Question for those with Cats to feed. Does all smoke burn the same?

[Evil Dave]

I have been immersed into the world of catalytic burning for the first time this heating season. I have what seems to be decently dry Sib Elm as my main species of available wood this season. Other than making what seems to be a lot more ash than others seem to talk about, it burns well enough, lights quick, no sizzle, MC tests on my $15.00 meter at about 15% +/- 3%, but to get any serious heat I find myself running my Firev at about 1/2 throttle and having a moderately blazing firebox seems to be necessary to crank out serious heat. I recently burnt some of my Black Locust and was very pleased at the incredible improvement in all areas; ie. overall heat output, burn time, coaling heat output, very little ash created etc... And I think, but am not really sure, that the smoke even cranked more heat than I can generate off of a low flame-less firebox with the Cat feeding on Sib Elm smoke.
Thus my question. Does all smoke burn about the same? I know moisture/steam from unseasoned wood can really screw up what should be a good cat burn, but does the type of wood and the smoke they generate differ in heat output? Does it pretty much match what you might expect from the BTU chart for the wood type? With my Siberian Elm alone, I can run my Fireview with the air setting from 1 to 1/2 or even lower and it doesn't seem to increase the cat temp measured on my stove top therm nor the rear cat probe thermometer very much at all. I am doing good to reach 450 stove-top temp, 950 probe temp with a Sib Elm fueled, flame-less cat burn. I read of advised caution not to set the air too low for fear of the cat getting screaming hot, but I don't think my elm will do that even when I try to push it up there. I didn't experiment when feeding on BL yet because the weather improved and the temps warmed up enough to feed on Elm and keep up.
Just wondering what observations you veteran cat herders have made.

 

[Wood Duck]

I don't have a cat, but I do notice large variations in the secondary burn between types of wood. Black Locust seems the best, with oak also very good. Red Maple gives very good but short lived secondary burn. I don't get much with American Elm.

 

[Todd]

You will find a big difference in temps and heat output between wood species. The more dense the wood is the more fuel it has for the cat. I've burned lots of Elm and for me the temps will spike about the same as harder woods but have found they don't stay there as long. Keep playing with different settings, maybe throw a full load of Elm in there and leave it engaged at 1.25 for the whole burn and see what happens.

 

[jharkin]

You probably already know this but just to be sure I will ask the obvious question - Did you resplit the split before testing with the meter? Remember that even green wood will quickly become dry on the surface.

As to wood type I'm sure there are variations and less dense woods that burn hot and fast certainly put out the smoke faster....

 

[WoodpileOCD]

I think if you are having trouble getting to 1000* on the cat probe it isn't because of the quality of the smoke. Got a cat stove last Jan and was having the same issues with cat temps. I was absolutely thrilled when I could get it to 1100 our 1200 but my wood was definitely not as dry as it should be. This year I have much better wood and even with poplar and pine, the cat goes to 1500+ in no time. I run the stove without the blower a good bit depending on the weather and several times I've had to turn on the blower just to bleed off some heat because the cat was getting into the 1800 - 2000 range which I have read is not good for it.

Bottom line, if you aren't getting past 1000* it's probably the wood. To answer your original question, I've not seen much difference in cat temps with the type of wood smoke but definitely changes with the amount of smoke. Large loads = lots of smoke = lots of fuel for the cat = high cat temps.

Bear in mind on the type of smoke, I haven't done any study or real observation on this. Just thinking back over the last month and year.

 

[leeave96]

You will find a big difference in temps and heat output between wood species. The more dense the wood is the more fuel it has for the cat. I've burned lots of Elm and for me the temps will spike about the same as harder woods but have found they don't stay there as long. Keep playing with different settings, maybe throw a full load of Elm in there and leave it engaged at 1.25 for the whole burn and see what happens.

+1

Sometimes I burn some of my pine when I don't need as much heat, but want the light show. The most important thing is to keep your stove top from heading over 700 degrees. Keep playing with your stove and you will find your sweet spot for your set-up.

One thing about these Woodstock stoves, they are very responsive to damper settings.

You got a great stove!

Good luck,
Bill

 

[jackofalltrades]

I can not say that I have noticed any difference in smoke quality between species. I do notice good wood from bad wood and the amount of time it stays in the box and produces heat and the level of heat. I don't know if that is actually due to any difference in smoke quality though. I think its all wood properties.

 

[Backwoods Savage]

Does all smoke burn the same? I'd say yes, but some wood gives more smoke than others just like some wood will give more heat than others.

 

[Battenkiller]

Does all smoke burn the same? I'd say yes, but some wood gives more smoke than others just like some wood will give more heat than others.

