Is it possible for too much air to cause a fire to burn poorly

[SurfPine]

ATVs, small engines, etc. tend to use a crude speed-density injection system (without O2 sensor feedback), so they don't adapt as well as automotive systems.

I believe fixed jet carbs are of the devil, but in the case of fixed jets, some benefit can usually be gained by lowering the float level in the carb, though it can be a more difficult, trial and error filled approach compared to simply changing jets. A proper air box shouldn't be restrictive, so the recommendation to drill it seems a bit odd, but if it works...

Yeah, my Grizzly only has a barometric sensor and no O2 sensor for adjusting fuel. I did add an O2 sensor for my AFR wideband but that is for my understanding of the ratio, not for automatically adjusting fuel. Per the gen, I actually have two that I can run in parallel but at 9500 feet, one generally never needs air conditioning other than getting an open window cross wind going for ventilation. I have no need for running a microwave and wish I had a need for a hair dryer. So I generally only ever need small amp output anyway but also installed a solar setup to recharge the 6V golf cart house batteries. My gens are typically for backup as I'd much rather listen to river water than annoying gens, even though mine are inverter gens and somewhat "quiet". My goal is to never have to fire the gen(s) up.

So a good burn can be done at that altitude.

Indeed, although I'm at 1000 feet lower. The Lopi Answer-95 (non-cat) stove at my house burns extremely well and is very easy to get a fire started. It is not a main heat source so I only burn occasionally but I am surprised how easily it gets going and then I can load it and then turn down the input air, no smoke. Seems I do have good exhaust draft on mine.

 

[vdavidoff]

This morning I added 3' (and bracing) to the stack. We'll see how things go. I plan to keep using the stove as I have been and see if I notice any differences, before changing anything else. Started getting ~40mph gusts right about the time I was finished, and the bracing appears fine. So, fingers crossed that I see some improvement in some way.

Before and after.



Andy

 

[stoveliker]

Maybe a naive question, but your flashing on the up side of your chimney seems to not do much this way? (It seems to end above the roofing.)

 

[begreen]

Hope that helps. If it does, you might want to switch everything topside to class A chimney pipe with an anchor plate. That will keep the flue gases hotter which will help draft and reduce creosote buildup. Is the 6" chimney liner for the Kuma insulated?

 

[vdavidoff]

Maybe a naive question, but your flashing on the up side of your chimney seems to not do much this way? (It seems to end above the roofing.)

If I understand what you're referring to, that's just how it was when I bought the house, and when my installer put in the insert and chimney and such they didn't mention anything about it. I am not sure I understand what you mean exactly, though - are you talking about the flashing keeping snow off the masonry?

Andy

 

[vdavidoff]

Hope that helps. If it does, you might want to switch everything topside to class A chimney pipe with an anchor plate. That will keep the flue gases hotter which will help draft and reduce creosote buildup. Is the 6" chimney liner for the Kuma insulated?

Yeah, I feel pretty good about what I have done here. I may not be a pro but I think it's a few steps beyond being a hack - but I imagine my chimney sweep (same people who did the install) will want to redo it come spring. Which is totally fine by me.

 

[stoveliker]

If I understand what you're referring to, that's just how it was when I bought the house, and when my installer put in the insert and chimney and such they didn't mention anything about it. I am not sure I understand what you mean exactly, though - are you talking about the flashing keeping snow off the masonry?

Andy

Yes; water running down from your roof to your masonry chimney does not get diverted before it hits the stones. From what I can see the seam is caulked or so?

I'm no expert, but it looks fishy to me.

 

[vdavidoff]

Yes; water running down from your roof to your masonry chimney does not get diverted before it hits the stones. From what I can see the seam is caulked or so?

I'm no expert, but it looks fishy to me.

I added some sealant a few years ago because I was getting some minor leaking, but I never swung back around to address it in any larger sense. I'll ask my chimney sweep and the guy who does most of the work on my home about it, though. I appreciate the suggestion.

 

[vdavidoff]

Hope that helps. If it does, you might want to switch everything topside to class A chimney pipe with an anchor plate. That will keep the flue gases hotter which will help draft and reduce creosote buildup. Is the 6" chimney liner for the Kuma insulated?

