Adventures running a cat stove with cordwood <12% MC

[Poindexter]

Forgive if it has been asked, but why not just split some fresh wood, and mix green in with your 7% MC stuff, to average 15 - 20% MC?

My 30.1's don't have anything blocking the probe in the convection deck. While my stoves are marked 30.1, they seem to be missing most of the features later 30.1's have.

Bringing in some dripping wet green wood to spike the punch has crossed my mind.

If I come up with a decent air dam to make the cat probe indicator more realistic with the convection fans running I'll let you know what I am using. If anyone has a 30.1 with this doohickey on it, can you measure its vertical height and maybe post a picture?

 

[Poindexter]

So here I am at T+30 minutes, not real excited about turning the Tstat down from "hi".



Convection deck fans are off. I feel like if I turn the fans on I could blow some heat out into the house, cool the firebox top and give the heat in the combustor somewhere to sink too.

Stack indicator is at 300.

House is up to 77 degrees. Screw it, I am following the manual, not overthinking it. I'm going to turn the fans on to high, so the fan setting matches the Tstat setting. And then I am going to change into some shorts.

 

[begreen]

I probably missed this but did you state whether this is single or double-wall stove pipe?

 

[Poindexter]

I probably missed this but did you state whether this is single or double-wall stove pipe?

Its double wall and the indicator is a magnetic surface mount. Highbeam and stumpshot have already made the point, but you might as well pile on too...

 

[Poindexter]

At T+60 I am still not inclined to turn it down.

What I am afeerd of is if I turn it down to far too fast the rich mixture I clearly got in there might ignite spontaneously instead of sequentially.

House is up to 82dF, the fan kit has been on high for 30 minutes, indicated stack temp is still "300" and I got this on the cat probe:



FWIW the cat is glowing a brighter blaze orange than any safety gear I ever saw, has been for a while.

That 300 indicated on the stack probe tells me I have unburnt fuel getting through the cat. I would really really like to see the cat probe temp peak and be headed back down before I fool with the Tsat knob.

I wonder what would happen if I turned the Tsat to medium -before- I close the bypass door.

 

[Poindexter]

I turned it down to 2.5, medium high. I am getting nervous, but the fuel load is well engulfed, I don't see any peaks of VOCs coming out of what is left in there.

 

[tarzan]

From what Poindexter said, with the cat probe needle buried, the cat has gotten too hot, regardless of the fact that the stove is "engineered so that the cats will not overheat." I guess the engineering failed. I wouldn't think that excessive cat temp for a short period, one time, would destroy the cat but I don't know.
Yeah, get your wood below 13%, and then ask yourself, if the stove is "engineered so that the cats will not overheat," why is this included in your manual?? (As an aside, BK should really think about proofreading the text before publication.) Also, I don't see any "closed or plugged" cells in the "severe" pic...
View attachment 185385 View attachment 185386
If the cat is indeed toast, as you and the dealer think might be the case, maybe the cat only burns well when there is a very fuel-rich environment in the box, and drops out of the active zone relatively quickly. Would the thermo then sense dropping firebox temp and open up the air, resulting in quicker consumption of the rest of your fuel? Seems likely that a bad cat may be the problem, not too-dry wood. But if not, could you stack the wood outside of the kilns in open air now and allow it to re-absorb some moisture? Maybe even let it get rained on a couple times.

Woody,

At T+60 I am still not inclined to turn it down.

What I am afeerd of is if I turn it down to far too fast the rich mixture I clearly got in there might ignite spontaneously instead of sequentially.

House is up to 82dF, the fan kit has been on high for 30 minutes, indicated stack temp is still "300" and I got this on the cat probe:

View attachment 185414

FWIW the cat is glowing a brighter blaze orange than any safety gear I ever saw, has been for a while.

That 300 indicated on the stack probe tells me I have unburnt fuel getting through the cat. I would really really like to see the cat probe temp peak and be headed back down before I fool with the Tsat knob.

I wonder what would happen if I turned the Tsat to medium -before- I close the bypass door.

FWIW, I have been there before and slammed the stat shut. Granted my wood is not nearly as dry as yours but I get my cat probe thermometer to almost exactly that spot during my shoulder season burn offs. Surely after an hour of burning wfo my wood is nearly equal as dry as yours?

 

[BKVP]

Poindexter! Haven't you any larger diameter logs to burn? With all that surface area, your load will burn much quicker.

