Secondary combustion in a soapstone stove without any technology?

[adamscotera]

I have a Woodstock Fireview. The company says that in general, you can expect the surface temperature to be about half the internal temperature. I assume this mainly applies when the stove is thoroughly hot and a fairly steady burn is underway. The information I can find about secondary combustion of woodsmoke indicates that it burns at about 1100 degrees F. This leads me to speculate that if I am running a soapstone stove at a surface temp of 550, I should expect that secondary combustion of the smoke is happening in the firebox regardless of any technology the stove may or may not have. About a week of using my stove without the combustor (it's plugged with ash and perhaps some creosote due apparently to excessive moisture in my wood) has produced the following observations:
1. When the surface temp is 500 (actually anything above 425), I see and smell no smoke unless I've just put wood in.
2. I can't seem to get the stove any hotter than 600 (although maybe with some properly dry wood I could).
3. It burns long and slow at 500+ for as long as the fuel holds out, an hour or so per small log.
I'm definitely not losing 40-50% of my heat potential up the chimney. If anything, it's heating better. I think the majority of the smoke is being burned before exiting the firebox. This, I think, is what experienced users of old iron stoves do to burn cleanly and efficiently, but soapstone makes it easier because the outside of the stove doesn't need to be as hot and the temp in the firebox doesn't change as quickly over time, also the cool spots are not as cool. Has anyone done any testing with a probe thermometer to see what exactly are the temperatures in a soapstone firebox over the course of a medium burn?

 

[swestall]

Sounds like you are getting it right and don't know it. You should not really get the stove much hotter than 600. 450-550 is good depending on what you are looking to get to. ON those -10 to 25 degree days you might want to go hotter but your 500 is most likely what the CAT is bumping the temp up to.
If you are worried about the internal temp (why?) use an infared thermometer and check it yourself.
As long as you see no smoke out the stack you are doing it.
The stone is going to absorb then dissapate the heat. I imagine its doing that, right?
Sit back and enjoy your heat and the movie in the stove.

 

[HotCoals]

He's saying he does not have the cat in it and was wondering how much secondary burn was happening anyways..and that he thought it might even be doing better without it.
I think he likes the stove just fine but would like dryer wood..that's what I got out of it.
Sounds reasonable.

 

[Huntindog1]

How long of burn time are you getting with the stove burning at 550?

With green wood thats keeping your from reaching over 600 , I would expect to see some smoke out the flue. How tall is your flue? As the longer the flue is the more time it has to cool.

 

[Woody Stover]

using my stove without the combustor (it's plugged with ash and perhaps some creosote due apparently to excessive moisture in my wood

How are you running the stove? Combustor removed? Bypass open or closed?

 

[Todd]

I think Woodstock is saying the cat temps are roughly double the external temps not the internal fire box temps. Never tried it without the cat but I bet the internal temps will be much cooler. The cat also somewhat acts as an internal damper that slows down the draft and keeps more heat in the stove. You may see some secondary combustion without the cat because of the baffle and the holes in the air wash plate but I don't think it's going to be very efficient.

Are you monitoring your pipe temps? I bet they are much higher without the cat and your losing heat up the stack. Even if your wood is not that dry I'd still burn with the cat in there, it will be more efficient and give you more heat. You can get by with less than dry wood in this stove by splitting your wood smaller, burn in the bypass a little longer and using more air. Also check the cat a little more often to keep it from plugging.

 

[Backwoods Savage]

I have a Woodstock Fireview. The company says that in general, you can expect the surface temperature to be about half the internal temperature. I assume this mainly applies when the stove is thoroughly hot and a fairly steady burn is underway. The information I can find about secondary combustion of woodsmoke indicates that it burns at about 1100 degrees F. This leads me to speculate that if I am running a soapstone stove at a surface temp of 550, I should expect that secondary combustion of the smoke is happening in the firebox regardless of any technology the stove may or may not have. About a week of using my stove without the combustor (it's plugged with ash and perhaps some creosote due apparently to excessive moisture in my wood) has produced the following observations:
1. When the surface temp is 500 (actually anything above 425), I see and smell no smoke unless I've just put wood in.
2. I can't seem to get the stove any hotter than 600 (although maybe with some properly dry wood I could).
3. It burns long and slow at 500+ for as long as the fuel holds out, an hour or so per small log.
I'm definitely not losing 40-50% of my heat potential up the chimney. If anything, it's heating better. I think the majority of the smoke is being burned before exiting the firebox. This, I think, is what experienced users of old iron stoves do to burn cleanly and efficiently, but soapstone makes it easier because the outside of the stove doesn't need to be as hot and the temp in the firebox doesn't change as quickly over time, also the cool spots are not as cool. Has anyone done any testing with a probe thermometer to see what exactly are the temperatures in a soapstone firebox over the course of a medium burn?

