Primary Air Igniting Gasses....this happen to you?

[kennyp2339]

I think I got my stove figured out.

I just wanted to say, I have been in your shoes before, tested my draft 2 years ago, same as you, had a excessive over draft (.18 on average) installed a collar damper and a key damper in my double wall pipe, I use the key damper as my primary damper and the collar damper for when the key is being environmentally overridden (arctic cold front nights) My stove is now a different stove, I get steady heat output, great burn times, predicted control and reduced wood consumption. Draft is key and when you have an over draft, you are essentially sucking up hot gases before the get a chance to absorb into the stove top and go into the room.
My house is also on top of a hill with prevailing winds that come from the west, northwest which is a swamp that has no tree coverage, so I get hit with a consistent constant wind in the winter.

 

[Woodcutter Tom]

I just wanted to say, I have been in your shoes before, tested my draft 2 years ago, same as you, had a excessive over draft (.18 on average) installed a collar damper and a key damper in my double wall pipe, I use the key damper as my primary damper and the collar damper for when the key is being environmentally overridden (arctic cold front nights) My stove is now a different stove, I get steady heat output, great burn times, predicted control and reduced wood consumption. Draft is key and when you have an over draft, you are essentially sucking up hot gases before the get a chance to absorb into the stove top and go into the room.
My house is also on top of a hill with prevailing winds that come from the west, northwest which is a swamp that has no tree coverage, so I get hit with a consistent constant wind in the winter.

Hey Kenny,
Any other information on how you operate your stove would be appreciated. It seems that you have the same scenario as me. I installed two dampers on my stove pipe; one is a Selkirk double wall damper assembly that has been enhanced with fender washers to slow the flow even more; the other is a damper that I installed in a section of double wall piper(Key damper). Both have the exact same round plate. I am always monitoring my manometer so that I am aware of the draft. A lot of the time the damper assembly is closed all the way so that I can keep the draft under .05 " WC. I have been able to reduce the heat going up the chimney by controlling the draft. Things are a lot better.
My concern is that I have not been able to achieve a 600 degree stove top temp. On occasion I still get the primary air from the above the door glass igniting the secondary gasses. See video. Once this starts, I have not found a way to stop it. The air burns the gasses and does not get to the bottom of the glass to clean it, thus creosote builds up on the glass. The residue is shiny and stringy when it cools down. This actually gives me my highest STT.

It will be warmer the next few days. I plan to fully inspect, adjust, or replace the door gasket and the door window seal.

Do you close one damper fully before starting to close the next one?
Do you have a target draft number you try to obtain?
Any thing that might be helpful would be appreciated. Thank you.

 

[kennyp2339]

A lot of the time the damper assembly is closed all the way so that I can keep the draft under .05 " WC. I have been able to reduce the heat going up the chimney by controlling the draft. Things are a lot better.
My concern is that I have not been able to achieve a 600 degree stove top temp. On occasion I still get the primary air from the above the door glass igniting the secondary gasses. See video. Once this starts, I have not found a way to stop it. The air burns the gasses and does not get to the bottom of the glass to clean it, thus creosote builds up on the glass. The residue is shiny and stringy when it cools down. This actually gives me my highest STT.

So the base line minimum is .05wc, and I on average roll w/ .08, I have similar results as your describing, keep in mind that the chimney is the engine that drives the stove, so weakening the draft directly correlates to a slower fire, which means lower stove top temps.
Now as for the secondary flames due to existing creosote build up inside the firebox, the build up is acting liking a catalyst in creating turbulence with the smoke on a hot surface, hence the mixture of air and it re-igniting, Professor Dick Hill from UM explains it better, but I suspect thats whats going on, which is good, before trying to adjust anything either add more air to the flow by damper adjustment or inspect the upper portion of the chimney and check for deposit build up, if nothing is occurring, dont fix what isnt broken.
As far as my damper operation, I have (2) but only use the 1 and as of right now that one gets set to 3/4 closed, the other damper is reserve for Nor'easter's when I get blasted with heavy winds off the mountain, thankfully I only have to deal with double downing dampers during storms and not all the time.
I should clarify something else, I strive for consistency, and since I did 1 full season of draft metering I can now judge my burns by rate, quality, stove top temps, ash vs coaling ect and tune my damper for a desired result without worrying about damage or diminishing the stoves capability, also when determining your draft you want your number in wc while the stove is wide open with a vigorous burn, then tune from that point.

 

[brenndatomu]

Many modern stoves/furnaces call for -0.04 to -0.06" WC for optimal draft...-0.08" is usually considered too much...I'm sure there are exceptions to this out there, but those numbers are very common.

 

[Woodcutter Tom]

Thanks Kenny,

Just to clarify, the creosote buildup is a direct result of the glass not getting washed. I start with clean glass. If the primary air ignites the gasses, the clean hot air does not keep the glass clean, thus it gets dirty and has creosote build up.

SBI informed me that the draft should be .02 - .03 " WC. I am trying different measurements as I strive for heat.

