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Author Topic: Solutions for heat bleedoff  (Read 4981 times)

greasemonkoid

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Solutions for heat bleedoff
« on: June 16, 2018, 11:46:26 PM »

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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shepherd boy

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Re: Solutions for heat bleedoff
« Reply #1 on: June 17, 2018, 04:12:18 AM »

 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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RSI

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Re: Solutions for heat bleedoff
« Reply #2 on: June 17, 2018, 09:08:14 AM »

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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greasemonkoid

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Re: Solutions for heat bleedoff
« Reply #3 on: June 17, 2018, 12:09:28 PM »

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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RSI

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Re: Solutions for heat bleedoff
« Reply #4 on: June 17, 2018, 12:20:32 PM »

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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greasemonkoid

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Re: Solutions for heat bleedoff
« Reply #5 on: June 17, 2018, 12:42:45 PM »


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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RSI

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Re: Solutions for heat bleedoff
« Reply #6 on: June 17, 2018, 02:04:36 PM »

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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greasemonkoid

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Re: Solutions for heat bleedoff
« Reply #7 on: June 17, 2018, 04:42:16 PM »

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.  :)


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mlappin

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Re: Solutions for heat bleedoff
« Reply #8 on: June 17, 2018, 07:57:09 PM »

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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E Yoder

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Re: Solutions for heat bleedoff
« Reply #9 on: June 18, 2018, 05:27:33 AM »

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?
« Last Edit: June 18, 2018, 06:48:58 AM by E Yoder »
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mlappin

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Re: Solutions for heat bleedoff
« Reply #10 on: June 18, 2018, 07:06:31 AM »

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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E Yoder

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Re: Solutions for heat bleedoff
« Reply #11 on: June 18, 2018, 09:16:25 AM »

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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greasemonkoid

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Re: Solutions for heat bleedoff
« Reply #12 on: June 18, 2018, 05:14:34 PM »

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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E Yoder

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Re: Solutions for heat bleedoff
« Reply #13 on: June 18, 2018, 08:12:04 PM »

I wouldn't run over 170 in the summer. Especially with a tall stack.
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shepherd boy

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Re: Solutions for heat bleedoff
« Reply #14 on: June 19, 2018, 02:07:45 AM »

 Mild steel unit may need to run hotter than 170 to keep condensation out. RSI should be familiar with this.
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