The surface temperature they are referring to is at the top of the stove and not in the firebox. With the temperatures you are getting, I'm guessing you have pulled the cat out and leaving the bypass closed. For sure if it is open you are losing lots and lots of heat. With the combuster plugged, this tells what your problem is and it is the fuel. Until you fix that problem you will have problems with any stove.

As for seeing smoke, you are probably seeing it a lot longer than you did with the cat in.

Can't get over 600 degrees? I would expect that with poor fuel and no catalyst. You say it burns long and slow. What is the definition of that?

How can you know that you are not losing 40-50% of the heat up the chimney? With the cat not slowing down the burn, the smoke and gasses have easy access to the flue so it is normal that they would flow faster and thereby lose heat up the chimney. What are your flue temperatures like? For reference, ours generally run 300-350 in the flue.

It would be interesting if you had an IR temperature gun. I have no doubt you will find the sides of the stove are not nearly has hot as when you have the cat installed. I would also be interested in how you are running the draft setting. As for a probe in the firebox, why? A probe near the cat would give you better information. An IR gun will help a lot with this too.

 

[Backwoods Savage]

Sounds like you are getting it right and don't know it. You should not really get the stove much hotter than 600. 450-550 is good depending on what you are looking to get to. ON those -10 to 25 degree days you might want to go hotter but your 500 is most likely what the CAT is bumping the temp up to.
If you are worried about the internal temp (why?) use an infared thermometer and check it yourself.
As long as you see no smoke out the stack you are doing it.
The stone is going to absorb then dissapate the heat. I imagine its doing that, right?
Sit back and enjoy your heat and the movie in the stove.

There is no good reason to not get this stove over 600 and we regularly get the stove over 650 degrees. The Woodstock and Heartstone are two different stoves so just like a Woodstock owner should not tell a Hearthstone owner to burn over 600, the same goes the other way around. Hearthstone recommends 600 as tops and Woodstock recommends 700 as tops. We have had our stove to 700 a few times with no problems except a bit more heat than we intended at the time.

 

[Stump_Branch]

[quote author="Backwoods Savage"/]

We have had our stove to 700 a few times with no problems except a bit more heat than we intended at the time.[/quote]

+ 1 the truth.

 

[Martin Strand III]

My thoughts.

Your problem is essentially not seeing the forest because of the trees.

Expecting the soapstone in the stove to compensate for your errors
(not dry wood, clogged cat converter) is unrealistic.

Instead of worrying about high tech IR thermometers to find out
firebox temperatures, start with the basics and correct your
mistakes first.

Imagine why your new sports car doesn't rev up and run with
the big dogs if you put water contaminated gas in the tank.

Good grief man, learn to walk before you run.

Aye,
Marty

 

[swestall]

Sounds like you are getting it right and don't know it. You should not really get the stove much hotter than 600. 450-550 is good depending on what you are looking to get to. ON those -10 to 25 degree days you might want to go hotter but your 500 is most likely what the CAT is bumping the temp up to.
If you are worried about the internal temp (why?) use an infared thermometer and check it yourself.
As long as you see no smoke out the stack you are doing it.
The stone is going to absorb then dissapate the heat. I imagine its doing that, right?
Sit back and enjoy your heat and the movie in the stove.

There is no good reason to not get this stove over 600 and we regularly get the stove over 650 degrees. The Woodstock and Heartstone are two different stoves so just like a Woodstock owner should not tell a Hearthstone owner to burn over 600, the same goes the other way around. Hearthstone recommends 600 as tops and Woodstock recommends 700 as tops. We have had our stove to 700 a few times with no problems except a bit more heat than we intended at the time.