Sorry, missed this question the other day...Best I can tell the 6" liner is corrugated single wall. The corrugation stops near the top of the chimney and the pipe sticking out into the air is smooth single wall, I believe. There may be a corrugated layer on the inside of it, if I remember correctly, though, but that ends where my next extension begins, and it's smooth single wall from there up to the cap. The liner in the masonry, that you can see from inside the home lookup up the chimney, you can see the corrugation on the outside of it, and it's semi-flexible.

 

[vdavidoff]

After two weeks with the additional chimney height I think I can comment on it.

The extra 3 feet seems to have made a significantly positive difference, but I still have to use the tricks I have learned along the way to ensure the fire burns well.

If I keep making fires the way I have been recently, with the additional height in the chimney I seem to see a pretty consistent, significant increase in cat and blower temps, and durations of those temps, and though I still get some smoke, it seems to be significantly reduced and in some cases clears up into nothing visible way sooner than it otherwise would.

As far as specifics with regard to draft, my calculations (accuracy questionable) suggested the additional 3' would gain me ~16% more draft, and that seems to be about right on. I am consistently measuring ~.02 inches of water column more that before increasing the chimney height. Where before a good burn would read about .08-.09, now I'm reading .10-.11.

That I am burning pine, and that some of it is pretty pitchy even for pine (even though it seems to be seasoned relatively well) seems to me to be the biggest factor in terms of when I do get a load that seems to not perform as well as I think it should. I haven't noticed this in previous years, but this year I do occasionally wind up with some surprisingly wet, sappy looking residue at the chimney cap. I sent a picture of it to Jason at Kuma and he indicated:

That type of creosote is common with some pine varieties that have a high pitch/resin content. We see that a lot with a pine species here we call Ponderosa or Bull Pine. We advise people to steer clear of those pines whenever possible and only use them if absolutely necessary and only if dried for a minimum of one full year.

Adjusting the intake is still surprisingly touchy - there are times when even super small adjustments make a huge difference, but I suspect there's a lot of overlap there, again, with the quality of the wood at that time.

I swept the chimney a few days ago and though at the very top of the cap there was some thick, hard nasty stuff, what came out of the rest of the chimney was minimal, so that was good to confirm, since there was one or two really smokey runs even with the higher chimney.

So, I think short of doing something like installing a powered draft inducer, which I'd like to avoid for a few reasons (namely that I'm concerned the amount of creosote I seem to generate would destroy it, and they are too expensive to risk that), this is probably as good as it gets short of totally redesigning the chimney or stove, neither of which I think is necessary especially considering the work and expense that'd take. For good measure I do plan to have my installer/sweep redo my work professionally this spring.

At this point the only thing that bothers me is that sometimes when I reload the stove, if there are a few fairly large chunks of wood still in there burning really slowly, I'll get that smoke back into my house when the door opens. I suspect this is just a matter of the chimney being mostly cool compared to the firebox and the inside of the house. I don't really have any good ideas about this yet other than trying to time reloads and calculate loads so that I don't wind up with enough fuel still in there, but a cold enough fire, that this is a problem. Considering the timing like that basically works, but it's not foolproof. This seems kinda dumb but I am considering rigging a little stand/holder for my stove vacuum so that maybe I can suck that smoke into it, where it'll at least get filtered before it's exhausted, rather than just letting all that go wherever it wants in the house.

 

[stoveliker]

After two weeks with the additional chimney height I think I can comment on it.

The extra 3 feet seems to have made a significantly positive difference, but I still have to use the tricks I have learned along the way to ensure the fire burns well.

If I keep making fires the way I have been recently, with the additional height in the chimney I seem to see a pretty consistent, significant increase in cat and blower temps, and durations of those temps, and though I still get some smoke, it seems to be significantly reduced and in some cases clears up into nothing visible way sooner than it otherwise would.

As far as specifics with regard to draft, my calculations (accuracy questionable) suggested the additional 3' would gain me ~16% more draft, and that seems to be about right on. I am consistently measuring ~.02 inches of water column more that before increasing the chimney height. Where before a good burn would read about .08-.09, now I'm reading .10-.11.

