cat combustor questions

[jpl1nh]

I bought my Woodstock Keystone used. Owner said it was four years old. She claims she damaged the combustor the first time she removed it for cleaning, and bought a new one near the end of the first year. That would make it 3 years old. When I got the stove and removed the ash shield on the firebox side (upstream side) the space between the ash shield and the combustor was so packed with ash that I had to brush of a good half inch to even see the surface of the combustor. Obviously there was no flow going through it for a while with all the ash there. I cleaned it off with a paint brush and a vacum and you are able to see right thru it now. I just replaced the bypass door which was warped. Woodstock suggested that might be due to the previous owner trying to engage the combustor and the air being unable to pass through so it forced its way out under the bypass door. The previous owner showed me how she cleaned the combustor which was to remove the stove pipe and clean the stack side (downstream side) with a vacum cleaner. The most important cleaning, I understand is actually the upstream side which I don't think she ever did from what she showed me and what I described above. With all that in mind, I figure the combustor has the equivelant of 2 to 3 years of use on it and should still be good. When I get the stove top up to 250 and engage it, it obviously fires up since the stack temp starts to drop and the stove top temp climbs to 450 or 500. I can also often see it glowing. However, I still have a small amount of grayish smoke coming out my chimney and when the combustor is glowing, only one side of it seems to glow, I don't think I've ever seen the other half glow. The combustor is rectangular and I'm wondering if its possible that one side of it is no longer functioning correctly. Its completely clean , there is no visible damage to it from shock or overfiring. All seals are tight on the bypass, everything else looks good. What do you think?

 

[n6crv]

Hello, because it is rectangular is it possible to turn it around? That way you will be able to see if the side that is not burning now starts. Just a thought.
Don

 

[jpl1nh]

Hello, because it is rectangular is it possible to turn it around? That way you will be able to see if the side that is not burning now starts. Just a thought.
Don

Great suggestion! I might be able to though the combustor holder is intended to sit in the frame just one way with a tab you grab to remove the whole assembly for cleaning etc. If turning that whole holder around doesn't work, I would need to remove the combustor from its frame to turn it around and would be concerned that I would damage it.

 

[cbrodsky]

Don't try to remove it from the frame - it may fall apart. Once these are burned once, they should stay in the metal frame to preserve the seal.

You might want to try letting the initial fire get a little hotter before engaging the cat to see if it makes a difference.

I bet you got a great deal if the previous user never read the manual to use it correctly - I can't believe someone would run it that way. BTW, Woodstock has posted on here before to say that you don't need to leave the bolts in the catalyst frame - this makes it even easier to remove for a quick cleaning on both sides.

-Colin

 

[cbrodsky]

ps - when running correctly at temp, you shouldn't see any smoke at all. You should just see heat waves off the chimney.

 

[jpl1nh]

Okay. this is embarrasing. I was running it tonight and realized that the cat was glowing solidly all the way across. I was seeing the reflection of the glowing cat on the inside bottom of the heat/ash shield! I think also that while I have it hot enough to engage the cat, I'm still not running the stove very hot since its 50 out and even a small fire for a couple of hours gets the house up to 75. When its colder and I'm running the stove more the way its intended and firebox temps are hotter, I'll check smoke levels. I suspect that will resula tin an all around cleaner burn then.

 

[elkimmeg]

JP there can be a lag time where some smoke will still be present, till the cat combustor get up into full operation. Could be as much as 20 minutes.

what I saying it is not an instant flip of a switch.. I would say if it is red glowing all the way across that would be normal

 

[Todd]

I was told that the cat doesn't have to be glowing to be working. When it is glowing the temps are over 1000 degrees and there is alot of secondary combustion taking place. My cat won't glow or just have some glowing with smaller loads, but when I fill her up and get her hot she'll glow all the way across. Lots of trial and error figuring out a cat stove for the first time. Once it gets a little colder and your burning full loads 24/7 you will see a more consistant burn.