Bingo! The quality will be basically the same, but the quantity can vary drastically. Softwood outgases faster than hardwood, dry wood outgases faster than wet wood, small splits outgas faster than large splits, and splits outgas faster than rounds. Your cat stove eats smoke for a living. If you want a lot of heat, you need to balance the smoke density and the incoming air. If you want more heat, your have to make more smoke and give it more air. All the cat does is to lower the activation energy needed to initiate combustion, you have to supply all the rest in the proper ratios to get the heat output you desire.

 

[Backwoods Savage]

See BK, we can agree very easily. :lol:

 

[Battenkiller]

See BK, we can agree very easily. :lol:

Sav, I think we would both have a ball sitting around tossing various hunks of wood in a stove, going outside to see the results, and coming back inside to discuss why we saw what we saw. We really ain't as far apart as you might think we are. ;-)

 

[Backwoods Savage]

Never did think we were all that far apart and yes, that very well would be enjoyable.

 

[Gark]

The only thing that seems to determine our cat's temp. is how much smoke at once it digests (after light-off). Species doesn't matter so much IMHO. On the low side , if I load the stove with too few splits (trying to cheat during shoulder season or get a short 2-hour burn), the sparse smoke won't maintain the cat's burn and it will stall out. Then the stove is like a pre-EPA airtight stove.

 

[pgmr]

A catalyst can only "process" a limited amount of smoke. If there is too much smoke (not enough primary air for the amount of heat in the firebox) or the dwell time is too short (too much primary air which doesn't allow the smoke to reside in the cat long enough), then smoke can make it through the cat unburned. The first can happen when shutting down the primary air inlet too quickly on a hot fire. The duration of smoke pass through is short, since the stove will quickly reach equilibrium. The second can happen for a long period of time if the primary air is left too far open. Since secondary combustion is often occurring in the firebox at these high burn rates (before the gases arrive at the catalyst), the amount of smoke being expelled is usually not visibly great.


Short dwell time is the reason catalytic stoves typically have a lower efficiency rating at high firing settings than non-cats at the same high fire conditions.

 

[Woody Stover]

With my Siberian Elm alone, I can run my Fireview with the air setting from 1 to 1/2 or even lower and it doesn't seem to increase the cat temp measured on my stove top therm nor the rear cat probe thermometer very much at all. I am doing good to reach 450 stove-top temp, 950 probe temp with a Sib Elm fueled, flame-less cat burn.

I'm not sure of the answer to the "different smoke" question. But I have found that the combustor probe on the FV/Keystone doesn't give an accurate indication of how hot the cat is burning. The higher temps at the cat and the tip of the probe dissipate over the length of the 8" probe, and the probe just indicates the temp near the flue exit. To get an accurate cat temp reading, you could do what Todd did; Drill a hole in the top of the stove over the cat and use a shorter probe. Now, you can get a rough idea by just looking at the cat and seeing how brightly it's burning. I think it would be hard to get a definitive answer to the smoke question, since other factors like MC of the wood samples used, split sizes, etc. come into play. The stove top lags behind stove interior/cat temps so that has to be factored in as well.

 

[Evil Dave]

To get an accurate cat temp reading, you could do what Todd did; Drill a hole in the top of the stove over the cat and use a shorter probe.

I don't think I'm ready to drill any holes in my stove just yet . . . . I'd like to really know but, drilling a my new stove? I'm not quite there yet.
I ran a small load of BL only through last night started on a good hot bed of coals and it seemed to be a little more reactive. If I push the entire stove temp up with an active flame big heat fire in the box, the cat always maintains or raises the stove top temp just a little once the cat burn sits in good. This was pretty easy to demonstrate last night. There still wasn't a major cat increase, but I only had 2 8" rounds and about a 9" split.

 

[WoodpileOCD]

A catalyst can only "process" a limited amount of smoke. If there is too much smoke (not enough primary air for the amount of heat in the firebox) or the dwell time is too short (too much primary air which doesn't allow the smoke to reside in the cat long enough), then smoke can make it through the cat unburned. The first can happen when shutting down the primary air inlet too quickly on a hot fire. The duration of smoke pass through is short, since the stove will quickly reach equilibrium. The second can happen for a long period of time if the primary air is left too far open. Since secondary combustion is often occurring in the firebox at these high burn rates (before the gases arrive at the catalyst), the amount of smoke being expelled is usually not visibly great.


Short dwell time is the reason catalytic stoves typically have a lower efficiency rating at high firing settings than non-cats at the same high fire conditions.

This is something I've figured out about my cat stove or read about or a combination thereof but this is the clearest explanation of the process I have seen anywhere.

Thanks