Non-Cat Secondary Burn Questions

[leeave96]

When you burn a non-cat stove with secondary air tubes, I gather that you need to get the firebox up to around 1000 degrees for the smoke to light-off.

When the secondaries light-off, is the heat from the secondaries enough heat maintain the heat necessary to keep the smoke burning?

If secondary burn heat is enough to keep the smoke burning, then can you shut down the damper (I assume primary and maybe secondary dampers) such that you have a smoldering fire with very little flame - totally relying on the secondary burn to maintain enough heat to burn the smoke from the smoldering wood. Does this work?

The reason I ask is because I have a catalyst combuster stove, Woodstock Keystone and it will burn the cat brightly on pretty much smoke alone with a few red embers and no flames for a clean low burn.

I also have an Englander 30 non-cat stove that will get installed this fall. If the above is correct, then one could get a smoldering low burn while maintaining the secondaries (until the wood goes to charcoal and no more outgassing) not unlike a cat stove. The only difference is you have to get the stove up to a higher temp on a non-cat to light-off the secondaries, but then relying on the secondaries to maintain the heat necessary to keep the burn going, turn down the damper and let the stove cruise for a clean, long burn. Instead of a glowing cat burning the smoke, the secondaries burn the smoke.

We talk a lot about shoulder season burns being very easy to do with a cat stove, but I'm thinking the same is possible with the non-cat secondary tube type stoves like my Englander.

Have I got this correct or am I way off base?

Thanks!
Bill

 

[gdk84]

For me, I have no problems with secondaries with the air completely shut. It actually is a very impessive light show and almost seems a bit scarey when you first see them do there job. But it doesnt take long to sit back and crack that beer open and enjoy... Typically secodaries can last about 1/3 or more of the burn.

 

[begreen]

I can see you are thinking cat technology for non-cat burning. In practice, it's quite different. The interior of the firebox may be reaching 750F, but the stove top could be only 400-500F and still support good secondary combustion. Assuming there is proper draft, once they get burning, if the wood is dry, the stove temp will rise a bit and the secondary burn will continue until the wood has stopped outgassing. However, a smoldering fire is not what you want. It is more a matter of finding the sweet spot where enough air is still feeding the secondaries with primary air keeping the glass clean and feeding the base of the fire. At that point, usually the flames get lazy for a bit until the secondaries take over. Where the air control is set to achieve this depends on the draft. If the flue is drawing well, often it is with the air control shut off as far as it can go.

 

[SmokeyCity]

I can't speak for all non cats but I have the Englander 30 and you cannot sustain such a burn indefinitely as you can with the CAT. The CAT is simply more effective at lowering the flashpoint of the smoke down to arounf 550 ish. The non cats require temperatures of almost twice that to flash the smoke.

I have gotten those steel tubes glowing cherry red and been able to burn very hot and clean at a low air intake volume for extended times - but once I choke it all the way wdown to a smolder - the non cat just can;t sustain combustion of the smoke for long - it needs too much of its own heat to maintain temperature and thus can't self sustain w/out more air to produce more heat which requires burning the wood faster.

CAT can burn the wood slower and more efficiently by requiring less heat and less air to maintain ignition.

Again this is just my experience with the Englander 30 vs. all Ive *read* about the CATS. I don't own both types.

Whoever invented the CAT stove deserves a Nobel.

Maybe the CAT guys can sound off on this.

When you burn a non-cat stove with secondary air tubes, I gather that you need to get the firebox up to around 1000 degrees for the smoke to light-off.

When the secondaries light-off, is the heat from the secondaries enough heat maintain the heat necessary to keep the smoke burning?

If secondary burn heat is enough to keep the smoke burning, then can you shut down the damper (I assume primary and maybe secondary dampers) such that you have a smoldering fire with very little flame - totally relying on the secondary burn to maintain enough heat to burn the smoke from the smoldering wood. Does this work?

The reason I ask is because I have a catalyst combuster stove, Woodstock Keystone and it will burn the cat brightly on pretty much smoke alone with a few red embers and no flames for a clean low burn.

