is possible, I would remove the back shaker grates. I never looked at them that close to see how hard that would be. The guy from Nature's Comfort told me it works ok to just lay it on top.
1/4" plate should work fine. You could experiment with holes but I think you want the air to mostly come from the front of the firebox
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The older wood model stoves had the grate all the way to the back and it would burn the bottom the of chimney pipe off and lose a lot more heat out the chimney.
That's a nice thought. Hope nothing got damaged... :o
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They didn't have the water jacket around the chimney then. It shouldn't hurt your stove, just lower efficiency and more likely to overheat.
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Gotcha.
Sealed off the grate lever slot and added the plate. Hope something good comes of it. I sweated off a gallon of water doing that job.
Thanks for the help. :)
(https://i.imgur.com/vrttdHtl.jpg)
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You could try lowering your set point as well, I wouldn’t lower it too much given its a mild steel stove but you could try 10-20 degrees and see if that helps.
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I don't understand how you guys are getting by without boiling over in the summer. I was very meticulous at sealing the firebox and ash door with silicone and still had to bleed some heat off with a pair of 100 cfm fans across a heat exchanger in the shop. The first idea I had was to trigger the main hx fan with a temp controller, but the garage gets HOT, and very quickly when closed up. If left on I'd say the heat would build up to 140+ on a hot day? - just an educated guess.
So with the two small fans there is enough bleedoff to prevent overshoot under normal conditions with any type of wood. I'm content with the design, the shop doesn't get over 110 like this. Tonight the shortcomings were apparent. After a reload I checked the ash drawer and closed it back up. The lip that seats in the drawer seal wasn't seated completely, offset just a little. This created a considerable air leak.
You guys have it figured out I think, there's got to be air leakage. Ashpan and firebox doors need to pinch down tight. Enough to compress the gasket. Check fan/ solenoid for leakage. The extended chimney creates more of a vacuum, probably a 1/4" hole could cause boiling. Wonder if teeing the chimney right above the stove could break the vacuum?
Should never creep over 10°, no matter what the heat load or outside temps.
I'm assuming there is a pump running at all times to stir the tank?
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Soon as it shuts off, a swisher sweet or something smokey makes a great way to check for air leaks. Just move it around the door, ash pan, shaker grate handle etc and look for it to suck the smoke in.
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Another method I've used is to shut the draft off right in the middle of a real hard burn. Then wait a minute or two for the firebox to pack full of smoke all the way down into the ash pan, then cap the chimney with a board and turn the draft back on, it'll puff smoke out of any crack even in the ash pan.
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That's a good idea ^. Yes there is a circulator pump running constantly. I also dropped the Ranco T-stat down a hair to 182. It overshoots by 3 degrees, but I've also got the fans that turn on at 185 and that pulls it back down a degree, then it slowly cools off and is stable.
A couple of spare squirrel cage combustion fans came in last week, it looks as if there could be a bit of leakage in the sheet metal housing also. I'll get up there and smoke it later this week and see what happens, in fact, right now the datalogger would probably reveal some good info. I'll post that up after a 24 hour log.
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I wouldn't run over 170 in the summer. Especially with a tall stack.
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Mild steel unit may need to run hotter than 170 to keep condensation out. RSI should be familiar with this.
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170 or a little lower should be fine. If it starts building up more creosote than usual then I would go back up it temp.
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All depends on pump size and delta T when talking temp. Depending on HX size and piping layout, DHW call may be a huge load. Condensation doesn't start occurring until ~132 degree return temps, so if there is good mixing in the stove and a proper piping system, you should be able to run down to 165 with a 10 degree diff or 160 with a 5 degree diff- possibly even lower if creosote doesn't become a problem. Even in the -40F dead of winter I still run a 165 supply with 10 degree diff, and a full load of heating and DHW hangs about a 17 degree delta T. Personally I don't understand the idea of burning year round and needing to have a heat dump when the wear and tear on my shoes walking to the stove twice a day costs more than heating DHW with LP, but that's just me and my small DHW load. Last time I filled my 500 gallon LP tank was in April 2015 and it's down to about 15% right now- a 3 person household has cost me ~$10/mo to heat water as well as the house during shoulder seasons, I can't afford to light a fire for that
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I've burned 10 summers with no heat dump with no overheating issues that I can remember. Various models. Running either 170 (conventional) or 175-180 (gasser) on the high end. But they've gotta shut down tight.
I like playing with a fire anyway, but now with 4 children it's definitely worth burning year round. But not everyone is in my situation. We roll through hot water, a flat plate is a wonderful thing.
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There is creosote running down the inside of the door, all inside really. Every few days I turn the water on and do a long burn. Depending on what the power bill looks like I may shut it down, but it sure is nice to have the water hot for a change. With 3 females in the house at 45 minutes a pop in the shower I would expect to see something change. Reminding myself I don't have to hurry in shower is a change of pace...
Nothing spectacular here, looks like someone was running the washer, shower or somehting a 10am this morning. The DHW circ pump doesn't seem to show up on the graph, it is set to 155*. The T-stat is set at 180 with a 10 degree diff, I think the logger reads 2* high.
(https://i.imgur.com/UigxtdKh.jpg)
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Ok, yes, I'm a paranoid geek.
(https://i.imgur.com/EyIx5qyl.jpg)
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What is it in the picture?
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What is it in the picture?
Lol, has me scratching my head too.
There is an Asco solenoid valve that looks like it goes to a tee with a sensor in the end and a pipe going out through the wall. I am guessing it is a bare pipe buried in the ground back to the boiler to bleed heat into the ground.
I wonder how close my guess is. ;D
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Neat idea. ^
That line is tee'd off of a hot water line after it passes through the DHW heat exchanger. Hot water squirts out the side of the house when overheat occurs, it is very aggressive and effective at pulling heat out of the boiler.
The sensor is part of the Control by Web. Sensors are cheap, figured why not.
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Yup, that would work. Cold well water would put a good load on like you said. :)