Overnight burn: second half no fire despite perfect first half - normal?

[yuryk]

Dear comminuty!

I seem to found a way to properly start those "overnight" fires, so having air control almost closed, it looks like this:

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It continues like that for about 2-3 hours with properly working secondary burn and no smoke from the flue. But then the fire disappears leaving only glowing stuff looking like this:


Because of this overall temperature drops, secondaries stop working and smoke appears. So at this point I have to open air control to get the fire back. But if it's an overnight burn, obviously, I can't do that. So very often in the mornings I just find a small bunch of lightly glowing coals left and the glass sometimes pretty dirty since the fire disappears early.

My question is: do you guys have it like this too? I would think it might be due to the not properly seasoned wood again, but it looks pretty nice in the beginning few hours, so I'd think it should continue like that... But it doesn't...

Thank you.

 

[EatenByLimestone]

Moisture content does have an affect on this.

Species does too. Some woods don’t coal much at all, whereas some seem to immediately coal and sit like that for the rest of the burn.

Once the volatiles burn off, you generally get coaling from hardwoods. The temp goes down. If the stove is sized right, this normally isn’t an issue, but can be if it’s really cold and you need heat NOW. Again, wet wood causes issues as it jumps to coaling faster and then doesn’t want to burn up as quick.

 

[Northern NH Mike]

I burn almost exclusively maple and that cycle is what I typically see. Flames for two hours with very low airflow. I get a good pile of coals that go for another two to three hours. The exhaust temp goes down as measured by the probe thermometer in the stack, but the stove temp cruises along nicely. I typically reload after five hours when the stove temp drops and the coals have collapesed to ash. For ano overnight burn after six or seven hours I am usally left with some coals that will restart a load of scraps or fat wood and then the cycle starts again.

 

[NickW]

For me, I get my stove under control after startup with the damper almost fully closed and the air at 1/8 open. After about 1 1/2 hours it is settled in and starting to drop so I open the damper a little to 3/4 closed and the air to 1/4 open and get a couple more hours of secondaries. As stated above, mc can have an effect as well as species and quantity.

 

[MrCampbellAHS]

What species are best for good sustained overnight burns? I'm burning mostly White Ash that tests somewhere between 8 and 15% and I get results similar to the original poster. I've been able to extend by setting the initial burn back sooner and that produces what look like bigger coals, but the cat drops fairly quickly so I know I'm not getting a great secondary burn.

 

[NickW]

White ash is the best of the ash species. I burn more of that than anything. I find a few chunks of better stuff on the sides and across the top of my "tunnel of love" (oak, sugar maple, beech, locust, hickory, ironwood, etc) helps control and extend the burn. Ash lights and burns well, but doesn't coal really long. It releases it's BTU's quickly compared to some of the other hardwoods.

 

[Wisco Shepherd]

I burn almost exclusively maple and that cycle is what I typically see. Flames for two hours with very low airflow. I get a good pile of coals that go for another two to three hours. The exhaust temp goes down as measured by the probe thermometer in the stack, but the stove temp cruises along nicely. I typically reload after five hours when the stove temp drops and the coals have collapesed to ash. For ano overnight burn after six or seven hours I am usally left with some coals that will restart a load of scraps or fat wood and then the cycle starts again.

This is also my experience with maple, particularly with silver maple which was nice to get ahead on wood as it seasons quickly but hasn't been all that impressive.

 

[BillBurns]

I myself dont do over night burns. Im too paranoid.

 

[MrCampbellAHS]

White ash is the best of the ash species. I burn more of that than anything. I find a few chunks of better stuff on the sides and across the top of my "tunnel of love" (oak, sugar maple, beech, locust, hickory, ironwood, etc) helps control and extend the burn. Ash lights and burns well, but doesn't coal really long. It releases it's BTU's quickly compared to some of the other hardwoods.

So you do a layer of Ash followed by one of those other hardwoods for overnight? That may work for me as I have the hook up on a place with a variety of other hardwoods. It may not do me any good this season, but for next season...

