High flue temps and how to solve them.

[oldspark]

Anyone else ever have really high flue temps and figure out why, most of the reported flue temps (most not all) seem to be a lot lower then mine. Tried different ways to run the stove but nothing helps much, with a bed of coals my flue temps go from 250 to 600 in less then 5 minutes with the stove still setting at 300 or so.
This is surface temp double checked with a IR testor.
When it gets real cold it just makes it worse, stove wont heat the house very well and I have a hot fire which means I have high flue temps.
Had this problem with 2 different chimneys,.
If I could turn back time I would have put in a new 8 inch chimney and stuck with the Nashua.
Now have the 6 inch I would not have any idea if there is a stove I would like better.
When the below 0 temps pass it wont be as much of a poblem but for now its a bummer.

 

[Hardrockmaple]

Buy a large Drolet. My flue temps never/ever goes over 400 and it takes 15-20 mins. to get there even with a bed of hot coals.

 

[oldspark]

Buy a large Drolet. My flue temps never/ever goes over 400 and it takes 15-20 mins. to get there even with a bed of hot coals.

Well you are not the first one to have much lower flue temps then I have with different brands of stoves, begreen has much lower flue temps then I with basicly the same stove but not sure what kind of wood and how much air he is giving it.

 

[Highbeam]

With my old hearthstone I regularly ran the internal flue temps well into the 1200 range which corresponds with your 600 surface temp. It wasn't accidental though and more of a daily clean out practice. The stove temp was standard and always lower than the flue temp. Different stove designs send more heat up the flue for several reasons, that non-cat hearthstone wasted tons of heat up the stack.

 

[69911e]

How tall is your chimney flue?

 

[oldspark]

Total height is right at 18 feet I believe straight up, its funny it did the same with the block chimney with a 7 and 1/4 clay liner with 2 90's.

 

[oldspark]

that non-cat hearthstone wasted tons of heat up the stack.

I hear ya, my Nashua ran (and does) with cooler flue temps.

 

[madison]

Spark, I can't compare as i do not measure stack temp. Any possiblity of air entrainment other than the primary and secondary air ? As this would increase the volume of air (and heat) heading up the chimney.

The only reason I suggest the above is that I have removed my firebricks for cleaning and noticed stripped/loose bolts that hold the EBT (been that way since delivery) and believe that along with the ash chute is a source of air into my firebox. After ash cleanouts, I believe I can see slightly hotter burning in the area of the loose bolts and ash chute. Never been motivated enough to try to seal up the ash chute and loose bolts - I believe even with the ash chute full of fine ash, it still leaks, but is not as evident than after a clean out and refire.

 

[oldspark]

I could not see any signs of that madison (ash chute), I checked a couple of years ago as it was discussed on here before.
Ebt box looks OK.
Wife broke some fire brick so have to replace a few and will give it a once over.

 

[ddahlgren]

Is there some way to specify how the flue temp is measured? Either probe, IR or stick on magnetic...Without that the numbers are meaningless.
As far as high flue temps go unless intentional it usually means big fire box and not enough heat exchanger to catch the heat.

 

[oldspark]

In my OP I stated surface temp double checked with a IR testor.

 

[oldspark]

As far as high flue temps go unless intentional it usually means big fire box and not enough heat exchanger to catch the heat

Interesting you say that, big baffle spewing fire just a short distance from the stove pipe=high flue temps?

 

[MishMouse]

Make sure you keep an eye on your flue. I ran into an issue where I damaged the pipe by letting it get to hot.
Ways I limited this issue were to not run with full air when re-fueling, and close the damper half way to limit the amount of fire going up the flue.
Upon refueling the fire gets sucked up the flue due to draft which causes it to get really hot.

 

[oldspark]

Make sure you keep an eye on your flue. I ran into an issue where I damaged the pipe by letting it get to hot.
Ways I limited this issue were to not run with full air when re-fueling, and close the damper half way to limit the amount of fire going up the flue.
Upon refueling the fire gets sucked up the flue due to draft which causes it to get really hot.

Well I have tried about everthing, if I want a hot fire (to heat the house) I am going to have a hot flue.
I can live with the 600 degree flue temps but it just seems like they should not be that high but with a fire breathing baffle close to the flue pipe not sure how I can get away from it.