I also have an Englander 30 non-cat stove that will get installed this fall. If the above is correct, then one could get a smoldering low burn while maintaining the secondaries (until the wood goes to charcoal and no more outgassing) not unlike a cat stove. The only difference is you have to get the stove up to a higher temp on a non-cat to light-off the secondaries, but then relying on the secondaries to maintain the heat necessary to keep the burn going, turn down the damper and let the stove cruise for a clean, long burn. Instead of a glowing cat burning the smoke, the secondaries burn the smoke.

We talk a lot about shoulder season burns being very easy to do with a cat stove, but I'm thinking the same is possible with the non-cat secondary tube type stoves like my Englander.

Have I got this correct or am I way off base?

Thanks!
Bill

 

[shawneyboy]

All things are relative, including the stove design and materials. With my stone stove I can get the secondaries going very quickly, from a cold start, even when my stove top is quite cool. You need the air in the firebox to raise, not the stove surface itself. This being said, when a steel or cast stove fires off the secondaries the stove itself is much hotter than a stone stove. The secondaries can and will last a long time, on a full load, many hours.

Shawn

 

[gogreenburnwood]

Well I can't comment on non-cat until next season since I'm replacing my cat stove, DW small convection, with the PE Alderlea T5. My cat is surrounded by insulation, so even though it burns more efficiently the heat doesn't really make it to the house, because it is directed to go up the pipe. Yes it's true you can choke a cat stove down once the cat is engaged, but it takes a while for it to get up to temp, then if you don't feed more wood then you repeat the heating process to get it back above 500 degrees. I'm sure the non-cat has the same process, I'm just hoping it happens faster. If you want a hot fire you have to feed the cat with cooler air to keep it from overheating and shortening the ceramic's life (cracking and breakage). If you don't pay attention to that and leave it open too long, then the cooler air will drop it below 500 and you lose the efficiency. To be honest I'm looking forward to a stove that doesn't require so much fussing to operate it correctly, 1 air control and 1 door is in my future. Don't get me wrong my DW has served me well for the last 20 years, but the old stove is starting to go through cat's, 2 in the last 5 years, and a cat stove does not heat if the cat is not functioning believe me. The cool air "protection" tubes are degraded and broken allowing the flame to directly impact the ceramic, hence a new stove vs fixing internals.

 

[certified106]

All things are relative, including the stove design and materials. With my stone stove I can get the secondaries going very quickly, from a cold start, even when my stove top is quite cool. You need the air in the firebox to raise, not the stove surface itself. This being said, when a steel or cast stove fires off the secondaries the stove itself is much hotter than a stone stove. The secondaries can and will last a long time, on a full load, many hours.

Shawn

I was amazed at how quickly the secondaries lit off in my T6. At times my flue is temp is barely 200° on a start up an my secondaries are already going 10 minutes into it.

 

[leeave96]

I can see you are thinking cat technology for non-cat burning. In practice, it's quite different. The interior of the firebox may be reaching 750F, but the stove top could be only 400-500F and still support good secondary combustion. Assuming there is proper draft, once they get burning, if the wood is dry, the stove temp will rise a bit and the secondary burn will continue until the wood has stopped outgassing. However, a smoldering fire is not what you want. It is more a matter of finding the sweet spot where enough air is still feeding the secondaries with primary air keeping the glass clean and feeding the base of the fire. At that point, usually the flames get lazy for a bit until the secondaries take over. Where the air control is set to achieve this depends on the draft. If the flue is drawing well, often it is with the air control shut off as far as it can go.

I agree - you have to have enough air to allow combustion. I'm just guessing that those secondary gas burns, if enough air is present, to maintain them while the primary air is cut to near zero.

I'll find out when I get the Englander 30 installed.

I'm just courious about how this non-cat stove works before my install. Sort of like studying for an exam!