That I am burning pine, and that some of it is pretty pitchy even for pine (even though it seems to be seasoned relatively well) seems to me to be the biggest factor in terms of when I do get a load that seems to not perform as well as I think it should. I haven't noticed this in previous years, but this year I do occasionally wind up with some surprisingly wet, sappy looking residue at the chimney cap. I sent a picture of it to Jason at Kuma and he indicated:



Adjusting the intake is still surprisingly touchy - there are times when even super small adjustments make a huge difference, but I suspect there's a lot of overlap there, again, with the quality of the wood at that time.

I swept the chimney a few days ago and though at the very top of the cap there was some thick, hard nasty stuff, what came out of the rest of the chimney was minimal, so that was good to confirm, since there was one or two really smokey runs even with the higher chimney.

So, I think short of doing something like installing a powered draft inducer, which I'd like to avoid for a few reasons (namely that I'm concerned the amount of creosote I seem to generate would destroy it, and they are too expensive to risk that), this is probably as good as it gets short of totally redesigning the chimney or stove, neither of which I think is necessary especially considering the work and expense that'd take. For good measure I do plan to have my installer/sweep redo my work professionally this spring.

At this point the only thing that bothers me is that sometimes when I reload the stove, if there are a few fairly large chunks of wood still in there burning really slowly, I'll get that smoke back into my house when the door opens. I suspect this is just a matter of the chimney being mostly cool compared to the firebox and the inside of the house. I don't really have any good ideas about this yet other than trying to time reloads and calculate loads so that I don't wind up with enough fuel still in there, but a cold enough fire, that this is a problem. Considering the timing like that basically works, but it's not foolproof. This seems kinda dumb but I am considering rigging a little stand/holder for my stove vacuum so that maybe I can suck that smoke into it, where it'll at least get filtered before it's exhausted, rather than just letting all that go wherever it wants in the house.

I'd avoid the vacuum; don't want to be encouraging gases to come out when you open the door...

 

[vdavidoff]

This is still driving me insane but I have some updates.

Just as a point of information, I had the 3' extension I added replaced with a 4' one with proper bracing and such.

A few weeks ago the flexible inner liner became detached from the solid liner that goes out the top of the chimney. After that was repaired the stove runs better than I think it ever has. An amazing difference in the strength of the draft and cleanliness of the fire. For about 10 days I thought all my problems were solved. I am wondering if that connection has been poor for years and that has been screwing up my draft in an insidious way, but I'll never know.

However...awesome burns like that are spotty. Things will be fine for some variable number of days, then all of a sudden they'll suck again. And usually shortly after they suck I get up and check the chimney, and it's clogged nearly beyond belief.

Because of how well the stove runs now (when it runs well) I think I'm down to environment or wood as continuing problematic factors.

I still believe my wood is seasoned properly and shouldn't be causing issues. The guys who installed and service my stove and chimney have seen it and they agree it seems fine.

I have a new theory and as usual I'm probably thinking too hard but I wonder how this sounds to anyone:

I have high, consistent winds here all the time. 20-40mph gusts all day with 10 minute average speeds of 20mph are very common. Sometimes I have gusts closer to 60-80 mph. I have a vacu-stack on the top of my chimney and when the wind picks up, the draft definitely picks up - I don't have any issues with downdraft.

I am wondering if between those high winds (i.e. high induced drafts) and the size of my firebox (very large, and I fill it up), what's happening is that the wind induced draft is igniting more fuel than the natural draft of the fire can feed, and when the wind dies down, even for a few seconds here and there (it's usually blustery even when it's windy all day), the fuel that can't get fed by the natural draft smolders, which backs up the chimney with smoke, which cools the chimney, which kills the draft even further, etc.

Any thoughts on that? I'm still grasping at straws here.

Thanks as always.
Andy

 

[begreen]

At 9500' you are dealing with multiple confounding factors. The altitude, the cold, and the wind. The add a cat stove with cooler flue temps. The flue system needs to be tuned to deal with these extremes.