 

[rideau]

You really don't want to be running regularly with a 1200 degree internal temp. Aside from too much heat lost up the flue, and hence very inefficient heating of your home, I don't believe the pipe is designed to be run constantly at 1200. My internal probe certainly has that temp marked in the too hot range. I'd try, first, cutting the air down. I'd start shutting right away if loading in a coal bed. Watch the flue temp. As the surface thermometer goes toward 300, start closing the air a bit. Let the stove get up to temp slowly. You may find that if you can keep the flue temp down a slower fire will give you more actual heat for your home, because of less heat lost up the chimney. Seems counterintuitive to need a flue damper at 18 foot flue, but one might help, if you can put one in your install. The damper isn't very expensive and perhaps worth a try/

 

[begreen]

I curious whether the new Summit C design has reduced flue temps or not. There are more secondary ports in the new baffle design.

 

[oldspark]

You really don't want to be running regularly with a 1200 degree internal temp. Aside from too much heat lost up the flue, and hence very inefficient heating of your home, I don't believe the pipe is designed to be run constantly at 1200. My internal probe certainly has that temp marked in the too hot range. I'd try, first, cutting the air down. I'd start shutting right away if loading in a coal bed. Watch the flue temp. As the surface thermometer goes toward 300, start closing the air a bit. Let the stove get up to temp slowly. You may find that if you can keep the flue temp down a slower fire will give you more actual heat for your home, because of less heat lost up the chimney. Seems counterintuitive to need a flue damper at 18 foot flue, but one might help, if you can put one in your install. The damper isn't very expensive and perhaps worth a try/

Been there done that, everything you mentioned I have tried at least dozens of times, removed the damper after playing with it for a year.

 

[oldspark]

You really don't want to be running regularly with a 1200 degree internal temp

No biggie that high heat is only for a few feet, it tapers like a turd before it gets into the class a pipe.

 

[oldspark]

I curious whether the new Summit C design has reduced flue temps or not. There are more secondary ports in the new baffle design.

Me too, would like to hear how it compares to the older models.

 

[oconnor]

How high up are you measuring the flue temp? 600F doesn't seem too high for me in the first two feet above the stove. I'm surprised though that you are getting temps that high on the pipe, but not in the stove - or more to say that the stove temp seems cool.

Are you running the blower on the stove right away after reload? I wait until my insert top reaches 500 or more before I turn the blower back on.

 

[oldspark]

Maybe my temps are not that high but many on this forum have reported much lower flue temps with fairly high stove top.
18 inches above stove, the stove top does come up although much slower then the flue, maybe I am reading the wrong posts.
No don't run the blower until temps get up to 500 or 600.
Sure wish some more who claim low flue temps would chime in.

 

[tahoostas]

Hey Oldspark
I have an Alderlea T5. A typical load for me sees the double wall (outer, IR) get up to about 130c (266F) and once it's settled in usually lingers around around 100c (210f), maybe a tad higher on big loads. That's with stovetop around 260c (500f) during the best part of the burn, again these go higher if I pack it up for a big burn.
Double wall to chimney. Total length about 14', straight up. Burning ash and poplar. Bloody cold weather, -30c all week.

 

[begreen]

You need a probe thermometer to read double wall temps. Surface temps on double wall are not too helpful. They vary directly with the distance from the flue collar.

 

[oldspark]

Those temps on double wall are fairly high so you might be seeing the same temps I am.
Its obivious that many have the same temps I do so I guess I am not that far from normal, maybe the ones with really low few temps are not the norm.

 

[ddahlgren]

Interesting you say that, big baffle spewing fire just a short distance from the stove pipe=high flue temps?

Well yes I do say that and a short coming of the company that designed it. It tells me thew stove has a very low thermal efficiency no matter how good the combustion efficiency might be. With those temps to the moon you are burning wood for no good reason at all. The other thing is the minimum air setting might not be closed enough and no way to get the flue temps in the range of reason. If the stove can not give a stove temp well above the flue temp it is a poor design period. Sure not on start up but when cruising it should be that way. Mine cruising will be 450 with a probe and 550 to 600 on the stove top using a very accurate probe made for industrial processing. During thwe coaling stage I see 450 stove and 300 flue or something similar with that ratio. Lacking doing anything else I would at least put one of the old heat reclaiming things that go in the stack and get some of that heat in the house.