Ideal flue temperature

 
nickdearing88
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Post by nickdearing88 » Thu. Dec. 28, 2017 7:09 pm

I just got a magnetic stove thermometer so I can start keeping track of flue temperature. I'm trying to get an idea of the ideal "mix" and "max" temps on my furnace.

I'm sure every setup is different but what would be a good place to start with a hand-fed, natural draft furnace. It's rated at 100,000 BTUH, 6" flue exhaust, connected directly to a 6" SS liner within an interior masonry chimney, about 30' tall from inlet in basement to top of chimney. The stove pipe exits the furnace with a 45* elbow, goes up to the chimney about 2' at a 45* angle, then another 2' into chimney horizontally.

Where is the best place to put the magnetic thermometer on the flue pipe?

The minimum temp I'd like to find would be how much I can close the air supply while maintaining draft and burn. As for max temp, I understand there is a good max temp to prevent wasting excess heat up the chimney.

Would 200* - 400* be a logical starting point?


 
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Post by franco b » Thu. Dec. 28, 2017 7:17 pm

Ideal flue gas temp. should be high enough to prevent condensation in the chimney. That would be about 250 degrees inside the pipe. Surface temp. usually about 100 degrees cooler.

Having that interior chimney is very good. Easier drafting and gives off heat to the house rather than outside.

 
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Post by coaledsweat » Thu. Dec. 28, 2017 8:55 pm

There is no magic number. You need two of them, the one going up the chimney and the one coming out of the appliance. They will tell you the sweet spot.

I'm convinced there is no problem with condensation in a coal fired application. I'm not sure it is possible. I've never seen a whisp of water vapour from a coal fired chimney no matter how cold it has been.

 
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Post by rberq » Thu. Dec. 28, 2017 9:02 pm

nickdearing88 wrote:
Thu. Dec. 28, 2017 7:09 pm
Would 200* - 400* be a logical starting point?
"Logical" to me is, you adjust the furnace to provide the heat you want, and flue temperature is what it is.

A damper -- manual or barometric -- may help to control draft and likewise reduce heat loss, but don't choke it off so much you get exhaust escaping into the house, nor do you want to choke it to the point the fire doesn't burn well.

It sounds like what you really need is a manometer (and the draft specs for the furnace) so you can tell whether you have too much or not enough draft and use dampers appropriately.

 
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Post by oliver power » Fri. Dec. 29, 2017 7:06 am

A good starting point is; Stack temp with magnetic thermostat should be about 1/3rd the stove mass temp. Stove brands will vary.

 
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Post by hotblast1357 » Fri. Dec. 29, 2017 7:26 am

For maximum efficiency, just enough to establish the correct draft recommended by the manufacturer, anything more is just heat up the chimney.

 
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Post by franco b » Fri. Dec. 29, 2017 1:29 pm

Any fuel containing hydrogen will have water as a byproduct. coal, wood , and oil are all hydrocarbon fuels. Those old German long stem, porcelain bowl pipes had a hole in the bottom of the bowl to drain the water out.


 
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oliver power
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Post by oliver power » Sat. Dec. 30, 2017 10:07 pm

OK Franco; You got me! What's a German porcelain bowl pipe?

"Those old German long stem, porcelain bowl pipes had a hole in the bottom of the bowl to drain the water out".

 
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Post by franco b » Sun. Dec. 31, 2017 12:01 am

oliver power wrote:
Sat. Dec. 30, 2017 10:07 pm
OK Franco; You got me! What's a German porcelain bowl pipe?

"Those old German long stem, porcelain bowl pipes had a hole in the bottom of the bowl to drain the water out".
I should have included that they were, and are, tobacco pipes. Perfect examples of a bad firepot. Thin porcelain bowl which loses heat and needs constant puffing to stay lit. That makes a hot smoke so the long stem is to compensate for that. Both brier wood and meerschaum are good insulators, so keep the tobacco burning with minimal air just like a good coal burning insulated fire pot will.

 
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Post by VigIIPeaBurner » Sun. Dec. 31, 2017 12:30 am

coaledsweat wrote:
Thu. Dec. 28, 2017 8:55 pm
There is no magic number. You need two of them, the one going up the chimney and the one coming out of the appliance. They will tell you the sweet spot.

I'm convinced there is no problem with condensation in a coal fired application. I'm not sure it is possible. I've never seen a whisp of water vapour from a coal fired chimney no matter how cold it has been.
1/2 hr after reloading at -8*F. Coal is in a covered bin, buckets, mine run lump crushed at mine, not washed nor spritzed. Buckets brought inside at least a few hrs before loading. Must have had some water in it from someplace. I keep loaded 5 gal. buckets covered outside before pouring into 2 hods. I never saw it before or after.

Image
[/quote]

 
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Post by Lightning » Sun. Dec. 31, 2017 7:33 am

VigIIPeaBurner wrote:
Sun. Dec. 31, 2017 12:30 am
1/2 hr after reloading at -8*F. Coal is in a covered bin, buckets, mine run lump crushed at mine, not washed nor spritzed. Buckets brought inside at least a few hrs before loading. Must have had some water in it from someplace. I keep loaded 5 gal. buckets covered outside before pouring into 2 hods. I never saw it before or after.

Image

What? Yer burning volatiles, hydrocarbons (hydro lol ;) ) at a half hour in. Oh, my bad - that must be a gesture of sarcasm, I'm kinda dense on occasion :lol:

 
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Post by Turbogeno » Sun. Dec. 31, 2017 7:37 am

The way it's dissipating quickly sure makes it look like water vapor. I had the same white smoke the other day on a cold morning after reloading but it drifted slowly for close to 100' before you couldn't see it. Because of that I decided it was smoke. I've never seen anything from the stoker but I would like to see what happens on a cold morning with a high feed rate.

 
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Post by scalabro » Sun. Dec. 31, 2017 7:41 am

I’ve seen the white “smoke” right after reloading on both my old HMKII and all three of the Baseburners I’ve run.

 
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Post by hotblast1357 » Sun. Dec. 31, 2017 7:54 am

I see it on my boiler when it fires, after I fill the hopper, coal is dry. You can hear the fire making a weird noise after the combustion has shut off, almost like a boil.

Burning Lehigh.

We have 3 more hand fed stoves do the same thing when reloaded. Same coal.

 
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Post by scalabro » Sun. Dec. 31, 2017 8:17 am

Just now 5 minutes after reload.

OAT 4*F, humidity 73%, baro 30.21 rising, dew point -2*F

Blashack stove size left over from last winter in the 1891 PP Stewart baseburner....

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