Closing damper earlier on Buck 91

[woodnt]

Hello,

Noobie cat stove owner here. My first real fire after the break-in runs went great hitting the 600 degree damper close in about 30 mins. I used kindling to get it there, but it never went to 1000 before closing the damper like it indicated it would.

The next burn, I never could get it above 500 with a nice fire going. My stove installer said I could close the damper at 500, so I did it, and it lit and was at 1000 in a few mins.

The last 2 startups, it was struggling to reach even 400 with nice fires going (flames all through the firebox). I closed the damper just to see what would happen and was at 1000 degrees in 5 mins.

I know a lot of fine and medium kindling burns faster/hotter, but what if I don't have access to that much kindling? Is it OK to close the main damper (cat bypass) at 400 on a well established fire? What about 200 on a nicely going fire to hold in the heat better and get it to light-off temp?

Is the above hurting anything? When I load it and go to bed, it will naturally go down past 400 and lower with the damper cat bypass already shut as the unit cools down. Is it terribly different with it heating up? If so, could someone help me understand the reason, please?

Kindly,
Nathan

 

[Mark N MO]

Hey Nate! Here's my humble opinion, I've done the same thing. When my 91 is sluggish getting the temp up before closing the bypass, I start closing the shotgun air control (left side). I'll close it down about half way, then start closing the primary control (right side). It slows the burn down, keeping more of the heat in the firebox a tad longer, hastening the increase to cat light. IMHO, closing the bypass early gets a buildup of junk on the cat surface. Then when the cat does get to temp, it burns off. You can see it if you look just above the heat shield. I don't think it's doing the cat any good.

The difference between closing it early, and the cat already closed when the temp drops is in the amount of stuff the cat has to eat. Early on in the burn, there's a bunch of it. That's the stuff that burns off the cat. As the fuel burns down there's less of it. I believe it's called offgassing.

We've had our 91 for 9 years. The manual has a bunch of good info, like recommended startup and catalyst maintenance. I downloaded a copy from here, http://buckstove.com/manuals.html , and refer to it often.

Hope this helps. Your mileage may vary, don't take a wooden nickel, not legal for sale or use in CA, WA, OR, all the usual disclaimers.

 

[woodnt]

Mark,

Thanks for the thoughts. I'm sorry I was slow to respond back.

It is hard for me to imagine getting 1000 quickly as the manual said. For kicks I put in a lot of small to medium kidling to which it rose just a bit over 200. I sure would like to see a quick achievement of 1000 b4 closing bypass damper. After 30 to 45 mins sometimes it is nowhere near 600 or even 500 even though the box is filled with flame.

I'll keep it up and try to learn it and try to resist the urge to close the bypass at 400.

Kindly,
Nathan

 

[Woody Stover]

The next burn, I never could get it above 500 with a nice fire going. My stove installer said I could close the damper at 500, so I did it, and it lit and was at 1000 in a few mins.

I know a lot of fine and medium kindling burns faster/hotter, but what if I don't have access to that much kindling?

then start closing the primary control (right side). It slows the burn down, keeping more of the heat in the firebox a tad longer, hastening the increase to cat light