 

[NickW]

So you do a layer of Ash followed by one of those other hardwoods for overnight? That may work for me as I have the hook up on a place with a variety of other hardwoods. It may not do me any good this season, but for next season...

Sometimes. It depends on what sizes I have of which woods. I typically go 4 pieces north/south across the bottom with a tunnel between the middle two. The middle two are always large ash chunks. If I am looking for the best longest burn the tunnel cap is something better and each side gets a piece of better stuff and fill the gaps with ash or other midgrade. If the outside better stuff is on top it burns a little hotter, if the outside better stuff is on the bottom it coals longer. I generally just fit the outside pieces the best way possible, but prefer the better stuff on the bottom. Ironwood or hickory outside bottom will still be a in log form but solid coals in the morning. Nice to reload on.

 

[MrCampbellAHS]

I found some decent pieces of thorn in my stack that I'm going to experiment with tonight. Unfortunately my firebox won't allow me to go north/south as you describe, but I think I may be able to replicate it to some degree by simply layering thorn (and maybe a piece of Black Walnut?) and White Ash.

 

[MrCampbellAHS]

So at least some partial success. I got about 8 hours using this method: loaded at 8pm with 2 or 3 pieces of some old, but well seasoned, hardwoods from last year (hard to tell species and I didn't think to take pics) l, then a couple pieces of my good White Ash, then a piece of mixed with a good solid piece of thorn, and topped off with a couple sticks of ash again. Got the catalyst up to about 3/4 and really shut it back hard right before bed. I checked it at about midnight: really good coals, catalyst dropped to just below half. All I did was Crack the air intake just a touch more. Woke up just now, and it was ashed over, cat down in the inactive range, but decent coals underneath. I've got 4 piece ls of ash on right now trying to get the cat up before I go back to bed. I think I needed for finish with another hardwood and that would have helped, also better timing of the load (maybe wait until the kids go down at 8:30-9pm). Also I have some short splits of ash that I use to start new burns that I may try on the second layer north/south in-between layers of hardwood. Still, thanks for the idea NickW.

 

[Wisco Shepherd]

So at least some partial success. I got about 8 hours using this method: loaded at 8pm with 2 or 3 pieces of some old, but well seasoned, hardwoods from last year (hard to tell species and I didn't think to take pics) l, then a couple pieces of my good White Ash, then a piece of mixed with a good solid piece of thorn, and topped off with a couple sticks of ash again. Got the catalyst up to about 3/4 and really shut it back hard right before bed. I checked it at about midnight: really good coals, catalyst dropped to just below half. All I did was Crack the air intake just a touch more. Woke up just now, and it was ashed over, cat down in the inactive range, but decent coals underneath. I've got 4 piece ls of ash on right now trying to get the cat up before I go back to bed. I think I needed for finish with another hardwood and that would have helped, also better timing of the load (maybe wait until the kids go down at 8:30-9pm). Also I have some short splits of ash that I use to start new burns that I may try on the second layer north/south in-between layers of hardwood. Still, thanks for the idea NickW.

Sounds like you are making progress yes overnight burns are a bit of an art the late timing for starting the burn definitely helps I've been caught starting a burn at 5:00 and then having my stove still be too hot to add more wood right before bed. Sometimes I'll do a very small fire just have a coal bed for an overnight burn

 

[EatenByLimestone]

That 5 pm need for heat is a tough call! I love having some pine, poplar, willow, etc handy for those times. It burning down gets rid of coals too.

 

[Northern NH Mike]

That 5 pm need for heat is a tough call! I love having some pine, poplar, willow, etc handy for those times. It burning down gets rid of coals too.

Are those of who who are using multiple species cutting your own firewood? The concept makes a lot of sense to me; having a variety of types available for different times of the day, or parts of the season is like having the proper tool for a job and not having to use a hammer for every situation. I'm stuck having to have mine delivered and 90% being maple.