Thanks,
Bill

 

[Highbeam]

In my experience with our softer woods and a modern stone stove where the primary can only be shut so far, even at zero setting it still allows some air. That air mostlt runs down the airwash and is not enough to do anything but keep the glass clean. The fuel load can have no visible flames but the roof of the firebox is engulfed in secondary combustion. Almost all non-cat stoves have an uncontrolled secondary air supply, it's wide open. The secondary combustion event is so big and near the fuel load that it literally broils the fuel which causes more wood gas to be emitted to further the secondary combustion. This broiling action is why the secondaries are self sustaining. It is also why the secondary combustion can be rather huge and uncontrollable, causing runaway stoves when too much wood gas is broiled out at once.

Some of my hottest stove temps have occured when the only air control is set to zero. Doesn't that scare anybody? You generally expect a car to slow down when you take your foot off the gas.

Gogreenburnwood: Dennis will love you when he reads that yet another person finds cat stoves to be more complicated than non-cats. I agree, there are more steps including temps control but the rewards are huge. If only you had a better stove.

 

[leeave96]

In my experience with our softer woods and a modern stone stove where the primary can only be shut so far, even at zero setting it still allows some air. That air mostlt runs down the airwash and is not enough to do anything but keep the glass clean. The fuel load can have no visible flames but the roof of the firebox is engulfed in secondary combustion. Almost all non-cat stoves have an uncontrolled secondary air supply, it's wide open. The secondary combustion event is so big and near the fuel load that it literally broils the fuel which causes more wood gas to be emitted to further the secondary combustion. This broiling action is why the secondaries are self sustaining. It is also why the secondary combustion can be rather huge and uncontrollable, causing runaway stoves when too much wood gas is broiled out at once.

Some of my hottest stove temps have occured when the only air control is set to zero. Doesn't that scare anybody? You generally expect a car to slow down when you take your foot off the gas.

Gogreenburnwood: Dennis will love you when he reads that yet another person finds cat stoves to be more complicated than non-cats. I agree, there are more steps including temps control but the rewards are huge. If only you had a better stove.

I can't say that my cat Woodstock Keystone is complicated or more complicated to use. It's pretty much a no brainer. The current issue I have with my cat stove is the cat combustor has pretty much stopped working - see my separate thread on this. My expection of my cat stove and secondary tube burn stove is going to be the same - bring the stove up to temp, ignite the cat or secondaries, damper down. I does, however, cause me some concern that there is potential for a runaway burn in the non-cat stoves and from time to time we read about them on this forum - heck even Brother Bart had one this past season. I've never been close on my cat stove. Load it full, while the stove is 500 degrees stove top, damper down and off to bed for the night. I'll be a little more careful with the Englander 30 until I get use to it. When I read about these runaway non-cat stoves, it makes me think one needs a mod to the stove to have the option to cut-off all air to the stove if necessary - especially if, God forbid, there is a flue fire.

BTY, very nice stove you got with the Hearthstone.

Bill

 

[certified106]

In my experience with our softer woods and a modern stone stove where the primary can only be shut so far, even at zero setting it still allows some air. That air mostlt runs down the airwash and is not enough to do anything but keep the glass clean. The fuel load can have no visible flames but the roof of the firebox is engulfed in secondary combustion. Almost all non-cat stoves have an uncontrolled secondary air supply, it's wide open. The secondary combustion event is so big and near the fuel load that it literally broils the fuel which causes more wood gas to be emitted to further the secondary combustion. This broiling action is why the secondaries are self sustaining. It is also why the secondary combustion can be rather huge and uncontrollable, causing runaway stoves when too much wood gas is broiled out at once.

Some of my hottest stove temps have occured when the only air control is set to zero. Doesn't that scare anybody? You generally expect a car to slow down when you take your foot off the gas.

Gogreenburnwood: Dennis will love you when he reads that yet another person finds cat stoves to be more complicated than non-cats. I agree, there are more steps including temps control but the rewards are huge. If only you had a better stove.

Highbeam, Are you unhappy with your hearthstone? I have found in my limited experience that if I shut start shutting the stove down early and in a couple of stages that my secondary combustion was pretty controlled and stayed pretty mild mannered with almost almost no flames on the wood. On the other had if I really had it ripping for a period of time and then shut it down the secondary combustion stayed much hotter and burned the load down quite a bit quicker and hotter.