I had the 91 at my MIL's house, and would load on a 12-hr. schedule. When I got there to load, if cat probe temp was down around 250-300, I would burn several small splits (~3") in the front of the box to raise the temp which takes a while with that much heavy steel. I might only have the shotgun air open slightly, most of the air coming from the right airwash slider., but that only open maybe 1/2" or a little more. These settings will differ from stove to stove due to different chimney heights which determines draft, how cold it is outside (stronger draft,) etc. I wanted lively flame to generate heat, but wanted the air closed enough so I wasn't sending all the heat up the flue. I didn't notice a much faster warm up with bigger flames; Besides, I didn't want to overheat my liner with huge flame going up there for a long period. I would usually get the stove up around 700, then pull the coals to the middle and load the box fully, with only a couple pieces over the coals so that the flame could make its way to the top of the box and keep heating the cat area up. I usually wanted 900+ degrees before I closed the bypass, to ensure a quick cat light-off. I don't want a lot of unburned smoke going though my cat for long periods. I might keep the air open and lively flame going until the cat temp started to rise over 1000-1100. My final air setting was shotgun closed, right slider open maybe 1/4" or less.
If I loaded sooner than 12 hrs. I might still have 500-600 on the cat probe. In that case I might just put the full load directly on the coals after pulling them to the middle.
Now, if you are able to get a quick light-off at a lower temp, as indicated by a rapidly-rising cat probe temp up to 1000 or better, that's great!
I'll ask here, do you have good dry wood? How long has it been split and stacked in the wind? If some of your wood is only marginally dry, that may explain why sometimes you couldn't get the probe temp up over 400. For all modern stoves, cat or non-cat, you gotta have dry wood. Start splitting and stacking now for next season, get quick-drying stuff like Cherry, soft Maple etc. Oak and other dense woods should be segregated and saved for later seasons. Get small, dead trees with the bark gone...that stuff is pretty dry. If you are buying wood, get a moisture meter from Harbor Freight or Lowes, and go check the seller's wood before you agree to buy it. You need the wood at 50* at least, then re-split one of the big splits and jam the meter pins into the freshly-exposed face. A reading in the low 20s is passable, and that wood should be dry if you get it stacked in the wind now.
Another point (mentioned in the manual, I think) is to avoid excessive cat temps (1800,) which can shorten its life. I like to see my cats running 1000-1500.
I fought this because I didn't have great control of the air on the used stove I bought. Since control of the air wasn't the best, I learned early on to control the burn by how I loaded the stove. Pulling the coals to the middle and having coals under less wood, less of the load got burning at the beginning when I was trying increase temps and get the cat lit, and the load burned in a more controlled manner once I had the cat lit and cut the air to my cruise setting. Air control issues were that the ash pan gasket ends had unraveled slightly, allowing excess air to come in through the ash dump...coals were glowing more brightly there. Another problem was that my right slider plates were hanging too far away from the openings, letting too much air in, even with the slider closed all the way. This caused the cat to burn too hot due to excessive, uncontrollable gassing of the load. You can see these plates if you open the ash door and the fan control door, look up underneath the "hearth" or ash lip, and then operate the right slider. One way to get these plates to seal off the intake openings better would be to remove the plates from the right slider rod and pull the rod out. Then lay the middle of it across your knee and lightly press down on both ends of the rod, creating a slight upward bowing in the rod. That should hold the plates closer to the openings when re-installed. Don't over-do it or there will be too much friction when operating the slider.

When I load it and go to bed, it will naturally go down past 400 and lower with the damper cat bypass already shut as the unit cools down.

The difference between closing it early, and the cat already closed when the temp drops is in the amount of stuff the cat has to eat. Early on in the burn, there's a bunch of it. That's the stuff that burns off the cat. As the fuel burns down there's less of it. I believe it's called offgassing.

Nathan, do you mean that when you get up in the morning, cat probe is reading 400? That's normal because as Mark says, most of the volatiles are burned out of the wood at this point. If you have a lot of coals, you can pull them forward and open up the right slider air a little bit to help raise the stove temp and get you closer to where you need to be to reload.
The ash dump is pretty good on this stove. I had an L-shaped poker that slid down behind the back of the hinged lid to clear the ash and make the lid easy to open. Ash dump has a big opening and is off to one side, so I used the side of the shovel to save the coals over to the right side, then swept the ash down the hole. I burned three full loads, then emptied the pan. I never pulled the pan right after I dumped ashes out of the fire box; I pulled it right before a reload, when it was cooler.

 

[woodnt]

Wow! 12 hrs? I get 2 or 3 hours before I have to reload, but a lot of what I was burning was cut for a huge fireplace and is around 2 feet long so i have to angle it and then stuff smaller log in back (if I can) and in front. Hard to stack on top as I hit the ceiling as it isn't very tall.

A lot of the wood in using its 3 years (changed from hrs) old. Some came with the place, but I can tell it is dry (some super dry). I stage the wood on the porch so it doesn't get rained on (it can get "dewed on" in the morning, so I try to bring a day ahead into the house).

I usually load more logs when it gets to around 800. I try to run it around 1000. Sometimes it gets higher, but I've yet to see it over 1500, usually pegged in the middle in between 1000 and 1500 if it ever gets over 1000.

When I process the wood myself, I'll cut it where I can put me in there as my wife would love not to have to tend it so much while I'm at work.

I'm glad for the tip about leaving the right primary so closed. When trying to warm it up, I thought both shotgun and right primary are to be wide open, but closing to contain the heat but still get enough air makes a lot of sense. I'm eager to try that.

Thank you also for the mod, as in modification, (changed from mid) tip.

I have a meter on my wish list of purchases. I'll be buying some wood for next year, but also processing some naturally felled trees on our property. Getting the needed tools as I can.

Thank you so much for the input and shared experience.

BTW, 30 foot flue liner in the chimney. Drafts really well usually, but at little less so on the warmer days, as one would expect.

Kindly,
Nathan

 

[Woody Stover]

Wow! 12 hrs? I get 2 or 3 hours before I have to reload, but a lot of what I was burning was cut for a huge fireplace and is around 2 feet long so i have to angle it and then stuff smaller log in back (if I can) and in front. Hard to stack on top as I hit the ceiling as it isn't very tall.

