Flue temp conundrum!

[oldspark]

For all you that read a lot of posts on here, I dont understand why some of the posts about flue temps say one thing and some say another, the recomendations are all over the place. Any one besides me have an opinion on this? One would think flue temps as far as saftey concerns should be in a narrow range but it goes from 500 (surface) :-S is the limit to "I dont care about no stinking flue temps".

 

[branchburner]

Have you been following the thread about Magic Heat? There's a bit of discussion about flue temps, among (many) other things. You may find it informative, or at least entertaining, though plenty of folks would say it is neither.
https://www.hearth.com/econtent/index.php/forums/viewthread/62231/

 

[Backwoods Savage]

Oldspark, do not forget we have lots of rookies on this forum. With that you will definitely get a lot of different answers. Some do one thing and it works so they think that is the only way. Some listen to Uncle Joe or Grandpa Jim and they used to burn wood 50 years ago so they know all about it. Of course you also have cat stoves and non-cat stoves which are definitely going to be different. And you also have people burning different types of wood, etc., etc.

 

[oldspark]

Backwoods, I am taliking about some of the regular hearth members and their opinions on flue temps not the new posters.

 

[Backwoods Savage]

Well, that is interesting for sure. I have noticed some but perhaps have not paid as much attention to it as I should. I'll watch for that and perhaps comment more later.

 

[begreen]

Haven't had to use a conundrum for years oldspark.

If the stove and pipe are installed correctly, clearances exceeded, and the temp is below the pipe rating I don't worry unless I don't know why the temp is high. I know the operation of our stove well enough by now that I have watched it cycle many times and it never stays up over about 700°F for very long. Then it settles down to around 4-500 for the long burn. The higher temps are always when I am either just starting the stove (hot first fire), or if I am pushing the stove, or have spaced out turning down the air control.

 

[johnstra]

I monitor my flue temps closely and I worry about them being too cool. This picture shows my approximate setup. The probe is about 14" above the top of the stove, but it's offset. When my stove is running at 450 on the surface, my flue temps are around 300. I have to work very hard to get mine up to 600.

 

[oldspark]

I monitor my flue temps closely and I worry about them being too cool. This picture shows my approximate setup. The probe is about 14" above the top of the stove, but it's offset. When my stove is running at 450 on the surface, my flue temps are around 300. I have to work very hard to get mine up to 600.

Wow, that is very low for a probe type sensor is it not? Is your chimney staying clean?

 

[gyrfalcon]

Haven't had to use a conundrum for years oldspark.

If the stove and pipe are installed correctly, clearances exceeded, and the temp is below the pipe rating I don't worry unless I don't know why the temp is high. I know the operation of our stove well enough by now that I have watched it cycle many times and it never stays up over about 700°F for very long. Then it settles down to around 4-500 for the long burn. The higher temps are always when I am either just starting the stove (hot first fire), or if I am pushing the stove, or have spaced out turning down the air control.

Oh, boy, how do you know what the pipe rating is? Mine (good quality double-wall) was installed by a pro three years ago, and I have no clue what the rating is.

 

[BrotherBart]

Haven't had to use a conundrum for years oldspark.

If the stove and pipe are installed correctly, clearances exceeded, and the temp is below the pipe rating I don't worry unless I don't know why the temp is high. I know the operation of our stove well enough by now that I have watched it cycle many times and it never stays up over about 700°F for very long. Then it settles down to around 4-500 for the long burn. The higher temps are always when I am either just starting the stove (hot first fire), or if I am pushing the stove, or have spaced out turning down the air control.

Oh, boy, how do you know what the pipe rating is? Mine (good quality double-wall) was installed by a pro three years ago, and I have no clue what the rating is.

99.99% that it is for no more than 1,000 degrees continuous. UL HT103 rating if I remember correctly.

 

[johnstra]

oldspark - I pulled my stove pipe off last week to seal the joints. I noticed a lot more accumulation than I expected. The stuff was crusty and came off very easily. So I'm afraid it's not staying clean. Not sure what to do about it.

If I run it really hard on startup once a week or so will that help to keep it clean? I haven't tried to get it up to 700 - seems like it would be really hard to do.

Suggestions?

 

[begreen]

Oh, boy, how do you know what the pipe rating is? Mine (good quality double-wall) was installed by a pro three years ago, and I have no clue what the rating is.

Very good question. A proper flue system is tested to UL 103 standards. It is designed for normal, continuous operation at 1000° F flue gas temperatures. Our flue (Simpson) testing also includes one hour at 1400° F, plus three, ten minute chimney fire tests at 2100° F.

