Stack Temps

[kopeck]

So I've been thinking....

I've seen folks talk about stack temps down around 300f. I've never seen that with my Tarm, I usually run a hair over 400f after a cleaning and it will climb up to over 500f and that's the point where I clean the tubes again.

I have turbulators and I make sure they get cleaned well each time I brush the tubes. I've never seen any real build up of creosote in the tubes, they brush out pretty easily.

I'm curious how some people get such low temps. Are they getting superior heat transfer or are they just measuring the temps differently then I do (I have an in flu gauge about 8" from the outlet).

K

 

[maple1]

I also have an in-flue guage, at about the same distance as yours.

I see about 200c, most times, at a decent burn. I think the sweet spot for mine with the natural draft is closer to 250c, burn efficiency wise, from what I have been told. I try to keep as many turbs in mine as I can while still able to maintain enough draft to my secondary chamber, that means I put more in in winter & take some out for shoulders. Kind of a catch-22 likely peculiar to natural draft. I never see any creosote in this area, or anywhere downstream of the wood chamber - just fine ash.

 

[Chris Hoskin]

kopeck,

400F is about right for the Solo Innova. In fact, it suggests you are using good dry wood and getting a good secondary burn. If you were to see 300F stack temps I would suggest your wood might not be as dry as it could be. The dry fly-ash you are seeing in the tubes and the easily cleaned turbulators are another good sign that you are doing everything right. Keep up the good work!

 

[Coal Reaper]

200-220*C here, mostly closer to 200. 240*+ and i brush the tubes. nothing but fine ash. last night though i was burning black locust for the first time and stack temp peaked at just about 250*C (tubes were cleaned sunday). man that stuff puts one killer flame through the hell hole!

 

[jebatty]

If the Innova is about the same as the Solo Plus, then you have another means to lower the flue temp some if you wish. The damper on the draft is adjustable to more or less open, more open is more draft and a faster burn and vice versa. For dry wood you may want a little more damped down draft, wetter wood the opposite.

I burn very well seasoned red and jack pine, and high burn temps are around 430-450F, and then the temp gradually falls as the wood load burns down. I have the draft damper closed down quite a bit.

 

[JP11]

I would say 350 to 380 is normal. I have the max set to 410. I see that when I stuff the whole firebox full and it's all roaring at once. Of course.. I'll see a 20 plus degree delta T.. with 25GPM.. so it's some serious heat.

JP

 

[kopeck]

kopeck,

400F is about right for the Solo Innova. In fact, it suggests you are using good dry wood and getting a good secondary burn. If you were to see 300F stack temps I would suggest your wood might not be as dry as it could be. The dry fly-ash you are seeing in the tubes and the easily cleaned turbulators are another good sign that you are doing everything right. Keep up the good work!

Thanks Chris,

I guess not all boilers operate the same. Sounds like Coal Reaper's Vedolux 37 runs about the same as my Solo Innova. I've never seen anything lower then 400 deg f. Of course who knows how accurate the gauge is, I'm sure it's with in the ball park.

The only time I've ever seen any creosote was at the end of last season when I was burning some junk wood. There was a few small spots on the turbulators. The tube brushed out clean. Typically I find only fly ash so I must be doing something right.

K

 

[KenLockett]

So I've been thinking....

I've seen folks talk about stack temps down around 300f. I've never seen that with my Tarm, I usually run a hair over 400f after a cleaning and it will climb up to over 500f and that's the point where I clean the tubes again.

I have turbulators and I make sure they get cleaned well each time I brush the tubes. I've never seen any real build up of creosote in the tubes, they brush out pretty easily.

I'm curious how some people get such low temps. Are they getting superior heat transfer or are they just measuring the temps differently then I do (I have an in flu gauge about 8" from the outlet).

K

Kopek, I had a mechanical gauge in my flue outlet for the past two years of operation and always thought my flue temps were high at 500-700 degF and sometimes as high as 800-900. At least according to the gauge. Well this season, I bought a probe type K thermocouple and temperature monitor and my flue temps range around 350 DegF when gassing solidly. Clean tubes of course as I just started burning for the season. I have a Tarm Solo 40 Plus and had been using the gauge supplied by Biomass USA. Anyhow, to make a long story short, I think those mechanical gauges are WAY inaccurate. There are other threads on the forum that confirm this.

 

[KenLockett]

Kopek, I had a mechanical gauge in my flue outlet for the past two years of operation and always thought my flue temps were high at 500-700 degF and sometimes as high as 800-900. At least according to the gauge. Well this season, I bought a probe type K thermocouple and temperature monitor and my flue temps range around 350 DegF when gassing solidly. Clean tubes of course as I just started burning for the season. I have a Tarm Solo 40 Plus and had been using the gauge supplied by Biomass USA. Anyhow, to make a long story short, I think those mechanical gauges are WAY inaccurate. There are other threads on the forum that confirm this.