SBI felt that the secondary air was moving too fast, thus 'pushing' the gasses toward the front of the stove where they ignite when mixing with the primary air. I have a couple of tricks up my sleeve for slowing down the secondary air. With mild temperatures here it could be days before I have a fire and longer before test results are known.

Slowing down the draft has definitely improved my stove performance. I get longer burn times and longer mid-range heat. But I want the heat to warm up the house quicker.

So....Dear Santa, All I want for Christmas is a 625 degree STT. (I have not been too bad this year.)

Have a great Christmas.

 

[brenndatomu]

SBI informed me that the draft should be .02 - .03 " WC

Wow, that's low...more draft will provide a hotter fire, but also more heat up the flue too...

 

[MR. GLO]

I just wanted to say, I have been in your shoes before, tested my draft 2 years ago, same as you, had a excessive over draft (.18 on average) installed a collar damper and a key damper in my double wall pipe...

So when I use the damper and lower draft from .14 to .08 my flue temps drop too much...are you seeing the same results...can you explain when you adjust the damper and how long...
As the fire burns the draft changes and drops.

What are you seeing for flue temps in the coaling stage...and 350 stt...

 

[kennyp2339]

@MR. GLO I dont have a probe for my flue temps, While I'm burning I dont see really anything except heat vapors, occasional steam if the outside humidity is at the right spot, clean cap to, use to have to take my cap off mid season to brush crud, now that waits till the end of the season.

 

[neverstop]

Dragging this up before the season starts, but I see the air wash igniting off gassing as well. However, I see STT above 750 F and single wall surface temps of 500+ (so 1000+ internal) when this happens. Basically I see secondaries occur then eventually the air wash causes secondary combustion as well and the STT increases a lot when this occurs. I am confident that I do not have sufficient draft for my stove. My stove calls for 0.06-0.1" wc (hearthstone shelburn 8372); minimum chimney height of 16.5' from ST if setup in a rear exit configuration, 6" flue. I had a 5.5" uninsulated liner in a 16' external chimney with a rear exit setup. I haven't tested the draft, but I get smoke rollout when I open the door regardless of the stage of the fire with the bypass open. Currently upgrading the chimney system to fix this.

My thought process for why this was occurring; as I closed the primary air the total volume of gases going up the chimney decreased. This caused the flue to begin to cool (not insulated), which reduced the draft causing a reduction in velocity of the gases. Even though the STT and gasses were hot there just wasn't enough volume to keep the flue warm. Everything still went up the chimney, but there wasn't a lot of movement, so the stove got hot, the wood off gassed and any air introduced ignited it.

Do you have any issues with smoke rollout from the stove? The scenario sounds similar, except you're not seeing high STT. You're measuring STT on the ST and not the heat shield correct?

According to the manual for your stove the minimum chimney height is 12ft above the ST. Are you sure that the Mark II 25 is zeroed out correctly? (manual link: https://dwyer-inst.com/PDF_files/D_58.pdf) The accuracy of the reading for that gauge is +/- 0.09" wc (+/-3% full-scale of 3"wc). So it's not a very accurate gauge for measuring wood stove draft. Something like a Dwyer 2000-00 would perform better; it's full-scale is 0.25"wc and has an accuracy of 0.01"wc (+/-4% FS).

How does your stove perform with the longer chimney? I skimmed the posts and I couldn't confirm if you were having this issue with the primary air igniting secondaries at taller chimney heights.

 

[Woodcutter Tom]

Dragging this up before the season starts, but I see the air wash igniting off gassing as well. However, I see STT above 750 F and single wall surface temps of 500+ (so 1000+ internal) when this happens. Basically I see secondaries occur then eventually the air wash causes secondary combustion as well and the STT increases a lot when this occurs. I am confident that I do not have sufficient draft for my stove. My stove calls for 0.06-0.1" wc (hearthstone shelburn 8372); minimum chimney height of 16.5' from ST if setup in a rear exit configuration, 6" flue. I had a 5.5" uninsulated liner in a 16' external chimney with a rear exit setup. I haven't tested the draft, but I get smoke rollout when I open the door regardless of the stage of the fire with the bypass open. Currently upgrading the chimney system to fix this.

My thought process for why this was occurring; as I closed the primary air the total volume of gases going up the chimney decreased. This caused the flue to begin to cool (not insulated), which reduced the draft causing a reduction in velocity of the gases. Even though the STT and gasses were hot there just wasn't enough volume to keep the flue warm. Everything still went up the chimney, but there wasn't a lot of movement, so the stove got hot, the wood off gassed and any air introduced ignited it.

Do you have any issues with smoke rollout from the stove? The scenario sounds similar, except you're not seeing high STT. You're measuring STT on the ST and not the heat shield correct?

According to the manual for your stove the minimum chimney height is 12ft above the ST. Are you sure that the Mark II 25 is zeroed out correctly? (manual link: https://dwyer-inst.com/PDF_files/D_58.pdf) The accuracy of the reading for that gauge is +/- 0.09" wc (+/-3% full-scale of 3"wc). So it's not a very accurate gauge for measuring wood stove draft. Something like a Dwyer 2000-00 would perform better; it's full-scale is 0.25"wc and has an accuracy of 0.01"wc (+/-4% FS).