I had a discussion with some folks at Hearthstone a few years ago and they indicated you could get their stoves up to 700 without causing a big problem. The 600 they publish is what they do not want you to exceed. I know you can run the Woodstocks up there too. But, I really don't think one should be looking to run them that hot or think if they are not there is a big problem. When I am running 550 the stove is cruising along with great secondary combustion and a lot of heat in the house. It uses the wood much faster though and that is my problem with it. When we get into the low 20's to -10's then I'm burning above 450-500; other than that I try to keep it at 450 more or less so as to get the best use of my wood. Wood is expensive in labor,money and time.
I do concede that I've not burned a Woodstock; almost got one but decided to go with the Hearthstone instead. I love them both.
I also agree with the fuel issues. A couple years ago I had to burn some that was only 1.5 years seasoned and it had a higher moisture content. That did cause me to burn "more difficultly". I had to keep more air in the feed and it did not get blazing for much longer a time. When I installed the in line damper just above the stove outlet that helped with my burns a lot. I am leaving the inlet open a bit more and restricting the outflow more: the secondaries love that and therefore the heat output is far better.

Best O' the Burn to all!!

 

[adamscotera]

Hi All,
Thanks for the input. To clarify: I'm not concerned about trying to get the stove over 600. It will cruise along fine at 500-550 with wood that is a little too moist, and that's cool. If I do get a few dry logs at once, which happened the other day, it can get up to 700 or so. About the quality of my fuel- it's only my second season. I don't have control of the wood yet, as I've bought "seasoned" wood both years, but now I understand what one of the posters meant when he said that you should keep your "seasoned" wood a year before you burn it.
I disagree that the combustor keeps more heat inside the firebox. I can tell you that this stove is putting out more heat now (without the combustor) when the top thermometer reads 550 than it did with the combustor when the top read 650. It feels warmer, and the temperatures in different parts of the house are higher. Overnight burns are at least as successful as they were with the combustor in. What I will say in defense of the combustor is that there is definitely more smoke after loading, and there was soot on the inside walls of the stove after a slow, all-night burn, whereas there wasn't any soot when I did that with the combustor in. (Because of this, I plan to avoid long, slow burns unless I am using a catalyst.)
BUT The problem is that I know how to run this stove, and I found a way to stabilize the firebox temperature so the fire wouldn't go out even though the wood wasn't great, and I made sure that catalytic burn temperatures were maintained at all times, and still the combustor failed due to clogging about a week after the last time I had cleaned it. (I have cleaned it 2 or 3 times since October.) I had no choice but to conclude that you cannot run this stove with the combustor unless your wood is better than mine. So that's why I'm not using the combustor. I may use it next season if I think my wood is better. Or I might just take all the iron out of it and use it the way it was originally designed- as a top loader. I'll keep you all posted if you want.
Adam

 

[Huntindog1]

The reason that the stove wasnt heating up as well with the combustor in was that the combustor is limting the air flow as the stove was designed to burn at low air as the combustor will generate more heat if its working. So sounds like your combustor wasnt working , maybe its bad, or its the wet wood. If your wood is wet you may not have been able to keep the combustor in the operation temperature range.

But in a sense you are right the stove wasnt designed to burn wet wood. As the moisture comes out of the wood its travels up into the combustor and cools it, out of its operating temperature range. Its like you standing there with the door open with a spray bottle of water , spraying it into the fire box. The stove really wasnt designed to burn the wood as much as it was designed to burn the smoke. Your not getting the heat out of it as your not getting any heat from the combustor and thus your trying to get heat out of just burning wood and the stoves air is limited to be a smoke burner. Once you took out the combustor your air flow is greatly increased but your only going to be able to burn at air burn rates or the stove will be creating creosote if you damper it down too much.

 

[Todd]

I wouldn't take the baffle out and burn it as a top loader. The baffle probably helps hold the whole stove together and also slows down and directs the smoke and gas up through the combustor. Removing it would just send all the heat right out the back. I'm pretty sure once you have good wood your results will be much better with the combustor installed. A lot of R&D went into this stove, I'd burn it as Woodstock intended it to be burned. You may even want to call them and discuss this, they may decide you need a new cat and send you a free one.