By the way, I also have the Chain Type turbulators suggested by JE Batty also on the forum. Definitely brings the flue temps down I would say about 100 DegF.

 

[KenLockett]

By the way, I also have the Chain Type turbulators suggested by JE Batty also on the forum. Definitely brings the flue temps down I would say about 100 DegF.

Also have the fan damper choked down a bit as suggested by JE Batty as well. Burning 15-18% MC Beech at the moment and gassing very well at 350 DegF. Like Jim, as the load burns down the temps begin to fall.

 

[kopeck]

Also have the fan damper choked down a bit as suggested by JE Batty as well. Burning 15-18% MC Beech at the moment and gassing very well at 350 DegF. Like Jim, as the load burns down the temps begin to fall.

I have the Solo Innova, I don't have a damper. It's either on, or it's not.

The thermocouple is a neat idea, I never thought about that. Probably not nessisary but still a cool toy to have around!

K

 

[BoilerMan]

I have a K-type thermocouple just over the turbs inside the clean-out cover (wish I took a picture). I run in the 275F on a good roaring secondary burn. This has always seemed low to me, but I have grayish flyash in the firetubes and no creosote anywhere other than the fuel chamber. If it is not burning in the lower chamber 220F MAX, I don't know why other people's temps are higher.........burning mid teen moisture soft Maple right now, with some Aspen mixed in to get rid of it.

Fire-tubes: how many, what diameter, and how long in everyone's boiler?

Great thread K!

TS

 

[jebatty]

It's tough to compare boilers by stack temperature because there are so many variables at work: rated boiler output, species of wood, moisture content of each split, loose/tight wood load, size of splits, turbulators or not, draft, primary/secondary air flow, location where measurement is taken, accuracy of the measuring device, and more. Each boiler probably has a sweet spot, more or less, where everything purrs along. Assuming an accurate stack temp reading, a drop of 100F translates to about a 2-3% increase in efficiency in transferring heat to the water. But I think in all cases, only fly ash above the hx tubes, slight fly ash coating on the tubes, no creosote in the tubes or flue, good gasification through the burn -- all indicate a well performing boiler and reason to be well satisfied.

Incidentally, with my dry pine, I had stack temps 100F or more higher than now before stumbling on to the Chain Turbulator idea.

 

[woodsmaster]

The biomass I have has a max flu temp of about 380 at full bore when the tubes are clean, I've used different kinds of wood, thermometers etc. I have let it get up to 475 a couple of times before I cleaned it.

 

[KenLockett]

It's tough to compare boilers by stack temperature because there are so many variables at work: rated boiler output, species of wood, moisture content of each split, loose/tight wood load, size of splits, turbulators or not, draft, primary/secondary air flow, location where measurement is taken, accuracy of the measuring device, and more. Each boiler probably has a sweet spot, more or less, where everything purrs along. Assuming an accurate stack temp reading, a drop of 100F translates to about a 2-3% increase in efficiency in transferring heat to the water. But I think in all cases, only fly ash above the hx tubes, slight fly ash coating on the tubes, no creosote in the tubes or flue, good gasification through the burn -- all indicate a well performing boiler and reason to be well satisfied.

Incidentally, with my dry pine, I had stack temps 100F or more higher than now before stumbling on to the Chain Turbulator idea.

Jim,

I concur absolutely. I even tested the notion at the end of last season. After running with the Chain Turbs I did a cleaning and after cleaning the turbs decided not to put them in for the remainder of the season. Sure enough, tx increase at stack of approx 100 DegF. More of a pain to take out when cleaning but definitely would appear to improve efficiency so I have them back in.

Ken

 

[flyingcow]

So I've been thinking....

I've seen folks talk about stack temps down around 300f. I've never seen that with my Tarm, I usually run a hair over 400f after a cleaning and it will climb up to over 500f and that's the point where I clean the tubes again.

I have turbulators and I make sure they get cleaned well each time I brush the tubes. I've never seen any real build up of creosote in the tubes, they brush out pretty easily.

I'm curious how some people get such low temps. Are they getting superior heat transfer or are they just measuring the temps differently then I do (I have an in flu gauge about 8" from the outlet).

K

Same with me. Of course i have the same unit. 500-ish and i start getting ready for a scrub. Not uncommon to be 550/600 before i get to it.

 

[kopeck]

Same with me. Of course i have the same unit. 500-ish and i start getting ready for a scrub. Not uncommon to be 550/600 before i get to it.