It sounds like the flue setup is cooling down the flue gases too much. The liner in the chimney should be insulated. The exterior piping should be insulated, class-A chimney pipe, not rigid single-wall chimney liner. The object is to keep the flue gases hot, above 250º, all the way to the top of the chimney. This keeps the flue gases below the creosote condensation point and also keeps the draft stronger. That last stretch of extension pipe is acting like a giant heatsink. Cat stoves tend to run with a cooler flue output temperature. With the lower temperature output from the cat stove, the liner + extension is cooling down the flue gases too much. That's why the sudden creosote accumulation. Also, the liner moves. It expands with heating and contracts with cooling. That pulls against the rigid connection to the extension. There are better solutions.

Just to verify, is this an insert in a fireplace, or a freestanding stove?

With high winds, the vac-u-stack cap is creating a too-strong draft. I suspect that with a fully insulated liner and class A chimney extension, that cap will no longer be necessary and that a high wind cap may be preferable.

 

[vdavidoff]

Thanks for the thoughtful reply.

This is a Kuma Sequoia being used as an insert. About the last 6 feet of chimney is packed with insulation as of a few weeks ago, but the rest of the chimney is uninsulated. Prior to that only about the last 2 feet of the chimney was insulated. It is a relative large masonry chimney FWIW.

The pipe out the chimney is for sure not double wall, it's just a rigid single walled pipe. I don't know how it's rated. I have very recently considered replacing it with something I know is class A insulated/double walled but didn't pull the trigger yet. I had also considered removing that extension entirely (understanding how it's dissipating heat) and hoping that I don't _really_ need it, but that's a lot of height to lose in terms of impact on draft. I'd rather spend the money on the right type of piping first and see what happens.

Interesting point about flue temps on cat stoves - if I engage the cat, even if the firebox and cat temps are great, the problem is definitely considerably worse, until a significant amount of fuel has been used up. Also note that when it starts backing up with smoke, if I crack the door, the fire will rage, so it definitely seems like it's starved in those situations.

The build up is definitely right where the stove pipe goes out of the chimney and becomes totally uninsulated in the outdoor air, so that threshold does definitely seem like it's where the problem is, as you've described.

Andy

 

[begreen]

At 9500' the stove will need about 4' more than at sea level. The minimum suggested in the manual is 12', so that can be used as a guide. What did Kuma say about connecting the stove to a 6" liner instead of 8"? The manual repeatedly says only use 8".

Note that single-wall pipe is not allowable for any chimney application per the stove's manual.

 

[vdavidoff]

The chimney height with the latest extension is about 25 feet. Without it about 21.

Kuma did indicate using a 6" pipe would cause notable restriction, especially if using an offset box (which I am not), but they stopped quite short of saying it wouldn't work / is definitely a problem in this application. I don't think I ever mentioned to them that the extension was single walled pipe.

The issue with using an 8" liner is that it won't fit through the flue in the masonry chimney. I don't know how big a job it'd be to modify the chimney to make room, but that is always an option. I am pretty sure there's metal in that spot that's built into the masonry, so I think it might require grinding or cutting, but I am not sure.

Andy

 

[begreen]

I hear you. 8" flues are a pain, especially for inserts. They have become quite uncommon for inserts.

Do you know the tile liner ID for the chimney?

 

[vdavidoff]

I don't know the ID. I think most of it will fit 8" liner fine, but it's the flue area (sorry if I'm using the wrong term) from the old fireplace that's the problematic restriction, and that may even only be because of the angle the pipe has to take through there. I haven't had my head in there since before the stove was installed, of course. I'll find out what my stove guys think about getting an 8" liner in there.

Until I can make more changes I'm going to see what happens if I just load the firebox less. It wouldn't surprise me if I still get pretty long burn times assuming that allows me to avoid the smoking and all that causes.

 

[begreen]

I was just wondering whether it is square or rectangular. Sometimes an ovalized liner can fit where a round one can't. But if it's square then it doesn't matter.

 

[vdavidoff]

The tight spot is, as I recall, rectangular. On the topic of oval liners, what's the consensus on how the difference in shape, assuming the same volume, impact draft?