 

[Highbeam]

I am happy with my Hearthstone. It performs exactly as advertised and has never let me down. I can suggest some improvements of course but none related to performance.

The non-cat style of stove has a weakness in that you are only partially in control of the fire but that is usually okay. It's about expectations and trust. I know that the stove will continue to get hotter with the air shut off. I trust that it will not overheat and go nuclear based on experience. I can stuff it full, char the load, shut the air to zero and go to bed knowing full well that the stove won't explode. It will run up to 450-475 and then stay there. If I wanted it to go to 350 and stay there then I am out of luck, the non-cat style does not offer this level of control.

I've run over 20 cords through this stove. It is dependable.

 

[shawneyboy]

I am happy with my Hearthstone. It performs exactly as advertised and has never let me down. I can suggest some improvements of course but none related to performance.

The non-cat style of stove has a weakness in that you are only partially in control of the fire but that is usually okay. It's about expectations and trust. I know that the stove will continue to get hotter with the air shut off. I trust that it will not overheat and go nuclear based on experience. I can stuff it full, char the load, shut the air to zero and go to bed knowing full well that the stove won't explode. It will run up to 450-475 and then stay there. If I wanted it to go to 350 and stay there then I am out of luck, the non-cat style does not offer this level of control.

I've run over 20 cords through this stove. It is dependable.

Sounds like mine.... I love it. If I want to run at 350 or so I just adjust fuel load.

Shawn

 

[wkpoor]

Some of my hottest stove temps have occured when the only air control is set to zero. Doesn't that scare anybody? You generally expect a car to slow down when you take your foot off the gas.

Sure did and was one of the reasons I quit using the Magnolia. It would try to over fire itself quite often and I was stuffing smashed cans in the secondary inlet to slow it down.
I find my non-cat Elm to do a similar trick that can take it to as hot as 800 but it doesn't seem to limit burn times so I don't mind and the space I'm trying to heat so large its never is a problem. If I want to cool it off I can also just open the primary a little and it will come right down off the high temps.

 

[Loco Gringo]

This is why I started a thread a few weeks back asking if a cat stove could be operated if there was a problem with the combusor. Things break, go bad, and sometimes just cant be repaired or replaced because of certain circumstances, and Ive seen a lot of parts here that can go bad on the cat models. I didnt want something like that to be worried about. I like to keep it simple. Should we have a long term power outage, gas shortage limiting transportation, or some form of crisis whether its in my home or within the nation, I can and will burn wood to stay warm and cook our meals. Thats all I was after and I got it while burning a small fraction of what I was in the past. I just couldnt be much happier with the amount of wood I am now burning. And I sure as hell couldnt justify the additional price I would have paid compared to the results Im getting. If a man is happy with a catalytic burner thats great, but I couldnt justify paying the price I would have in order to get more than what I have now. Longer burn times and a cord less burned a year? I dont think so. Not in my situation anyway. Ill just split an hour more a year and maintain my fire in a timely and accurate manner.

 

[Loco Gringo]

Sorry double post

 

[grommal]

I can see you are thinking cat technology for non-cat burning. In practice, it's quite different. The interior of the firebox may be reaching 750F, but the stove top could be only 400-500F and still support good secondary combustion. Assuming there is proper draft, once they get burning, if the wood is dry, the stove temp will rise a bit and the secondary burn will continue until the wood has stopped outgassing. However, a smoldering fire is not what you want. It is more a matter of finding the sweet spot where enough air is still feeding the secondaries with primary air keeping the glass clean and feeding the base of the fire. At that point, usually the flames get lazy for a bit until the secondaries take over. Where the air control is set to achieve this depends on the draft. If the flue is drawing well, often it is with the air control shut off as far as it can go.

I agree - you have to have enough air to allow combustion. I'm just guessing that those secondary gas burns, if enough air is present, to maintain them while the primary air is cut to near zero.

I'll find out when I get the Englander 30 installed.

I'm just courious about how this non-cat stove works before my install. Sort of like studying for an exam!