 

[jpl1nh]

Playing around with air intake a bit, I seemed to notice that damping the stove down too much, especially earlier in the burn seemed to yield more smoke. Thinking about it a bit, I speculated that it might be possible to overwhelm the combustor with too much smoke and that I might get a cleaner burn by providing more air and a bit more complete combustion in the firebox before the airstream hit the combustor. While this means running the stove a bit hotter, it seemed to eliminate the smoke. So, is it possible to overwhelm the combustor?

 

[Rhone]

Although I'm not an expert I believe cat stoves are supposed to be most efficient turned down. The faster the exhaust the less time it has to come into contact with the catalyst, so less of it is burned. I believe that's how it's suppposed to go. What color is the faint smoke coming out your chimney? If it's blue, you have unburned fuel, if white (and usually only during the beginning of a fire) it's steam, and normal as steam doesn't burn.

I have a secondary burn unit, but when I start up I get blue smoke coming out my chimney until the secondary burn starts going (about 10 minutes) in which case the blue smoke turns into white (which is water vapor). Shortly afterward (another 10 minutes) the white smoke vanishes from the exhaust (as it's all evaporated from the wood at this point) and from then on it's all just invisible waves. The more dry the wood, the faster the whole process as the water vapor keeps things cooler slowing things down.

 

[jpl1nh]

Although I'm not an expert I believe cat stoves are supposed to be most efficient turned down. The faster the exhaust the less time it has to come into contact with the catalyst, so less of it is burned. I believe that's how it's suppposed to go. What color is the faint smoke coming out your chimney? If it's blue, you have unburned fuel, if white (and usually only during the beginning of a fire) it's steam, and normal as steam doesn't burn.

I have a secondary burn unit, but when I start up I get blue smoke coming out my chimney until the secondary burn starts going (about 10 minutes) in which case the blue smoke turns into white (which is water vapor). Shortly afterward (another 10 minutes) the white smoke vanishes from the exhaust (as it's all evaporated from the wood at this point) and from then on it's all just invisible waves. The more dry the wood, the faster the whole process as the water vapor keeps things cooler slowing things down until its evaporated.

Its blue

 

[Todd]

Rohnemas has it right. Cat stove are most efficient on a low slow burn. The cat needs temp, turbulance, and time to burn properly. Too much air and the smoke will rip right through the cat and won't have time to ignight. I know when I have a full load and the cat is glowing full bore I can see that white smoke or steam coming out my chimney for awhile then it turns to heat waves. You might not be waiting long enough to engage the cat, make sure your stove top temp is 200-250 on start ups before engaging and wait 10-15 minutes on reloads.

 

[jpl1nh]

Rhonemas, I think your point about cat stoves working well when turned down is quite true. However, I just spoke with Woodstock who agreed that it is possible to go a bit too far with that if your goal is a really clean burn. :long: If I smolder the fire, it can produce more smoke than the combustor can completely burn. And at this time of year isince I just want to take the chill off the house, I don't really get a hot firebox, great bed of coals etc that this stove runs best on, so if I turn it down too low it just isn't working at optimum. Interesting. Also I'm burning a mix of hemlock, some poplar, some punky stuff with some small clean hardwood thrown in so the fuel tends to be more of smoke producing fuel as well. It's an ongoing learning experience it tis.

 

[jpl1nh]

Rohnemas has it right. Cat stove are most efficient on a low slow burn. The cat needs temp, turbulance, and time to burn properly. Too much air and the smoke will rip right through the cat and won't have time to ignight. I know when I have a full load and the cat is glowing full bore I can see that white smoke or steam coming out my chimney for awhile then it turns to heat waves. You might not be waiting long enough to engage the cat, make sure your stove top temp is 200-250 on start ups before engaging and wait 10-15 minutes on reloads.

I think my issue is that I'm using this stove in a way right now that it can't really work at it's best. If I put a full load in right now we'd have the windows open for hours. I'll see what happens when it cools a bit more over the next few days. Right now day time temps are in the upper fifties with no sun but night time temps are only around 48 to 50. By the weekend we are supposed to be dropping into the upper 30's at night with daytime highs in the mid to upper fifties and perhaps a bit windy. Thanks for all the input!!

 

[cbrodsky]

Once you know that you've gotten the stove hot enough to activate the cat, then indeed it will do well to slow it down, but in this case, it sounds like maybe you're still trying to engage it a bit too soon.