You'll have to measure, but IIRC I think about 18-20" was a good length for N-S loading (front-to-back.) You don't want the splits too close to the glass, and you want to leave a little space at the back as well, so air can move around all sides of the load.
There wasn't a lot of heat coming off after 12 hrs. unless I had some of the more dense woods in there, but I was using wood I had cut for my stove...it was only 16" so I wasn't using all the space available. That space behind the 16" splits came in handy sometimes. If I had too many coals, I would shove 'em to the back, in that left-over space. Yeah, despite their claims of a 4.4 cu.ft. firebox, the actual usable space is closer to 3.

A lot of the wood in using its 3 hrs old. Some came with the place, but I can tell it is dry (some super dry).

Only 3 hrs. old, and super-dry? The weather must be very dry and very windy in OK.

I usually load more logs when it gets to around 800. I try to run it around 1000. Sometimes it gets higher, but I've yet to see it over 1500, usually pegged in the middle in between 1000 and 1500 if it ever gets over 1000.

That all sounds great! You may have better control over the air than I did at first, and you may not need to tweak the slider rod so the plates close tighter. You can probably even let the stove go to 500-600 before you reload, and still be able to load fully and get back up to temp without burning up too much of the load. Just pay attention to how much of the load has coals under it. You want a nice, controlled release gasses to feed the cat, not a ton of wood gassing, that may cause cat temp to go high.

I'm glad for the tip about leaving the right primary so closed. When trying to warm it up, I thought both shotgun and right primary are to be wide open, but closing to contain the heat but still get enough air makes a lot of sense..... hard for me to imagine getting 1000 quickly as the manual said. For kicks I put in a lot of small to medium kidling to which it rose just a bit over 200. I sure would like to see a quick achievement of 1000 b4 closing bypass damper. After 30 to 45 mins sometimes it is nowhere near 600 or even 500 even though the box is filled with flame.

My motto is "Good amount of flame in the box, with the least air possible." Like I said, when I put the main load in, I wanted to stack a few medium splits, loosely, in the center over the coals, where I could get good flame up to the heat shield and heat going toward the cat to help it light off. Then after closing the bypass, keep the flame going to it for a little bit until you get a strong light-off. If you don't get that strong light-off, and cut the air back too soon, the cat can crash on you occasionally, and the probe temp will keep dropping way under 1000. Not good, and could conceivably lead to creosote clogging of the cat over time. This was a rare occurance for me I want a quick light-off when I close that bypass, and a strong cat burn until the volatiles are spent out of the load.
As to the time needed, depending on how cold the stove was and how long I had to burn a few "sacrificial splits" to get the stove up to temp and get some coals to load on, it could be 45 min. to an hour before I had the cat lit, the air at my final setting and could walk away. You don't have to sit there the entire time, but if I wanted to leave the stove for several minutes I would always set the timer on my phone for 10 min. or so, to make sure I didn't space out. Once you load, the fire is constantly gaining in strength as more wood catches, and you have to cut the air every so often to keep building heat in the box, not sending it up the flue as draft strengthens. And above all, you do not want to overfire your stove or liner! If I heard that liner start popping, I knew I was tossing too much heat up there. You may have a different setup so the sounds may be different, but there will be sounds you'll hear that will help you run the stove.
Here's how my loadings went....yours will be different if you are getting quick light-off at lower temps:
I'd burn some "sacrificial splits" and get the probe up around 700-900 (also suggested in the manual.) Then I'd load the box and get some flame going up to the shield. I'd lose a couple hundred degrees loading, so I'd build temp back up to about 900-1000, then close the bypass and hopefully see the cat temp rising nicely before long. Sounds like you are lighting off well at lower temps so that's good!

Thank you also for the mid tip.

?

I have a meter on my wish list of purchases. I'll be buying some wood for next year, but also processing some naturally felled trees on our property. Getting the needed tools as I can.

If you cut your own wood, you take more care, and it's usually the right length. Wood-guy cuts can be hit and miss. If you are saying you've got some trees down now that need to be cut up, use the meter to help segregate the wood by dryness...upper branches will be drier. With Oak, you might see some rot in the sapwood, but the heartwood will still be solid fuel. You can post in the "Wood Shed" or "Gear" forums with any questions.
If you buy wood, check several guys out now and see if you can find some wood that they didn't sell and has been split since last year. A lot of these guys don't even split the wood until they are going to load and bring it over....not good! It will be laying around in log form but they will still call it "seasoned." BS.

30 foot flue liner in the chimney. Drafts really well usually, but at little less so on the warmer days, as one would expect.

I had the 91 on about 21' of stack. I'm curious about your setup and heat load. So the stove was professionally installed? Insulated liner in a fireplace, or is the stove set up to be free-standing with Class A chimney through the ceiling? Centrally located in the an open floor plan? How many sq.ft. are you heating? Insulation and air-sealing pretty good in the house?