What are your pipe temps at burning without the cat?

 

[jdonna]

I had torn my fireview completely apart. With echoing what Todd stated, if you modify the top cast iron piece you are compromising the integrity of the stove. Also the top stone lid would be subjected to much higher temperatures because of direct flame contact. Draft would be increased a lot as well, would be similar to running it in bypass mode with a direct flame path into your flue.

I am guessing it would take a very long time to cut through the duct cover, that baby is seriously thick!

I suggest you get yourself a stainless steel cat and find some good wood to run through it and you will love it.

At the end of the day though, it is your stove and you can do as you wish with it. Just be safe!

 

[Backwoods Savage]

Sounds like you are getting it right and don't know it. You should not really get the stove much hotter than 600. 450-550 is good depending on what you are looking to get to. ON those -10 to 25 degree days you might want to go hotter but your 500 is most likely what the CAT is bumping the temp up to.
If you are worried about the internal temp (why?) use an infared thermometer and check it yourself.
As long as you see no smoke out the stack you are doing it.
The stone is going to absorb then dissapate the heat. I imagine its doing that, right?
Sit back and enjoy your heat and the movie in the stove.

There is no good reason to not get this stove over 600 and we regularly get the stove over 650 degrees. The Woodstock and Heartstone are two different stoves so just like a Woodstock owner should not tell a Hearthstone owner to burn over 600, the same goes the other way around. Hearthstone recommends 600 as tops and Woodstock recommends 700 as tops. We have had our stove to 700 a few times with no problems except a bit more heat than we intended at the time.

I had a discussion with some folks at Hearthstone a few years ago and they indicated you could get their stoves up to 700 without causing a big problem. The 600 they publish is what they do not want you to exceed. I know you can run the Woodstocks up there too. But, I really don't think one should be looking to run them that hot or think if they are not there is a big problem. When I am running 550 the stove is cruising along with great secondary combustion and a lot of heat in the house. It uses the wood much faster though and that is my problem with it. When we get into the low 20's to -10's then I'm burning above 450-500; other than that I try to keep it at 450 more or less so as to get the best use of my wood. Wood is expensive in labor,money and time.
I do concede that I've not burned a Woodstock; almost got one but decided to go with the Hearthstone instead. I love them both.
I also agree with the fuel issues. A couple years ago I had to burn some that was only 1.5 years seasoned and it had a higher moisture content. That did cause me to burn "more difficultly". I had to keep more air in the feed and it did not get blazing for much longer a time. When I installed the in line damper just above the stove outlet that helped with my burns a lot. I am leaving the inlet open a bit more and restricting the outflow more: the secondaries love that and therefore the heat output is far better.

Best O' the Burn to all!!

I understand where you are coming from and I can also state I know someone who had their Woodstock stove well over 800 degrees! For sure that would have scared the wits out of me and I certainly would not recommend it but for sure you can usually take a stove a bit above the manufacturers recommendations and hopefully not do any harm. I'm not so sure I'd be too happy with a stove I could not get over 600 when the outdoor temperature gets down below that zero mark!

 

[adamscotera]

Thanks again for all your ideas.
I am pretty sure I'm going to try burning wood in this stove with the air duct and combustor pan removed. There are clear instructions on Woodstock's website for how to remove those items. The stove is held together by long bolts that go into the legs. Also, at first when I started running without the combustor, I kept the bypass damper closed so as to direct the heat under the lid, but (because the wood is too damp) the back of the stove sometimes would cool off and I'd need to open the damper again to direct the flames back there. Then I started leaving the damper in a neutral position so the smoke can escape in both directions, and I haven't had that problem. As for the lid getting too hot, the flame in the firebox will not often reach the temperatures that the combustor generally produces when the wood is properly dry, so I don't worry about that. I think without any baffling, the heat will be distributed pretty well, and as long as I keep the firebox hot, the stove will burn pretty clean. What I will gain is about 30% more capacity in the firebox, which I hope will allow me to better heat my house with this stove. I will have to forgo the long slow burn, but I don't think I will miss it because between the heat storage of the stone and the basement itself, even if the fire is out by 3 or 4 am, the house will not have started to cool off much by the time I get up. And experience has shown that this stove will hold hot coals for hours even with the damper fairly open.
None of this should be taken to indicate that I think the combustor is worthless. Without it, there is no way to execute a clean and slow burn. The problems are 1) that it won't work if the wood isn't dry enough, and 2) that it seems to put a cap on the max heat output I can get, a cap that is just a little too low for me. As I said before, when the top thermometer says 650 with the combustor, I get heat output similar to when it says 500 or 550 without. I theorize that this is because with the combustor, the firebox is cooler than the space above the combustor, so the heat is disproportionately radiating from the top surface rather than the whole stove.
It may be that the stove will not function as well without the iron assemblies in the top. I'll find out, and post what I learn. The other advantage I'm hoping for is top loading. I'm sick of that little door! And embers falling out sometimes!
Adam