Here's the regs:

UL 103
1 Scope

1.1 These requirements cover factory-built chimneys intended for venting gas, liquid, and solid-fuel fired residential-type appliances and building heating appliances in which the maximum continuous flue-gas outlet temperatures do not exceed 1000°F (538°C). Factory-built chimneys are intended for installation in accordance with the Standard for Chimneys, Fireplaces, Vents, and Solid-Fuel Burning Appliances, NFPA 211, and in accordance with codes such as the International Mechanical Code, the International Residential Code, and the Uniform Mechanical Code. They are intended for installation inside or outside of buildings or both, in a manner that provides a vertical (30 degree maximum offset) conduit or passageway to transport flue gases to the outside.

1.2 The chimneys covered by these requirements comply with either a limited duration 1700°F (927°C) flue-gas temperature test or a limited duration 2100°F (1149°C) flue-gas temperature test, at the manufacturer's option.

 

[ckarotka]

This may sound like alot of work but took the time check for smoke at various temps both sto e and pipe. I run the pipe at the lowest I can without smoke. For me it's 300 mag thermo single wall. If the stove however is crankin at 575 or higher I get great secondaries and the pipe can run cooler say 250.

 

[oldspark]

oldspark - I pulled my stove pipe off last week to seal the joints. I noticed a lot more accumulation than I expected. The stuff was crusty and came off very easily. So I'm afraid it's not staying clean. Not sure what to do about it.

If I run it really hard on startup once a week or so will that help to keep it clean? I haven't tried to get it up to 700 - seems like it would be really hard to do.

Suggestions?

Running it hard for an hour a day keeps the creosote away. Should not be to hard to get it up to at least 500 (probe) or so each day on start up or reload.

 

[gyrfalcon]

Oh, boy, how do you know what the pipe rating is? Mine (good quality double-wall) was installed by a pro three years ago, and I have no clue what the rating is.

Very good question. A proper flue system is tested to UL 103 standards. It is designed for normal, continuous operation at 1000° F flue gas temperatures. Our flue (Simpson) testing also includes one hour at 1400° F, plus three, ten minute chimney fire tests at 2100° F.

Thank you very much, sir. One more thing I was briefly worried about that I no longer need to worry about. It did get hot enough at a couple points last year when I was still fiddling with things for the ugly little metalized stickers that came stuck to it to partially char, curl up and fall off, but I know better how to keep it down now. (Happy to lose those damn stickers, though!)

 

[Todd]

Old Spark,
I think it's all a communication break down. Some people are taking flue temps with a magnetic external thermometer while others, mostly with double wall pipe are giving internal temps with a probe type thermometer. Many people just state their temps without saying whether it's external or internal. This is where I see a lot of confusion. Then there can be variables because of where the thermometer is located on the pipe, type of stove and also how much chimney they have.

I have used both and can tell you my Condar probe reads internal temps a little more than double the external single wall pipe temps when measured from a Condar mag thermometer. As external temps climb over 500 the internal probe reads even higher than double the external about 1100-1200. Last year Wess999 did a test with his thermometers and found the same along with a couple others.

Since I have single wall pipe I just use the external mag thermometer because I am convinced the Condar probe is not accurate in single wall, there is too much radiant heat off the pipe screwing with the coil on the probe, double wall is less effected by this.

Most magnetic thermometers are color coated and mine states too hot at about 550 so I'm thinking that is about 1100 internal which would be too hot continuously for a liner according to specs.

So for me when I see temps getting up near that external 500 mark I throttle down and since this only happens in the bypass mode on my cat stoves it usually tells me I'm about ready for the cat and after engaging those temps drop down to 230-350 depending on the burn rate I need. Hope this helps some.

 

[BrotherBart]

Well Oldspark since you are tangled up in your underwear about flue temps, think about this. A thermo 12 or 18 inches above the stove doesn't tell you one damn thing about the stack temp any farther up. 16', 20', 40' foot stack the temps are going to be different up there.

Rest. Go by what the stack looks like when you inspect it. If it looks like crap. Burn hotter. If it looks fine. Fugidaboutit.

And yes, I do not have a thermo on or in the pipes. Did it for a while. Don't need that kind of grief in my life.

 

[gyrfalcon]

Well Oldspark since you are tangled up in your underwear about flue temps, think about this. A thermo 12 or 18 inches above the stove doesn't tell you one damn thing about the stack temp any farther up. 16', 20', 40' foot stack the temps are going to be different up there.

Rest. Go by what the stack looks like when you inspect it. If it looks like crap. Burn hotter. If it looks fine. Fugidaboutit.