 

[woodnt]

Woody Stover,

Thanks much again. We have the 91 as an insert professionally installed into our chimney. I'm not sure I understand the question about the heat load.

I don't know if the liner was insulated, but it was pricy stuff.

We live in a 2 story farmhouse modeled after a 1903 farmhouse but built in 2004. It is 3500 Sq feet of heated space. The fireplace is on a south outside wall.

Insulation is pretty good but they sourced vintage period doors, the the door seals could be better. Windows are modern duel pane. High insulation where it counts

Heats really well overall, but some days are better even preventing the upstairs HVAC from coming on most of the time. Some days it can burn us out even though the cat probe says 1000 but it seems variable in heat output with other days of similar outside temp struggling to even keep the down stairs HVAC off. Overall though, it does really great! I'm definitely pleased with the purchase. My wife? Not so much. Mess and she was expecting set-it-and-forget just like a thermostat on the wall.

My preference would have been free-standing to keep more heat inside, but the floor plan just didn't allow that to come to pass.

I just tried the closing the primary airs to keep in the heat. My wife hadn't managed it well so it was at 400 when I got home. Said it may have dropped a bit lower than that. I pulled out the bypasses. Loaded her up. Full open til things caught well. Closed shotgun and other primary half way after burn established and in 15 mins, it was almost 1000. BOOM! Closed bypass, began cutting back air further, and am waiting to cut it back more as I type.

I'm not an arborist, so I have no idea what kind of trees we have. Something else I'll have to fix. I'll figure it out, though.

 

[Mark N MO]

After reading the replies to this thread, I went and looked at the CAT thermometer. My Condor has a scale that indicates "inactive" below 500, "normal range" 500-1200, and "too hot" above 1200. I guess I've worked this stove so much over the years that I'd forgotten the light off temp recommendation. It's 500, and that's about where I close down the bypass.

"I just tried the closing the primary airs to keep in the heat. My wife hadn't managed it well so it was at 400 when I got home. Said it may have dropped a bit lower than that. I pulled out the bypasses. Loaded her up. Full open til things caught well. Closed shotgun and other primary half way after burn established and in 15 mins, it was almost 1000. BOOM! Closed bypass, began cutting back air further, and am waiting to cut it back more as I type."

I don't understand why you're waiting so long to close the bypass, or why you'd fully open the air controls with a temp of 400 on reload. Maybe I've misread something. When I reload at those temps, I don't open the shotgun, (left side) at all. I open the primary (right side) enough to notice the response of the coals indicating a good charge of air. It doesn't take long from there to get to light off temp and bypass closure. From there it's a dance to find the highest CAT temp with the lowest flame, by closing the primary control. For me, this gives the longest burn time.

The wood I get is cut and processed on our farm, red and white oak, hickory, and walnut. It gets cut to 18" length to fit front to back in the 91. All of it is dead standing, or blow-downs.

Our 91 doesn't have any air leaks. It can almost snuff out the fire by closing everything up. When it's cruising overnight with a full firebox, CAT temp is 800-1000, the shotgun air is completely closed, and primary air is closed to within 1/2" or so of shut. There is no visible flame. I have had to change the door gasket once, and the CAT once in the 9 years we've had it.

 

[Woody Stover]

Heats really well overall, but some days are better even preventing the upstairs HVAC from coming on most of the time. Some days it can burn us out even though the cat probe says 1000 but it seems variable in heat output with other days of similar outside temp struggling to even keep the down stairs HVAC off.

I think you'll get more consistent results, once you have your wood the right length to load N-S. Then you will have similar loads with similar burning and output characteristics.

When I reload at those temps, I don't open the shotgun, (left side) at all. I open the primary (right side) enough to notice the response of the coals indicating a good charge of air. It doesn't take long from there to get to light off temp and bypass closure.

If I was loading with the coals in the center, N-S, to get a burn starting at the center and working out to the sides, (like you see in the pic I posted in Nathan's other thread) I might use the shotgun air to get the center burning well, and not much other wood. The shotgun will focus the air and the fire in the middle, whereas the primary (airwash) will cause the fire to spread out more.

Our 91 doesn't have any air leaks. It can almost snuff out the fire by closing everything up. When it's cruising overnight with a full firebox, CAT temp is 800-1000, the shotgun air is completely closed, and primary air is closed to within 1/2" or so of shut. There is no visible flame. I have had to change the door gasket once, and the CAT once in the 9 years we've had it.

That's great...wish I woulda had that much air control at first! But yeah, my final cruise setting was usually shotgun closed, airwash open 1/2" or less, depending how cold it was out and how much draft I had that day. I might have some intermittent floater flames for a while if I wanted, or just go straight to cat only, no flame. Flame will eat some of the smoke and keep the cat temp a little lower until the flame goes out. Every fire is different though, you never really have total control...