 

[NickW]

I would say so. Not enough demand and $ for the low BTU woods to justify the space and effort for vendors. A mid-size load of smaller splits of maple loaded at 5pm can be ready for an overnight reload.

 

[MrCampbellAHS]

I'm cutting my own. I rely on local farmers and landowners I know of who have trees already felled or who have some that need felling. I have a little bit of wooded area that I own, but not much that needs cleared at the moment. That being said, there is a LOT of White Ash in my area, so that is predominantly what is available to me, but I try to find different stuff when and where I can.

 

[stoveliker]

The other way is to get used to heat output and fuel usage rates, and to use that to load the appropriate amount of wood to be ready for the next reload at the desired time.
No need for mixing species then.

But this requires some experience.

 

[NickW]

The other way is to get used to heat output and fuel usage rates, and to use that to load the appropriate amount of wood to be ready for the next reload at the desired time.
No need for mixing species then.

But this requires some experience.

Experience and premium wood. Guys with only oak and 3+ years ahead are living the dream. Premium wood for me is usually harder to get than the more mid-grade stuff like ash. Ash is great except for overnight when it gets really cold. Premiums have a longer effective heating cycle.

Right now I have more premium than mid grade which may give new owners here an issue in 2 years due to seasoning time. Having a hard time locating ash at the tree service pasture, but got a bunch of honey locust. Some sugar maple was mixed in with the low BTU stuff in the log drops I got. I try to give an extra year of seasoning because I split so big.

 

[JayMac]

Full disclosure: I'm really inexperienced, but here are my thoughts... My stove only looks like your first image when I have the air fully open. If I kept it looking like your first image for 2-3 hours, my stovetop temp (STT) would certainly be into overfire range.

I was told to get my STT up to 600-700 before shutting down the air. It usually only takes like 10 minutes to get close to 700, and then I have to close the air entirely or the temp will continue to rise/hold too high. (I typically check on it before I go to bed to make sure I didn't close the air too soon.)

Once I shut the air, things pretty much go black, and I trust/cross my fingers that things operate as they should. When I wake up and check on the stove maybe 10 hours later, my cat gauge is in the active range, and my STT is 400 or maybe a little under. Much of my glass will be really dark, but I think that's normal.

My novice hypothesis is that maybe you're burning your load too fully for too long, so the stove doesn't have enough to work with when you shut the air for the overnight.

 

[yuryk]

maybe you're burning your load too fully for too long, so the stove doesn't have enough to work with when you shut the air for the overnight.

Well, with the experience I have by now (2 months of burning ), I can certainly say that I'd never tell by a photo which air setting is used, because it really depends on the wood (how well seasoned is it). Sometimes "air" is fully open and there is barely any fire, looking as if the air is almost shut. But regardless, I think that tendency of temperature dropping after few hours and flames disappearing because of that - is there. Therefore, when fully loading during the day, my process now is the following:

1. Start the fire, leave the door crack open and wait for a roaring fire. Very much depends on the dryness of the wood, but on average about 10-15 minutes.
2. Close the door, air fully open - wait for full box of roaring fire with "bricks" formed on the logs. At that point the stove is pretty hot, so the secondaries can work.
3. Shut the air about half way (secondaries work beautifully when I do that ), then give it another 10 minutes, then shut as much as possible for the fire to be there. How much fire depends on the outside temperature, obviously, but most of the time it's minimum amount of slow and blue-ish fire.
4. At this point I'm simply maintaining that fire. In few hours it starts diminishing, so I have to start opening that air back little by little if I want that fire to be there as much as possible.
5. At some point the air is fully open again, then the last fire disappears leaving only glowing coals.

I'd have the same process for the night if I was making frequent trips to the stove, but I don't want to, so the fire disappears earlier...

That's how I see it at the moment. When I just started this year, I tended to shut the air too quick, because I wanted that "long overnight burn" So my glass was very dark every time this way and stove temp was not high enough to make secondary combustion happen. Now I rarely have black glass, mostly when logs are very close to it.