Thanks,
Bill

The best answer is that you'll need to play with the stove a bit to learn how it wants to work. On a cold start, I can get good looking secondaries with stovetop only at 300F on my Oslo, maybe 20 minutes after putting match to the fire. But if I shut down the primary air all the way the instant I see secondaries on a cold start, they will stall. The key is to get the internal temperature of the firebox hot enough so that the secondary air is preheated enough to sustain things. With a little practice, you'll learn exactly where that is on the new stove. With my Oslo, I crank the primary air down to half when secondaries appear, and then wait about 10 more minutes (with secondaries getting stronger) and shut down the primary as far as it will go. On a warm restart, I don't need as long a delay. On a hot reload, no delay.

It will also depend on the wood. The dryer the wood, the easier it is to get the gases inside the firebox to ignite. Higher moisture will require higher internal firebox temperature in order to maintain good secondaries.

 

[certified106]

I am happy with my Hearthstone. It performs exactly as advertised and has never let me down. I can suggest some improvements of course but none related to performance.

The non-cat style of stove has a weakness in that you are only partially in control of the fire but that is usually okay. It's about expectations and trust. I know that the stove will continue to get hotter with the air shut off. I trust that it will not overheat and go nuclear based on experience. I can stuff it full, char the load, shut the air to zero and go to bed knowing full well that the stove won't explode. It will run up to 450-475 and then stay there. If I wanted it to go to 350 and stay there then I am out of luck, the non-cat style does not offer this level of control.

I've run over 20 cords through this stove. It is dependable.

I understand what your saying. I guess the only model that truly mimics a cat stove to an extent is the T5 which adjusts the secondary as well as the primary. If my house had been a little smaller that is the stove I would have right now. For me though the only time I am worried about an overshoot in temp in the house is if I'm sitting right there in the living room and if I'm right there I just don't stuff it full. I can't wait to try the stove I have out in the colder weather though as my last stove lacked a little bit on the top end when it was cold.

 

[gogreenburnwood]

OK no you all have me wondering. With all this talk about not controlling the secondary air and the chance of continuing to feed a chimney fire I'm a little concerned. Certified106 you say the T5 single control lever controls both primary and secondary? Does anyone have a picture or document that shows that? I have on occasion over the last 25 years or so of burning in my dutchwest left the bypass damper open and gotten distracted, only to be alerted by smell or stovepipe noises that I was on the verge of a chimney fire. Closing the bypass and shutting the air has ALWAYS stopped it. Now you're telling me I may not have that control! I know that my new stove will have totally new operating characteristics, and I will learn them as I go. I am not going to let this uncontrollable secondary air thing bother me. I have a long time till next season to start using my new stove and will not let my excitement about the $2500 purchase get tarnished by this.

 

[HollowHill]

In my experience with our softer woods and a modern stone stove where the primary can only be shut so far, even at zero setting it still allows some air. That air mostlt runs down the airwash and is not enough to do anything but keep the glass clean. The fuel load can have no visible flames but the roof of the firebox is engulfed in secondary combustion. Almost all non-cat stoves have an uncontrolled secondary air supply, it's wide open. The secondary combustion event is so big and near the fuel load that it literally broils the fuel which causes more wood gas to be emitted to further the secondary combustion. This broiling action is why the secondaries are self sustaining. It is also why the secondary combustion can be rather huge and uncontrollable, causing runaway stoves when too much wood gas is broiled out at once.

Some of my hottest stove temps have occured when the only air control is set to zero. Doesn't that scare anybody? You generally expect a car to slow down when you take your foot off the gas.

This thread concerned me, new to burning, and worried about just such a situation. I'm planning on getting the new hybrid Woodstock stove, which has both cat and secondary combustion. I called them to ask about the controllability of the secondary combustion in their new stove and they are working on having one control that will control both the primary and secondary air. This should provide for a more controllable secondary burn, correct?

