Flue gas...what's too hot?

[got wood?]

one of my stoves is an older Lopi Endeavor (came with the house) that has a single wall flue feeding into a class A SS chimney. I've got a flue gas probe thermometer about 18" up the single wall pipe that ranges from 0 - 1700 degrees F. When I run the stove, I had aimed for roughly the mid range of the probe ~ 900-1000 degrees...sometimes when reloading it climbs to 1300 or so then settles back down. Recently I moved the magnetic stove-top thermometer from my other stove to this one and the stove was around 700 degrees...and just stayed there.

I was pretty shocked thinking that was pretty hot. Is that a usual temperature delta between stovetop and flue-gas? According to the Lopi site, 800 is considered overfiring, yet I've got primary air shut off when reloading and it still lights up to 1300. Time to replace gaskets probably. Anyone else monitor their stove with a flue-gas probe thermometer?

 

[begreen]

That sounds very hot to me. The hottest stove I owned was the old Jotul 602. Even with that stove the stack temps rarely got over 700. With the Castine, it rarely gets above 450. Sounds like you might want to consider a stack damper. That made all the difference for our 602.

 

[BrotherBart]

Yep. Sounds way to hot to me. I have been intending to start a thread on flue temps for a while now. UL1777 for stainless liners is only for contineous flue gas temps up 1,000 degrees. Makes one wonder what the contineous rating is for the snap together black pipe. We get concerned about how hot the plate steel is getting but don't seem too concerned about that snap together tin sticking out of the top of it.

 

[berlin]

1300 is pretty hot, you won't see that from the fire in the stove. it is likely that you are flaring off some small creosote/soot accumulation from time to time when reloading, this is not uncommon and is actually a good thing, better to burn it off periodically than all at once after a large accumulation.


"stainless liners is only for contineous flue gas temps up 1,000 degrees. Makes one wonder what the contineous rating is for the snap together black pipe"

a lot of that rating has to do with the lack of pipe's ability to insulate effectively at continuous temps above that temperiture. btw, mild steel can take more heat, and heat cycling than stainless of the 316/304 veriety. i've seen situations where stainless would melt, sag, crack, and burn through where mild steel wouldn't have. some grades and of course inconel is not what i'm talking about here.

 

[fespo]

My stove pipe runs hot too. It is always hot even with a stack damper. It runs up to 900 to 1000 with no problem on start-ups. Then down to around 600-800 range. I have probe thermometer about 18” up also. but my pipe is double wall. Once I shut down the air to about 90 to 95 % then it will come down slowly. Sometimes after the fire settles down and its been burning for about a 45mins or so the stack and stove top will be in same range. usually pipe/ flue gas is hotter. I do not know whats up. I burn all oak on cold days, warmer days a mixture of elm, oak, maple and what ever else is in the pile.

 

[got wood?]

Yep. Sounds way to hot to me. I have been intending to start a thread on flue temps for a while now. UL1777 for stainless liners is only for contineous flue gas temps up 1,000 degrees. Makes one wonder what the contineous rating is for the snap together black pipe. We get concerned about how hot the plate steel is getting but don't seem too concerned about that snap together tin sticking out of the top of it.

really?? 1000 for continuous burns is the max? I run mine just under that most of the day. I was planning on replacing the single wall inside the house with double lined...but leaving the class A chimney the way it is. Both my stoves are just the Class A 6" flue BTW. No damper

 

[carpniels]

That sounds very hot to me. The hottest stove I owned was the old Jotul 602. Even with that stove the stack temps rarely got over 700. With the Castine, it rarely gets above 450. Sounds like you might want to consider a stack damper. That made all the difference for our 602.

HI Begreen,

Those temp you are mentioning, are those temp in the stove pipe or with a magnetic thermometer on the top of the stove? Please elaborate, because that might have something to do with your disappointment in the castines function.

I have my stove temps always around 400-600. The stack temps should have been a lot higher. If your stack temp is 450, your stove seems too cold. Or am I missing something?

Carpniels

PS. what does a stack thermometer look like? How does it work? Never hear it was possible except with a magnetic surface thermometer, similar to the one you put on the top of your stove. But then that will not work with a double wall pipe.

 

[begreen]

Good question. With the 602 I only had the magnetic surface thermometer. The temps for the 602 are surface temps, single wall pipe.

The Castine has double-wall pipe, so I have a Condor probe thermometer. This stove also has a stack damper at MSG's suggestion. The stack temps run about 50 degrees below the top temp if the damper is open and at about 100-150 degrees cooler with the damper closed. The damper is partially closed when the stack temps are above 350 and fully closed when the stove top is at about 500. The stove top temps we get are about 500-550 with soft maple and 600+ with madrona. And almost 700 if one isn't careful with Thomas's logs .

 

[pgmr]

I just checked the difference between flue gas temp and pipe temp on my stove - the gas temp on the Condar probe was 900F and the IR thermometer showed ~400 on the pipe right next to the Condar. The fire has been going for several days, so the pipe has had plenty of time to "get up to temp". It is single wall flex ss, painted flat black, so it's not a reflectivity issue with the IR therm.

Being the suspicious type, I inserted a K type thermocouple (attached to my multimeter) along side the Condar. The Condar was about 250F higher than the thermocouple. After testing the thermocouple in ice water and boiling water (within a degree F on each), I adjusted the Condar to match.

On the latest check, I had 600F on both the Condar and the thermocouple and 330F on the IR thermometer. So unless the IR is way off (which it doesn't appear to be based on some tests), there is still a significant difference between the gas and pipe temps.

The temperature right next to the inside of the pipe, but away from the probe hole (to keep room air from blowing on the thermocouple) was 425F when it had been 600F in the center of the flue. It would appear that a laminar flow exists and the hotter gases are toward the center of the flue.

 

[carpniels]

Hi Begreen,

OK. 500-700 top stove temp is what I used to get with my Castine. I have no idea about the flue temp. Does not matter to me.

I thought you might have been running your stove to cold and thus not getting the heat you want, but I was wrong; I misread the original email.

Sorry you are not the happiest castine uses. I hope your replacement will do better.

Carpniels

PS> Let me know if you want an Isle Royale. Shipping is a killer but I talked to my wife and we could make it our family vacation: a trip to WA by car. I have never been west of PA so it would be interesting. Take a week off, load the kids and stove in the car and drive west. What an adventure!!