I was waiting for you to chime in since our setups are pretty much identical.

Sounds like we run our about the same.

K

 

[Seasoned Oak]

I'm curious how some people get such low temps. Are they getting superior heat transfer or are they just measuring the temps differently then I do (I have an in flu gauge about 8" from the outlet).

K

The other day i put my hand on the flue pipe and found i could hold it there indefinitely about 3 Ft up from the stovetop measuring 400F.
I know this is a different kind of stove,but i thought that was pretty good heat transmission. Im going to take a reading with my IR gun next time to get the actual temps but it must have been no more than 150F.

 

[DZL_Damon]

I don't think you can read the exhaust temperature with an IR gun with any linear relation to a probe. My stack temp on my 3" long probe into the stack can be 185*F on my pellet boiler at mid fire, but I can put my hand on the pipe with no issue. An IR gun will only read 100*-110*F on the outside of the black stove pipe. I believe this is due to quasi laminar gas flows in the exhaust pipe, or at least a stagnant gas layer on the outter extremeties of the diameter of the pipe.

Most the gasses are moving through the middle of the pipe. Gasses clinging to the the pipe are pretty stagnant and act as an insulative layer. In thermodynamics for boiler heat transfer, the stagnant gas layer is surprisingly the LARGEST deterrent to heat flow, even more than moderate soot and water scale accumulation.

The only accurate way to measure your stack temp is a probe IN the gas stream.

 

[maple1]

I know when I'm burning, the magnetic thermometer reads 100°c less than the probe thermometer that's beside it.

Never tried touching the pipe before - maybe I'll do that next burn. You've got me curious.

 

[sdrobertson]

It's tough to compare boilers by stack temperature because there are so many variables at work: rated boiler output, species of wood, moisture content of each split, loose/tight wood load, size of splits, turbulators or not, draft, primary/secondary air flow, location where measurement is taken, accuracy of the measuring device, and more. Each boiler probably has a sweet spot, more or less, where everything purrs along. Assuming an accurate stack temp reading, a drop of 100F translates to about a 2-3% increase in efficiency in transferring heat to the water. But I think in all cases, only fly ash above the hx tubes, slight fly ash coating on the tubes, no creosote in the tubes or flue, good gasification through the burn -- all indicate a well performing boiler and reason to be well satisfied.

Incidentally, with my dry pine, I had stack temps 100F or more higher than now before stumbling on to the Chain Turbulator idea.

Agreed. I look for a temp of 100 degrees over the water temp I want to put out. When it creeps above 120 then its time for a quick cleaning. I am burning a EKO 60 with one nozzle plugged so I have extra heat exchanger tubes so I have always ran around 280ish stack temps but only fly ash like jebatty states. The ash tells the story.

 

[kopeck]

I guess that's kind of what I was getting at. I wondered how many folk were using stick on thermometers vs. internal ones. Sounds like there's quite a bit of variance between the the two. DZL pretty much confirmed what I was thinking, only in a much more technically worded way. The folks that probably have the best idea are the ones with the fancy Lambda boilers.

Like others have said the lack of creosote probably mean a lot more then the temp it's self. Obviously two low a temp and you probably are not gassifiying, two high a temp and your probably not transferring heat well (dirty tubes). It does sound like some boiler do a bit better with heat transfer then other but there's so many other variables it's hard to really say.

I've been watching mine pretty closely since I started this thread and it's running right around 425 f, sounds like I'm pretty much spot on with my Solo Innova. Of course the stack temp is at room temperature right now with it being in the mid 50s out side!

K

 

[heaterman]

Draft can make a huge difference in flue temp and efficiency..........

 

[jon 2701]

Hello everyone, I have not been on for a while. I have a question regarding my max flue gas setting on my Vigas 25. If I set it at the max rec. setting of 392F. My flue gas will climb to 500F at times. Boiler is clean and I am burning a mix of beech.birch and red maple. at about %20 mc. Draft is within spec. It never runs at that 392 unless I am real close to max boiler temp of 195f. Even then it only comes down to maybe 430F. It seems that this would be inefficient. If I set my flue gas max to 310f. It never goes above 410 or so. It seems to be off by about 100f to the setting. I do not have turbulators and it has been this way since new. Any ideas?

 

[JP11]

I've seen temporary shoots over... but not like yours.

Is it gassing well? I think it wants a good flame MORE than it wants stack temp. I think a call to Mark would be in order. BUT... I would write down all of your parameters listed on the panel. In fact.. I'd make a log of a few hours of burn,

boiler temp, lambda, fan speed, shutter, and stack temp.

Do you have a barometric damper? maybe it's sucking air out of the boiler more than the controls want.

min fan speed setting?

JP