 

[certified106]

The easiest reply to all of these chimney fire questions is to just burn good wood and burn it properly. A chimney fire has to have fuel to burn and if there is no creosote in your chimney then you can't have a fire end of story. If you are burning green or less than desirable wood you will be running your cat stove in bypass mode a lot which has just as much chance of creating a chimney fire. My best friend at work burns a regency secondary combustion stove with well seasoned wood and he hasn't cleaned his chimney in 5 years. I have seen the chimney and it looks great. Just burn good wood and if you are worried about your wood check and clean your chimney often during the year until you are comfortable with how your stove is burning and that advice is for a cat or non cat stove. Now everyone needs to go get three years ahead on their firewood hahaha

 

[grommal]

OK no you all have me wondering. With all this talk about not controlling the secondary air and the chance of continuing to feed a chimney fire I'm a little concerned. Certified106 you say the T5 single control lever controls both primary and secondary? Does anyone have a picture or document that shows that? I have on occasion over the last 25 years or so of burning in my dutchwest left the bypass damper open and gotten distracted, only to be alerted by smell or stovepipe noises that I was on the verge of a chimney fire. Closing the bypass and shutting the air has ALWAYS stopped it. Now you're telling me I may not have that control! I know that my new stove will have totally new operating characteristics, and I will learn them as I go. I am not going to let this uncontrollable secondary air thing bother me. I have a long time till next season to start using my new stove and will not let my excitement about the $2500 purchase get tarnished by this.

My old VC cat had a secondary air system to feed air into the cat chamber, and this air inlet was not user-controllable. Not sure if other cat stoves have this, but if they do, then it's basically the same situation cat or non-cat.

I don't think the total airflow you could get through the little holes in the secondary tubes would be enough to really keep a chimney fire roaring. Might snuff it out a little more slowly than if you could shut off all the air tight, but I'm not sure the difference would be much. In the case of my current stove, a non-cat Oslo, all the air enters through a round hole on the bottom of the stove, then splits to primary and secondary from there. I could cover that hole quite easily if I ever had a chimney fire.

I used to get the hot stovepipe on my VC if I ran with the cat bypass open too long, too. With the Oslo, that basically doesn't happen unless I leave a door open, which I never do, even at startup. Even so, just because the stovepipe gets hot enough to smell the paint does not mean you're getting close to a chimney fire. A chimney fire needs fuel in the chimney, so if your chimney is clean, you're ok.

 

[HollowHill]

OK, I'm confused (it takes so little). I thought we were talking about runaway stoves (stoves getting to too high temps due to the inability to control the secondary combustion). Chimney fires are different, aren't they, in that they happen in the chimney, not the stove? I feel like I'm missing something here, forgive my ignorance.

 

[certified106]

OK, I'm confused (it takes so little). I thought we were talking about runaway stoves (stoves getting to too high temps due to the inability to control the secondary combustion). Chimney fires are different, aren't they, in that they happen in the chimney, not the stove? I feel like I'm missing something here, forgive my ignorance.

You are correct, they were talking about runaway stoves which turned in to talking about chimney fires. I just wanted to clear up the fact that chimney fires can only occur with fuel in the chimney and then Grommal made a great point and cleared it up a little bit more when he stated there is a difference between a hot chimney and a chimney fire. Now back to discussing runaway stoves....Who has actually had one run away?

 

[Highbeam]

The T5 series stove from PE is the only stove I know of that offers some level of control over the secondary air system. The rest are wide open all the time in an effort to always provide an oxygen rich environment and encourage the afterburn of smoke which would reduce emissions. There are no more "air tight" stoves. You can not snuff out a fire and this is by design because a snuffed fire is a smokey fire and emissions would go up.

The T5 uses a super secret mechanism to simultaneously close the primary and secondary air inlets with a single lever. There is some effort made to conceal this secret for some reason. I can assure you that the secondary air inlet, or the primary inlet, is never totally closed. This stove is the closest thing you can get to a cat stove in performance.

On some stoves, like my Hearthstone, all combustion air comes through a single air intake port which is conveniently the shape of a 3" pipe to allow outside air to be ducted and supply 100% of combustion air. Also allows me to block it off if I ever need to. The rest of the stoves have sneaky secondary inlet(s) that can be hard to find and harder to throttle.