Once you get into 24x7 burning, this becomes a non-issue - the box stays hot so long that you don't have much of a delay when reloading. But from a completely cold start, you may need to give it longer before putting the cat on.

For that reason, I would not be as likely to suggest a cat stove to a casual burner who may not be running 24x7 - you lose some of the benefit.

 

[jqgs214]

I can smell this post going into cat vs. non-cat and the fact that shoulder seasons are easier with a non-cat.

 

[jpl1nh]

Once you know that you've gotten the stove hot enough to activate the cat, then indeed it will do well to slow it down, but in this case, it sounds like maybe you're still trying to engage it a bit too soon.

Once you get into 24x7 burning, this becomes a non-issue - the box stays hot so long that you don't have much of a delay when reloading. But from a completely cold start, you may need to give it longer before putting the cat on.

For that reason, I would not be as likely to suggest a cat stove to a casual burner who may not be running 24x7 - you lose some of the benefit.

It's possible that I'm engaging the cat to soon but I don't think so. From a cold start, its probably a good 45 minutes before I engage, the stove top is between 200 and 250 and flue temps are 400-450 or above. The cat obviously is engaging as I generally get a red glow within 2-3 minutes of engaging, stove top temps start to climb more quickly to about 400 to 450 and flue temps begin to fall back to 250 to 300. When I talk about slowing it down, I'm at the point where the flames are on the verge of going out. If I go a little too far they do go out and I get back puffing from the flames extinquishing, then re-igniting explosively. Even with no flames through that portion of the burn, the combustor is crankin! But even 15-20 mins into combustor burn, when it is damped that low, I get smoke out the chimney. If I open up the air and get gentle flames dancing again, the smoke goes away. I will be burning 24/7 when its cold enough, right now I'm burning about 6/5.. Not the most efficient use of the stove, but I love using it and hate turning the furnace on. Grudgingly though I would have to admit the furnace is probably more efficient right now. So the interesting point to me here is that while Woodstock agreed you could go too far damping the stove down and overwhelm the combustor (the customer is always right you know), I'm not hearing that as the experience of the other cat users here. Wxman, I don't think this is a cat non-cat debate cause I feel I'm burning right now at the margins of where either stove really would work its best. Actually, I still think it's better cat territory cause I'm working so hard at small slow fires.

 

[jqgs214]

Correct me if I'm wrong guys but most cat combustors light off at 500deg?(380 on some) seems a little premature on the cat engaging, but I guess you have no way of knwing the temp at the cat huh?

 

[jpl1nh]

Correct me if I'm wrong guys but most cat combustors light off at 500deg?(380 on some) seems a little premature on the cat engaging, but I guess you have no way of knwing the temp at the cat huh?

True, true, around 500 degrees is the safe time to light off the cat. On the Woodstock stoves, the firebox temp is approximately twice the stovetop reading once the stove is truly heated up, therefore a 250 stovetop temp equates to approximately 500 firebox. Because the Woodstock stoves are two layers of soapstone thick with an airspace between them, it takes considerable time for firebox temps to affect stovetop readings and it can be worthwhile to moniter flue gas temps as well. For example, after running the stove through a load, the stove top may read 450. When you add a fresh load, the firebox temp will drop considerably though the stove top temp will barely change. The stack thermometer will indicate that much more accurately, though probably reading a bit lower than the firebox temp. So despite the stovetop temp indicating the firebox is 2x450, you still need to wait approx 10 minutes or so for both the moisture to be driven out of the wood, and the firebox temp to come back up before re-engaging the combustor.

 

[Rhone]

Rhonemas, I think your point about cat stoves working well when turned down is quite true. However, I just spoke with Woodstock who agreed that it is possible to go a bit too far with that if your goal is a really clean burn.

I know that all too well, didn't know cat stoves exhibited that to some degree. With secondary burn units you need flames to reach up to the tubes above to keep it lit. If you turn ours down too much, you risk flames won't reach the secondary burn and only occasionally have it light it off or may even stop secondary burn from happening altogether. A cat turned down too much it may not be working at top efficiency but at least it's doing something a secondary burn unit you risk getting nothing.