And yes, I do not have a thermo on or in the pipes. Did it for a while. Don't need that kind of grief in my life.

What you say makes sense but-- I didn't at all get the sense that Oldspark was tangled up in his undies about this, just asking a question. I thought it was kinda cool he'd read closely enough to notice that disparity in postings here and wondered why because I sure hadn't.

 

[BrotherBart]

Well Oldspark since you are tangled up in your underwear about flue temps, think about this. A thermo 12 or 18 inches above the stove doesn't tell you one damn thing about the stack temp any farther up. 16', 20', 40' foot stack the temps are going to be different up there.

Rest. Go by what the stack looks like when you inspect it. If it looks like crap. Burn hotter. If it looks fine. Fugidaboutit.

And yes, I do not have a thermo on or in the pipes. Did it for a while. Don't need that kind of grief in my life.

What you say makes sense but-- I didn't at all get the sense that Oldspark was tangled up in his undies about this, just asking a question. I thought it was kinda cool he'd read closely enough to notice that disparity in postings here and wondered why because I sure hadn't.

Oldspark has a lot of posts in the last two weeks about this subject. I hope he finds what he is looking for. So far I can't figure out just what that is.

 

[oldspark]

Well it looks like I am going to have to put together a group of posts, (if I can figure out how to do it), I have a PM thats interesting (not yours pen that was good) but will not do that to the person. If I can put some of them together I think you will see what I am talking about.

 

[fjord]

[quote author="oldspark" date="1289082788"]For all you that read a lot of posts on here, I dont understand why some of the posts about flue temps say one thing and some say another, the recomendations are all over the place. Any one besides me have an opinion on this? One would think flue temps as far as saftey concerns should be in a narrow range but it goes from 500 (surface) :-S is the limit to "I dont care about no stinking flue temps".[/quote]

That's me Sparky. Give credit where due. :lol:

The SOP for most: monitor your manufacturer's temperature locations and range. Burn correctly and cleanly. Use the best you can seasoned/dry wood, then enjoy the ride. Easy.
The proper burns lead to an anuual flue brushing result of perhaps a cup of dry, powdery soot from two flues.

In order to join the RWC (Real Woodburners' Club), shut OFF all central heating devices...now. Forget the "need" to keep all rooms @ 72 F. Cuddle under a high fill, pure goose down comforter with a one foot loft.
Open the window. That's the way in northern Europe. Why heat unused rooms ?

Now it's: " I don NEED no stinkin flue probes" .......or digital monitors, M², IR guns, Excel spreadsheets, 60" chainsaw, 90 ton splitter, etc.... Why ?

 

[corey21]

Mine runs about 200 to 250 flue temp. having problems getting it to 300.

 

[oldspark]

Mine runs about 200 to 250 flue temp. having problems getting it to 300.

That is interesting and you are not the first to report that, is that surfaceor probe sensor?

 

[Highbeam]

I monitor my flue temps closely and I worry about them being too cool. This picture shows my approximate setup. The probe is about 14" above the top of the stove, but it's offset. When my stove is running at 450 on the surface, my flue temps are around 300. I have to work very hard to get mine up to 600.

Something is funny then. I use a condar probe meter and every day run the flue past 1000 to keep it clean and burn off any funk from the startup. Easy peezy. Once running, in order to keep a clean burning fire, the probe meter indicates quite high (600-800) which might just be a shocking temp to some but do realize it is right in the freaking middle of the recommended burn temps on the face of the condar probe. If you can't run the flue temps this high then you need to consider wood size, wood dryness, and burn rate. Could just be that you need to run it harder, maybe your stove is oversized?

So here are a few reasons that the reported flue temps vary and why they vary with regards to stove surface temp.

1) Stone stove vs. steel. (I can be at 250 surface and 1100 flue, try that with a steel stove)
2) Cat vs. noncat (Cat flues will always be cooler once the cat is engaged)
3) EPA vs. smoke dragon (The dragons are capable of being choked down)
4) flue damper vs. clear flue.
5) probe meter vs. surface mount (This is the big one)
6) Folks burning clean vs. smoldering fires (to some folks you are supposed to smolder)
7) Reports of peak vs. sustained. (Sure, at times I am at 1000 or at 400 but mostly 600-800 during active burning)
8) Wet wood (you'll never get a good hot flue with wet wood)
9) oversized wood (also tough to get a hot flue)
10) location on flue being measured (I'm at 15" which is supposed to be equal to 18" on the directions from Condar, I called them first)

I love my probe meter. We use it more than the window to see how the fire is doing.

 

[corey21]

surface thermo probe above reeds 300 to 380.