PM me your address in FB. I have something to send you....no it's not a 24" diameter piece of Doug fir!

 

[Poindexter]

No, I don't have any bigger logs.

My preliminary plan for next year is to sell half the kilns on Craigslist and build a wood shed on that piece of lawn. When the remaining kilns get to 16% I can empty those into the shed and refill the kilns....

 

[Poindexter]

At T+80 I really hit something like 2.6 or 2.7 on the Tstat, but the stack probe is coming down to maybe 280 or so. So at T+90 I turned the Tsat on down to 2.3 and will go for 2.0 at T+100.

I don't expect the cat indicator probe to start lowering until the stack temp gets down to 150 or 200 or so, for now I think there is still unburnt fuel getting through there.

T+90 house at 86, stack at 280, cat probe blazing, fan kit on high, Tstat lowered from 2.7 to 2.3

 

[tarzan]

 

[Poindexter]

At T +100 stack temp is indicating 250, I was down to a few ghost flames and now I am at straight medium on the Tsat with no visible flames in the box.

I am going to let that ride a little while before I turn the deck fans down from hi.

 

[begreen]

Its double wall and the indicator is a magnetic surface mount. Highbeam and stumpshot have already made the point, but you might as well pile on too...

I read that but wanted verification. The surface temps on double-wall are not helpful. Order a Condar probe for a more informative reading.

 

[Highbeam]

I hope I'm right with my understanding that the stove is engineered to prevent cat overheating. I know @BKVP wrote that but I too am dealing with low to sub teen % moisture wood. No big deal to replace the cat but what about the rest of the stove?

 

[Highbeam]

The outside of that double wall looks like it got really hot. I know you run it hard but the flue shouldn't be so hot.

 

[tarzan]

I hope I'm right with my understanding that the stove is engineered to prevent cat overheating. I know @BKVP wrote that but I too am dealing with low to sub teen % moisture wood. No big deal to replace the cat but what about the rest of the stove?

The stove can take it.

 

[Poindexter]

I hope I'm right with my understanding that the stove is engineered to prevent cat overheating. I know @BKVP wrote that but I too am dealing with low to sub teen % moisture wood. No big deal to replace the cat but what about the rest of the stove?

I ran a few loads of 11% a time or two before just like regular wood. Certainly a nail biter the first time through, but nothing quite like the above.

I am pretty sure it is under 11%MC you have to start worrying/watching for a air fuel mix so rich that it might cook off all at once instead of smoothly.

 

[Poindexter]

The outside of that double wall looks like it got really hot. I know you run it hard but the flue shouldn't be so hot.

Yup, you are like the fourth person to mention that today. At this point I am not going to ask the wife about it so much as explain why i really need to get a flue probe with a sensor inside the lumen of the pipe.

 

[Highbeam]

Yup, you are like the fourth person to mention that today. At this point I am not going to ask the wife about it so much as explain why i really need to get a flue probe with a sensor inside the lumen of the pipe.

Condar makes the oem cat meter and seem to make a dang good probe meter for the flue too. The paint is way better on their flue probe meters than the bk cat meters.

 

[Highbeam]

The stove can take it.

I hope you're right.

 

[Poindexter]

At T+120 I turned the fan deck down to med, H =87, S = 200, Tstat 2.0, cat probe at E in active.

At T+150 the excitement was over, H =86, cat probe 1/4" below A in active, stack 175, tstat down to 1.0 from 2.0, fan deck from med to low.

At T+210 house 85 (I left the sliding glass door open briefly when checking my stack plume), stack 150, cat halfway between inactive notch and A in active, Tstat 1.0, fan deck low. I got a big pile of charcoal in there still, I suspect it will run several more hours though I won't be staying up with it.

Besides a new stack temp probe that reads inside the pipe, and a new cat temp probe with numbers on it, and a home fabricated windshield so i can run the fans without falsifying the cat probe temp reading, and a new telescoping pipe to replace my overheated one... sheesh.

What else am I going to need to figure out how much sooner in the burn I can start turning the Tstat down?

I have a hunch I really need to know the mass of the fuel in the firebox on an ongoing basis to make a safe informed decision about when to start backing off on that Tstat knob. Did you ever try to apply sandpaper to the hind end of a rabid panther while locked inside a phone booth with said panther?