 

[Rhone]

I'm just going to say, the reason it's hard to get secondary burn in a non-secondary burn stove is that there's no oxygen left to burn the secondary gasses. The way secondary burn works is, there's typically tubes with holes (sometimes a plate w/holes) at the top that shoots fresh oxygen giving the secondary gasses oxygen up top to ignite. Next, it has to be very hot up there and comes the next element there's a piece of insulation above the secondary burn chamber which ensures it stays extremely hot, typically the tubes/secondary burn area is glowing cherry red. Now, you have the temps, the gasses, and oxygen for it to burn. But, you also have to have flames reaching it as secondary burn is not self sustaining. It stays lit for perhaps up to a minute or two without flames but it will die out without flames reaching it. All those 4 things, and you'll have secondary burn.

One of the gripes I've run into many times with a secondary burn stove is trying to keep flames reaching it so it stays ignited. I can't tell you how many times I've set the fire up, it's going great with secondary burn, and then it collapses on itself and no flames reach the tubes to keep it lit and it goes out... with the occasional flame lighting it now and then in a burst. When I came home, and my house heated 3-4F from a full fire I knew I lost the secondary burn. 6-10F was typical. To avoid that, for years I've placed a metal tube in the middle of my splits so even if it collapses there's always room for flames of the fire to tickle the secondary burn and keep it lit. No more 3-4F fires. The reason I mention this tube is, it rarely glows red which means the area directly above the splits is not typically hot enough for secondary burn. Often the secondary burn chamber of mine will be glowing cherry red while that pipe doesn't look to be glowing at all. So, although you will have some natural secondary burn going it's not significant... and if you keep your air open to max you'll get more of it happening inside the fire but then the heat will too quickly fly out your flue instead of transfer into the living area.

So, although you will have some secondary burn happening naturally in a non-secondary burn stove, it can't be anything close to the real deal except with the cat engaged. I also can't explain how you get more heat without using the catalytic converter. Here's a picture of secondary burn, and I'm just going to say that guy turned the air way down extinguishing the flames and only the secondary burn is happening for this picture... but you have to have flames from the splits tickling the secondary burn chamber. If this guy keeps it down like that for more than a minute or two it's going to go out. What I do like about it is, it demonstrates the effect of adding air so the secondary gasses have oxygen to burn, and you can see the effect it's burning around every hole.
(broken image removed)

 

[Todd]

Well, it's your stove so do what you want. How are you going to regulate the intake air? If you take out all the guts the air intake will be up high in the back under the rear exhaust where the air duct used to be. I think you would need a new door similar to the Woodstock Cassic so the combustion air is fed down low into the fire otherwise you will just have a smouldering mess.

Another thing you will find out is it won't be a top loader. That top lid is too big and without a rear bypass you will get a face full of smoke when you open it up.

 

[Martin Strand III]

Grandma used to say,
"Play with fire and you'll get burned."

