Question about secondaries

My own experience is about like many others have posted - I need some primary air and flame to keep things hot enough and keep enough gas coming from the wood to support secondary burn in my stove. However, you asked if a secondaries-only burning is the only way to have an efficient burn (or something to that effect). First I think we have to agree how to measure efficiency. I think an efficient burn means completely burning the wood, thereby getting the most heat possible and emitting as little burnable wood particles or gases as possible from the flue. I guess other definitions of efficiency include getting the most heat from the stove, using as little wood as possible to heat your house, and probably others.

Any time you have enough air to fully combust the wood you should achieve maximun efficiency. If that happens in a crazy firebox-filling inferno or if it happens at a slow rate shouldn't change the efficiency. With a really hot fire you probably have a chance of gases coming out of the wood too fast for the secondary air supply, not fully burning all the gases and losing efficiency. WIth a lower burn you have the chance that temperature in the firebox isn't hot enough to burn all the gases, or the gases are not concentrated snough to support combustion, so gases escape and you lose efficiency. However, it soulnds like with your stove you can set the primary air low and still have steady secondaries, so you are probably getting high efficiency. I think there are others ways you could get similar efficiency as well.

For the sake of the discussion, last night I had the draft all the way down and a crazy fire still going on, after burners kicked in and all sorts of flame on the wood, I reloaded at about 300 and shut the air down at about 450 or so. First time I had that happen, damm crapppy Oak. :lol:

BrowningBAR said:

SlyFerret said:

BrowningBAR said:

SlyFerret said:

I think achieving a burn with secondaries only for hours at a time is unrealistic (in a non-cat stove at least). We seem to have had a number of new members/burners confused lately.

Cutting the air back far enough to run with secondaries only, with nothing but smolderibg splits isnt going to keep the firebox hot enough to support the secondaries that long, and you will end up with noting but smldering splits.

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I disagree with this, at least as far as running a Hearthstone is concerned. I cut the air controls off and close a pipe damper. Burning hot I will get a 5 hour of useable heat with temps topping out at 600+ degrees and they will remain 500+ degrees for 3+ hours. Most of those three those hours will be with secondaries. The other 2+ hours will be with flame and occasional secondaries.

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You get almost 3 hours with secondaries ONLY? No flame coming from the splits at all?

-SF

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"Most of those three those hours will be with secondaries."

See this thread for how my secondaries look when the stove is looked in and humming along. The final two images is how the stove runs for the most part of three hours.
https://www.hearth.com/econtent/index.php/forums/viewthread/83823/

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Good pics! I'm not saying you can't have secondaries for that long. From those pics, it looks like there is still a little bit of flame coming from the splits, not just smoldering them with the ONLY flame being the secondaries.

-SF

Scott2373 said:

Here is my stove burning with secondaries only in the first video, then a little flame in the second. Read the descriptions under the videos for details. This was when I went to bed and the next morning I had about 1-2 inches of glowing coals. Please excuse my heavy breathing in the videos, LOL %-P
Video 1

Video 2

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The second video is what I'm talkin' about! Just enough air to sustain a little bit of flame from the splits to help make sure the firebox stays hot enough to keep the secondaries stable.

-SF

All the temperature references above would seem to be totally specific to a stove model.
To be able to have secondary combustion, one of the necessaries is >1000 deg F where the secondary flames would be. Kinda hard to simplistically measure that, eh? Maybe you can evolve some rules of thumb, or just check the condition of the secondaries.

You also need volatiles from below. This depends very much on firing rate and MOISTURE in the wood, for a sustained burn. Moisture BAD.

To get all this to work cleanly and efficiently requires a competent operator. The major source of fun for us is learning how to become one. Any idiot can light a gas burner.

SlyFerret said:

I think achieving a burn with secondaries only for hours at a time is unrealistic (in a non-cat stove at least). We seem to have had a number of new members/burners confused lately.

Cutting the air back far enough to run with secondaries only, with nothing but smolderibg splits isnt going to keep the firebox hot enough to support the secondaries that long, and you will end up with noting but smldering splits.

For a non-cat, the most efficient burn will be acheived when the air is cut back as far as you can and still maintain stable secondaries. At this point, there will almost always still be a little bit of flame coming from the splits. Go too far and the secondaries go out when the firebox temp starts to drop.