 

[NickW]

I was told to get my STT up to 600-700 before shutting down the air. It usually only takes like 10 minutes to get close to 700, and then I have to close the air entirely or the temp will continue to rise/hold too high. (I typically check on it before I go to bed to make sure I didn't close the air too soon.)

Once I shut the air, things pretty much go black, and I trust/cross my fingers that things operate as they should. When I wake up and check on the stove maybe 10 hours later, my cat gauge is in the active range, and my STT is 400 or maybe a little under. Much of my glass will be really dark, but I think that's normal.

I run a tube stove and know very little about cat stoves, so kinda comparing apples to oranges, but...

I would be running insane flue temperatures if I waited for stt to be 600-700 before shutting the air down. On a reload on good coals with stt of 200 and flue of 300 I can hit 800 flue temperature before stt hits 350. I bet if I waited for stt of 600 I'd have a flue temperature over 1000.

My flue is rated for 1000 continuous, but I wouldn't want to do it. I've only hit 1000 once on a "takeoff event" prior to installing my damper and the stt was over 800. Boy was I sweating! I know a cat is a different animal (pun intended), but I wonder if waiting this long (stt 600-700) is sending a lot of extra energy up the flue. I have seen references to "the black box" on cat stoves...

 

[stoveliker]

The OP's signature says "w/o cat" though...
Regardless, it's hard to generalize because of flue height (draft) and fuel dryness will influence a LOT how (fast) a fire takes off, so when it should be dialed down, and how it behaves in the hours after.

 

[JayMac]

I run a tube stove and know very little about cat stoves, so kinda comparing apples to oranges, but...

I would be running insane flue temperatures if I waited for stt to be 600-700 before shutting the air down. On a reload on good coals with stt of 200 and flue of 300 I can hit 800 flue temperature before stt hits 350. I bet if I waited for stt of 600 I'd have a flue temperature over 1000.

My flue is rated for 1000 continuous, but I wouldn't want to do it. I've only hit 1000 once on a "takeoff event" prior to installing my damper and the stt was over 800. Boy was I sweating! I know a cat is a different animal (pun intended), but I wonder if waiting this long (stt 600-700) is sending a lot of extra energy up the flue. I have seen references to "the black box" on cat stoves...

It was the manufacturer who said to wait for 600-700 before shutting down the air for an extended burn, so I feel confident about doing that. He just said I shouldn't be repeatedly over about 800.

I do close the bypass much sooner (just a couple minutes after reloading onto hot coals), so the heat isn't going right up the flue at that point.

The manufacturer also said to focus more on the STT and the cat gauge than the stovepipe temp since I have a single-wall stovepipe. (I'm kind of cranky about that since the manufacuturer said they recommend double-wall, but my dealer/installer never even mentioned it. I would have said yes!) Still, I do watch my stovepipe thermometer too, and that actually hovers pretty consistently right at the low end of the burn zone. I had actually expressed concern that my flue temps were too low, and what the manufacturer told me is that as long as the cat gauge shows active, and I wait until 600-700 before shutting down the air, the pipe temp will be fine even if the thermometer I'm using says it's too low. (I did get an IR thermometer recently to doublecheck the pipe temp, and all seems okay.)

I appreciate your input. I have definitely been on quite the learning curve lately--just got this stove in November after using a worn out Dutchwest for a season--so I've been out here a lot to hear from others!

 

[JayMac]

The OP's signature says "w/o cat" though...
Regardless, it's hard to generalize because of flue height (draft) and fuel dryness will influence a LOT how (fast) a fire takes off, so when it should be dialed down, and how it behaves in the hours after.

Ah, see--I'm learning! And I was just looking at my own account and wondering what the "signature" is. Now I know to pay better attention to that.

OP, I'm sorry to have muddied your string. Please disregard anything I've said!