Aye,
Marty

 

[adamscotera]

Hi Todd,
You've mentioned the two biggest concerns I have: intake air distribution and smoke release when opening the lid. Now, I was tentatively figuring that as long as the fire wasn't raging, but the stove was hot, the flue would suck all the smoke out. I have a pretty powerful draft and haven't ever gotten any smoke in the room when I've opened the lid before, with or without the combustor in place, but I have been trying to find some more information about the design of top loaders to see whether they have some sort of baffle or smoke guide to guard against this. And without the air guide in the Fireview, obviously the dynamics would be very different as the air would be coming down the back in two columns instead of a thin wash down the front.
Without endorsing the idea of taking the guts out of my stove, do you know of anywhere online where I can find information about how intake air and smoke exit are configured in some top loaders? (Or information about what Woodstock used to do in the pre-cat days?) I understand your advice is not to do it, and just to get ahold of some dry wood as soon as possible, which is certainly sound advice. Can't get any better wood this season though, and I still need to heat my house.
Thanks again,
Adam

 

[adamscotera]

Rhonemas,
Thanks for the pic, and the feedback about working with secondary combustion. I'd guess that "secondary combustion" may not be exactly the right term for what goes on in a pre-EPA stove that's burning clean. I guess it's more like mostly complete primary combustion instead. I think the key to getting a clean burn that way without losing too much heat is figuring out how to keep the flue temp under control while the stove is really hot. But you're right, burning the gases in the top of the stove definitely requires a second source of oxygen.

 

[Todd]

Hi Todd,
You've mentioned the two biggest concerns I have: intake air distribution and smoke release when opening the lid. Now, I was tentatively figuring that as long as the fire wasn't raging, but the stove was hot, the flue would suck all the smoke out. I have a pretty powerful draft and haven't ever gotten any smoke in the room when I've opened the lid before, with or without the combustor in place, but I have been trying to find some more information about the design of top loaders to see whether they have some sort of baffle or smoke guide to guard against this. And without the air guide in the Fireview, obviously the dynamics would be very different as the air would be coming down the back in two columns instead of a thin wash down the front.
Without endorsing the idea of taking the guts out of my stove, do you know of anywhere online where I can find information about how intake air and smoke exit are configured in some top loaders? (Or information about what Woodstock used to do in the pre-cat days?) I understand your advice is not to do it, and just to get ahold of some dry wood as soon as possible, which is certainly sound advice. Can't get any better wood this season though, and I still need to heat my house.
Thanks again,
Adam

As far as I know all the top loading stoves have a bypass so the smoke gets sucked out the back and out the rear of the stove so you can open the top front loading door. After loading you close the lid and close the bypass to get that secondary or cat burn going again. I just don't see how the top loading will work in the Fireview, they installed that lid for easy access to the cat and I believe the old non cats were designed with a solid top. The combustion air came through slots on the lower part of the side loading door. If you look at the Woodstock Classic or find a picture of the older Fireview mod 201 you can kind a figure out how the older non cats were designed then later incorporated a baffle system and cat.

Have you tried splitting your wood into smaller 2-3" splits to see if they would burn better? Maybe bring some inside next to the stove to help dry it out? Do you know anyone that has an over abundance of dry wood that may be willing to trade you for some of your wet wood? What about mixing in some dry pallet wood? You can usually find pallets for free. I know it's got to be frustrating, many here have been in your shoes before but we do what we can to get by. I'd hate to see you ruin your stove over this.

 

[adamscotera]

Todd,
Thanks for the conversation. Tonight I went down to do the deed, and as I was studying the stove, decided that it was unlikely to function well the way the intake air would be flowing (as you suggested). I did take out the scoop, which is not in great shape and which I plan to replace with the newer stainless steel one anyway. I also think you're right that the way it's set up, top loading won't work. I checked out the diagram of a Harman top loader, and saw that the smoke exits low in the back. However, I didn't come up with the idea that the Fireview used to be a top loader out of thin air- I had a stove builder from Woodstock here last year and he told me so. There was one post I found from 2010 by someone whose friend had an old non-cat Fireview, but I haven't been able to find any other references to it online. In the meantime, I'm certainly going to expend some effort this year on getting some 2-year seasoned wood, even if it's expensive, and hold a year's worth of other wood in reserve so I can get ahead of it. I'll give the combustor another shot then. I just wish I could get more heat out of this stove. It could be that I'll need a bigger stove (but the wife will HATE that idea...)
Adam

 

[Todd]

I'd really like to see some pictures of the older non cat Woodstock's if you ever come across any. There are a few pictures on their site of an old antique 1880's soapstone stove they refurbished that looks like it would still be a great heater. You should get a hold of that stove builder and pick his brain a little more.