It bugs me that my stack temp is so high. I have been running that same sensor on the same pipe for years, I am accustomed to seeing 100, 150, maybe 175 on that stack sensor when the stove is running at its best. Doesn't matter if that 300 was from pure CO2 in the cat exhaust plume or unburnt fuel making it through the cat and burning in the pipe. Either way that fuel was heating the neighborhood instead of my house.

 

[Poindexter]

I hope you're right.

11%, 12% is fine. I have burnt a lot of it, probably more than 2 cords. When the cat probe says active close the bypass door, run with Tsat on high for 30 minutes, adjust the Tstat to whatever you want, come back in 12 hours.

Its like candy for my Ashford, and you can throw baseball size blobs of spruce sap 2 or 3 at a time in with wood that dry too.

Of course your telescope pipe might end up looking like mine ;-)

My stove passed the dollar bill test at every test point in the last five days.

 

[Poindexter]

Talked it over with the wife. I am going to upgrade my instruments tomorrow, and replace the telescope in few weeks when I have good data.

Anyone have a pic of the cat probe windshield on a Ashford 30.1? Bueller? Bueller?

 

[Woody Stover]

What i am seeing is if I fill the stove in the AM and go to work deeper into winter I am going to have a cooling cat already below the A in active when I start my lunch break. By the time I get home for a reload I am going to have an inactive cat.
At 12-16%MC this would have been a 10-12 hour burn with outdoor ambients in the neighborhood of -20dF, given my static insulation envelope. So where did my burn time go?
I _think_ what I am up against this year is figuring out how soon I can turn the Tstat down to medium. Some number less than 30 minutes that increases my burn time (back to 'normal')

So you're saying that with the 16% wood, your cat would be in the active range for 10-12 hrs, and now it's only active for maybe 5 hrs? Seems to me that if your super-dry wood is burning faster, your stove should be hotter and the thermostat should cut the air correspondingly, correct? I don't see how cutting the air to medium maybe 10-15 minutes sooner is going to gain you much burn time, but...

In "winter" I use a box fan on the floor in the hall to push cold air out of the floors of the bedrooms towards the stove. I spend 5-6 months annually tripping over that fool thing

Maybe try a tower fan; That would have a lot smaller footprint and might work pretty well.

i have only been able to get to engaged cat and clean plume from a cold stove inside the legal 20 minute time limit by keeping both the loading door and the bypass door open until the combustor is hot enough to engage.
This year using the same process but drier wood I am getting some cold start to clean plume times in the 12-15 minute range.

Looks like you are loading the stove N-S...is that what you were doing last year when you had longer burn times?

Wouldn't it be ironic if our stoves would emit less grams per burn if we were allowed to heat the cat with a smaller longer fire instead of smoking like a coal fired locomotive for 18 minutes trying to meet the 20 minute limit?

With my little Keystone, cold stove, I usually start a top-down fire and there's virtually nothing coming out of the stack. It takes a little longer to get the stove up to temp than it would with starting the load burning more toward the bottom and getting a bigger fire faster, but hey, the plume is clean! If there are some coals, I can shove them to the back where they won't get much oxygen and won't ignite the bottom of a fresh load, and I can still do a top-down. Obviously when it's cold out and you need to reload before the coal bed burns way down, you just have to stuff in another load on the coals and smoke-bomb the hood for a while.
Now, what I did with the Buck 91 is what you are describing with a "smaller, longer fire." Since it's a big stove with a lot of metal to get up to temp, I would just burn a few small splits in the box for a while to get the stove temp up, and get a few more coals. Once I was closer to light-off temp, I would load 'er up N-S with the coals in the center and put the fire to it, getting the center of the load going. But that little pre-heating fire burned pretty darn clean...

 

[Poindexter]

@Highbeam was right again, most recently for me as "much fuel is puked up the flue during startup."

This morning at 0520, T + 732 aka 12:08, I still had coals on the floor of the firebox, the house was at +77dF, and the cat was far enough up into the inactive zone I just know I could have gotten in active again in 15 minutes or so. I didn't quite have enough hot coals for a hot reload this morning, but I think if I can turn the Tstat down even 30 minutes sooner I would have had a legitimate 12 hour burn.

So, much fuel puked up the stack during startup, absolutely. Hours and hours of burn time's worth.

Still looking for the height of the windshield that goes around the cat probe to shield it from the deck fans on a Ashford 30.1.