I think the air handles are there to compensate for all situations and, you bring about a good point many don't realize they may not be best setting their unit to the lowest setting. I have a ranch my draft is nothing compared to someone with 2 stories and if I lower my intake to below about 40% my secondary burn starts to go off sporadically and I get blue smoke, at my lowest setting my burn lasts for like 14 hours (and I hardly get any heat and burns like crap with lots of smoke) so for me I just know that 40% is my sweet spot and I get the most heat/lb of wood, it took me a year to find it. I move my air handle up or down a little bit from there depending on how good the draft conditions are that day. My unit claims around an 8 hour burn so for me getting 8 hours with the air handle set to 40% sounds about right. My unit in a 2 story house with great draft they may need to have it near or at minimum to get the same 8 hour burn which, is sounds about right.

 

[cbrodsky]

OK, I'm probably going to jinx this, but may I comment that it's remarkable that we're all having such a civilized discussion on stove catalysts 15 posts into this thread!

:lol:

-Colin

 

[jpl1nh]

Rhonemas, I think your point about cat stoves working well when turned down is quite true. However, I just spoke with Woodstock who agreed that it is possible to go a bit too far with that if your goal is a really clean burn.

I know that all too well, didn't know cat stoves exhibited that to some degree. With secondary burn units you need flames to reach up to the tubes above to keep it lit. If you turn ours down too much, you risk flames won't reach the secondary burn and only occasionally have it light it off or may even stop secondary burn from happening altogether. A cat turned down too much it may not be working at top efficiency but at least it's doing something a secondary burn unit you risk getting nothing.

I think the air handles are there to compensate for all situations and, you bring about a good point many don't realize they may not be best setting their unit to the lowest setting. I have a ranch my draft is nothing compared to someone with 2 stories and if I lower my intake to below about 40% my secondary burn starts to go off sporadically and I get blue smoke, at my lowest setting my burn lasts for like 14 hours (and I hardly get any heat and burns like crap with lots of smoke) so for me I just know that 40% is my sweet spot and I get the most heat/lb of wood, it took me a year to find it. I move my air handle up or down a little bit from there depending on how good the draft conditions are that day. My unit claims around an 8 hour burn so for me getting 8 hours with the air handle set to 40% sounds about right. My unit in a 2 story house with great draft they may need to have it near or at minimum to get the same 8 hour burn which, is sounds about right.

I think you bring up another very good point, that being that each user has to find the "sweet" spot for their particular stove with their unique draft set up and the type of wood they are burning and the weather conditions. For me, that's what make using a wood stove so intriuging; that it is an art as much as a science.

 

[jpl1nh]

OK, I'm probably going to jinx this, but may I comment that it's remarkable that we're all having such a civilized discussion on stove catalysts 15 posts into this thread!

:lol:

-Colin

Yes, I'm very proud to say that it is possible to respect "the other side" and have such a civilized conversation. :bug:

 

[North of 60]

Rohnemas has it right. Cat stove are most efficient on a low slow burn. The cat needs temp, turbulance, and time to burn properly. Too much air and the smoke will rip right through the cat and won't have time to ignight. I know when I have a full load and the cat is glowing full bore I can see that white smoke or steam coming out my chimney for awhile then it turns to heat waves. You might not be waiting long enough to engage the cat, make sure your stove top temp is 200-250 on start ups before engaging and wait 10-15 minutes on reloads.

Both you guys nailed it. Awesome!Nice to know someone else has their brain working on how the cat operates. These stoves have a much larger advantage in the shoulder seasons because of this. Sept/Oct---Mar/Apr/ 50% of May I can Idle the stove on low safely. Good Discussion.

 

[Todd]

I know what you guys mean about finding the sweet spot. Right now with the relatively warm burning weather my sweet spot is half way between 0 and 1. As the weather gets colder it goes down to 1/4. There has been times I almost closed her off completely. To help me find these spots I painted the air intake numbers with high temp white paint and added a half mark between 0 and 1. It was really hard to see before because they were black on black.

Maybe these stoves could use a variation of the EBT. I know Colin talked about building one himself in another thread.