 

[RockyMtnGriz]

I don't know the ID. I think most of it will fit 8" liner fine, but it's the flue area (sorry if I'm using the wrong term) from the old fireplace that's the problematic restriction, and that may even only be because of the angle the pipe has to take through there. I haven't had my head in there since before the stove was installed, of course. I'll find out what my stove guys think about getting an 8" liner in there.

FWIW, I probably wouldn't be willing to invest significantly more in a stove that gives me nothing but problems. That's essentially what you'd be doing by installing an odd-duck size liner to suit this stove. If it works, great, but if it doesn't and you decide to replace the stove, you're probably going to want the smaller liner you have now. A bit of a gamble.

Personally, I think I'd first try snooping around the neighborhood to find a setup that works well and I thought I could duplicate with the existing flue and just a new stove.

I've posted quite a bit on this thread already, as I have a similar situation. I've been quiet lately, as I've been giving the new cat a chance to break in, and since this is an occasional use stove for me, that's taken a while. At this point, I'll add that everything I've done to improve the draft, mostly by sealing the flue, has been positive. Changing out the cat of unknown history that looked fine both physically and per the temps achieved on the cat thermometer, has turned out to be a game changer - much better performance. It's unfortunate that your cat change didn't help.

The most recent experiment has been changing the diet from lodgepole pine to douglas fir (not the pitch laden stuff from distressed trees). Surprisingly, that seems to make a big improvement in the way this stove processes wood as well. Lodgepole is just SO flashy. Doug fir loads have less smoking during the burn, require considerably less adjustment of the draft, and give much more consistent cat and flue temps with slower rise and fall through the cycle. That all adds up to being farther from the conditions that give rise to bad behavior like smoking and backpuffing.

I imagine that doug fir is not so available in CO, but I do remember from my days there (and I get a tiny bit of it here as well) that there's three kinds of aspen:

1. Green, and still too wet, but it'll burn.
2. Greenish, just cured, but has a flashy nature especially early in the burn.
3. Gray, stood dead in the forest for a long time, and burns more consistently, like (what I would call a "real") hardwood.

I have a tentative theory that most stoves are designed around the behavior of doug fir at the fast burning end, to eastern hardwoods at the slow burning end, and lodgepole or hot aspen is a bit off the chart on the fast side for a lot of them, particularly the cat stoves. It also makes sense to me that altitude would tend to decrease the secondary oxygen supply, making for a bad combination.

I'm wondering if you have noticed any difference between loads of freshly cured aspen and the older gray stuff?

 

[vdavidoff]

Thanks for the thoughtful reply. I do burn a bunch of deadfall aspen from my property early and late season (for whatever reason...) but it's all the gray stuff. It burns hot and fast as you'd expect but does also cause the same issues with smoke and puffing, sometimes. It seems to be less problematic than the pine I burn as my primary fuel, but it does still smoke like crazy sometimes. Even stuff that's long dead...there's no way it's too wet.

You're right about the stove. I am really being stubborn about wanting to get this to work but I am considering switching to a stove made for a 6" liner. I'm still waiting to hear back from my stove guys to see what they think about the possibility of going 8" before I make any decisions, though.

 

[vdavidoff]

Just because I like putting a nice cap on stuff like this:

I replaced the Kuma Sequoia (with the improperly sized liner, 6" instead of 8") with a Timberwolf T25i (also sold as the Napoleon S25i), which is made for a 6" liner (the largest diameter I can get through my chimney), and the difference is amazing. My burns are all super clean, way hotter, the glass stays clean, there's hardly ever any smoke out of the chimney, etc. Once the fire's going well (which takes no time, at least compared to what I was used to) I can run the box with the intake at the minimum setting and the fire is still just great. I also personally like that it's not a cat stove, just one less thing to fuss with. Watching the flames out the air tubes is very cool.

I would like to reiterate that if I had the Kuma installed correctly, I believe it would be a great stove, and their customer service is outstanding. If I could have got an 8" liner installed, I would have done so and kept the Kuma, but it wasn't an option.

I guess this is just a lesson in how much not following the manufacturer's guidelines can wreck a stove's performance. "Duh", I know, but anyway, maybe this'll help someone. At least I learned a lot in the process.

Andy