How does your stove perform with the longer chimney? I skimmed the posts and I couldn't confirm if you were having this issue with the primary air igniting secondaries at taller chimney heights.

This thread transitioned into this thread;

New Door Gasket- Fails Dollar Bill Test

I have been trying to get a better seal between my stove door and body. I seem to leak air from the bottom. I have done 4 replacements in the last 6 weeks. Some OEM, some aftermarket gaskets. Here is my latest with a brand new OEM gasket. The video shows how easy the bill pulls out. The...

www.hearth.com

Without having a good seal on the door, there was no way to tell if something else causes the primary air to ignite the gasses.
At the end SBI sent me a new stove. However it has a similar 'backward angle' on the lower section beneath the door opening. It might work for a while with the original gasket installed in the stove, but the SBI replacement gasket is totally different.
It will sit in my garage as I try other solutions provided by responses to the above thread.

 

[neverstop]

This thread transitioned into this thread;

New Door Gasket- Fails Dollar Bill Test

I have been trying to get a better seal between my stove door and body. I seem to leak air from the bottom. I have done 4 replacements in the last 6 weeks. Some OEM, some aftermarket gaskets. Here is my latest with a brand new OEM gasket. The video shows how easy the bill pulls out. The...

www.hearth.com

Without having a good seal on the door, there was no way to tell if something else causes the primary air to ignite the gasses.
At the end SBI sent me a new stove. However it has a similar 'backward angle' on the lower section beneath the door opening. It might work for a while with the original gasket installed in the stove, but the SBI replacement gasket is totally different.
It will sit in my garage as I try other solutions provided by responses to the above thread.

Understood, that is not my problem. Door gaskets are in working order. Not sure if there's a way to check the glass gaskets but those look fine as well.

 

[Woodcutter Tom]

To answer your questions from above:

I have dampers in my stove pipe. If I do not open the damper before I open the door, yes, I get smoke rollout. Otherwise, no smoke rollout.

I measure STT on the stove top, not the shield. I place a thermometer centered left to right and back next to the shield. I also use a IR thermometer to spot check areas of the stove top.

I periodically calibrate the Dwyer Mark II. I feel it gives me a reasonable reading. I was at .18 prior to installing the dampers. So being down in the .03 - .05 range is re-assuring.
I actually have a Dwyer magnehelic 2000-00. I have not used it. Perhaps I will build a box to hold it and install it this fall.

My chimney now is 14' above stove top. I was at 12' above stove top for some of last year, but I added back 2 feet since I was not properly above the roof ridge line. Yes, I did have the primary air igniting when I had a longer chimney. Late in the spring of 2021 SBI helped me determine that I had too much draft. Thus I cut down on the chimney and added the dampers.

My original door gasket was damaged on my first break-in fire. SBI wraps the ends of the gasket in tape. This tape melts and sticks to the stove body. When you open the door after the break-in fire, the tape sticks to the stove body. 1/2 inch of each end got damaged. I tried to plug the gap, perhaps unsuccessfully. The replacement gasket started the situation in my other thread.

What are you doing to upgrade the chimney system?
"5.5" uninsulated liner in a 16' external chimney with a rear exit setup." should get a bunch of attention here. Perhaps the chimney experts will chime in.

 

[neverstop]

To answer your questions from above:

I have dampers in my stove pipe. If I do not open the damper before I open the door, yes, I get smoke rollout. Otherwise, no smoke rollout.

I measure STT on the stove top, not the shield. I place a thermometer centered left to right and back next to the shield. I also use a IR thermometer to spot check areas of the stove top.

I periodically calibrate the Dwyer Mark II. I feel it gives me a reasonable reading. I was at .18 prior to installing the dampers. So being down in the .03 - .05 range is re-assuring.
I actually have a Dwyer magnehelic 2000-00. I have not used it. Perhaps I will build a box to hold it and install it this fall.

My chimney now is 14' above stove top. I was at 12' above stove top for some of last year, but I added back 2 feet since I was not properly above the roof ridge line. Yes, I did have the primary air igniting when I had a longer chimney. Late in the spring of 2021 SBI helped me determine that I had too much draft. Thus I cut down on the chimney and added the dampers.

My original door gasket was damaged on my first break-in fire. SBI wraps the ends of the gasket in tape. This tape melts and sticks to the stove body. When you open the door after the break-in fire, the tape sticks to the stove body. 1/2 inch of each end got damaged. I tried to plug the gap, perhaps unsuccessfully. The replacement gasket started the situation in my other thread.

What are you doing to upgrade the chimney system?
"5.5" uninsulated liner in a 16' external chimney with a rear exit setup." should get a bunch of attention here. Perhaps the chimney experts will chime in.

6" insulated liner, and adding 5 feet of class a above that for a total chimney height of ~21ft