-SF

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+1

This is exactly how I've been running my Englander 30-NCH. I give it enough air to maintain the firebox temps up enough to keep the secondaries going. With my set-up, there ain't no cutting the stove all the way down, but depending on the outside temps, I can get close - but that ain't my goal. I'm trying to achieve a zero smoke out the chimney clean burn. I have found that I need to give my stove a bit more air than just enough to maintain the secondaries via firebox temps in that I need to have enough air to maintain that temperature up to the coaling stage. As the wood depletes, but not at coaling stage, it needs more air to maintain the same heat as a freshly loaded firebox. I don't want to constantly adjust the damper - but rather set it and forget it until the next reload, so I give a bit more air from the get-go and let it stay there until the end of the burn. I'm probably using a bit more wood this way, but I am getting a clean burn from start to finish.

Bill

Hankjones said:

Can someone please post a short video of what their 7+ hour secondary burns looks like? I can't for the life of me get that kind of burn. I'm maxing maybe 2hr with little flame off logs and secondaries cooking. If anyone has time it would be REALLY helpful for us new people to get a shot of what things look like at hour 1,3,5,7. Most of the time by 3 hours I just have no flames with a ton of red coals. Sometimes I get a bit more flame by playing around with the primary air after 2hrs or so.

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That is a video that will never be posted. :exclaim:

Milt said:

Hankjones said:

Can someone please post a short video of what their 7+ hour secondary burns looks like? I can't for the life of me get that kind of burn. I'm maxing maybe 2hr with little flame off logs and secondaries cooking. If anyone has time it would be REALLY helpful for us new people to get a shot of what things look like at hour 1,3,5,7. Most of the time by 3 hours I just have no flames with a ton of red coals. Sometimes I get a bit more flame by playing around with the primary air after 2hrs or so.

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That is a video that will never be posted. :exclaim:

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From reading the description in the video posted above, it looks like secondaries from 12:30 to 7:30.... That's an awful long secondary burn.

I get real slight secondary burn around 300.I have the Rangeley.I haven't experienced much for cold weather so haven't stoked her up much.I did have an inferno going at about 600 but had to slack it back because we got hot fast.I have noticed that ya do need an open flame to keep these secondaries burning for any length of time.(No flames,short secondary burn).The happy medium seems to be we'll say an 8" long flame and about 4"high.Say like maybe at least 1 log out of 3 burning half decent.JUST AN ESTIMATE.Stove top temps i haven't experienced enough with but i'm gonna say around 500 to 650 to have em stay running like a blast furnace.Best i can describe.I have to run this thing at 275 to 300 for shoulder burns.It's what keeps this place comfortable,just have to clean chimney more i guess. I have noticed fallen fine pieces that have fallen out of stack into the stove that looks like the asphalt pieces from a shingle.It's hard and dry and fine.Is this creosote?

Both of my non-cat stoves can (and often do) run with the air control all the way closed (as much as the EPA will allow, anyway) once properly heated up, this results in mostly secondary burn but of course there is still some primary air and some primary flame. More so in the Napoleon than the Ultima, which really does run close to secondaries only. It can be a tricky business knowing when it can be turned down that far, though. Do it too early and there's not enough positive feedback to sustain the fire, and it smolders. Do it too late and the fire is going to burn faster than I might want. Best approach is to change the control in steps, but that requires more fussing.

No 7-hour secondaries here, BTW. A few hours max.

Scott open the top of your stove,with a flashlight look back in and see if you see anything that fell out of the pipe.Tell me what ya find. Thanks.

Long fires at High Altitude (about 5350 ft.): Our stove has a large firebox. With the primary air shut to minimum, we can maintain secondary-only burn, but only for about 45 minutes, max. And, when you go downwind from the house, the stove exhaust smells acrid and the chimney shows smoke, although very light. If we open the primary just a little bit -- and it is very, very sensitive to small changes -- we get a mixed primary and secondary flame, with no smoke visible at the chimney, and a pleasing aroma smelling slightly like coal. The mixed primary/secondary will burn for 3 to 4 hours. The final, secondary-only flame will survive about an hour longer, before leaving glowing coals. We can get useful heat 'til morning with residual coals enough to ignite reloaded wood.

With a non cat, I do not think a secondary-only flame over baking/coking coals is feasable for more than a couple of hours max -- at any altitude. There isn't enough radiant heat from the baffle and secondary tubes to keep the coals "venting" any longer. In any case, the "mixed-fire" seems more efficient, although not nearly as entertaining/sureal! Cheers.

I've seen secondary action start with stove temps still well under 300. Scott, your videos show your Rangeley burning in the same manner that mine does. I have to occasionally run with the primary 1/3 to 1/2 open due to some less than perfect fuel. With dry wood the stove doesn't mind having the primary air cut back well before 500 degree temps and can cruise just under 400 if you get it just right with awesomely dry wood. I haven't gotten secondaries for more than 2-3 hours and once the wood is charcoaled thoroughly and burning clean, I don't worry about it. I worry more about long burns that don't boil me out of the house. Can't wait to get some real cold to let this beast run a little.