Catalyst active but smoking

[trucklyhow]

Why would I be seeing lots of smoke when the catalyst is fully glowing and the indicator is well into the zone?
Here are all the factors I can think of:

• Ashford 25 insert, 2 years old. Original catalyst.
• Burning the first reload of the day, an hour into the burn.
• Today's outside temps low 50s (F)
• Wood is a mix of oak, maple, and locust. I can't entirely vouch for moisture but it has all been stacked for 2 years.
• Smoke is not black, brown, or white, just a neutral grey. Looks like a lot of it, like what I'd expect to see from a non-EPA stove or fireplace.
• Intake is set around 3 o'clock, but I have tried adding more and less and neither adjustment seems to affect the amount of smoke.

Happy to answer any other questions if anyone can provide some thoughts or suggestions.
Thanks

 

[trucklyhow]

(Clarification: this is the second burn of the day, started with lots of hot coals, got back up to temperature quickly.)

 

[stoveliker]

Is this smoke a new thing or was it always like this?
Is it continuous smoke or off and on?
How much do you burn per season?

Are you sure the bypass is properly closed? (I'm not sure how this works for an insert; in a freestanding stove there is a distinct cam over feel when one closes it.)

 

[trucklyhow]

Is this smoke a new thing or was it always like this?
Is it continuous smoke or off and on?
How much do you burn per season?

Are you sure the bypass is properly closed? (I'm not sure how this works for an insert; in a freestanding stove there is a distinct cam over feel when one closes it.)

Thanks for your questions! I think the issue is new this winter; I don't recall it happening last year. When it's happening it's continuous for a period of time (like an hour or so) and then at some point the smoke stops and I just see clear heat. But I never have an opportunity to sit and watch the chimney for hours on end so I can't vouch for that 100%. This winter we went through a little less than three cords. The bypass on the insert is controlled by a handle that slides straight in and out. When closing the bypass, there is no "cam over" but there is a distinct "clunk" of the handle reaching its limit. There's no way that I know of to verify that the bypass door is really closed all the way, though.
If the issue is a failing catalyst, would it still glow even if the catalytic reaction isn't happening?

 

[stoveliker]

Hm.
It is known that the system can smoke for a while after the air input is changed (either by the user moving the thermostat, or by the thermostat adjusting itself a bit).
The fact that you still can have clear exhaust, and a clearly active (glowing) cat suggests to me that it's not the cat failing - which would indeed be very early after 2 seasons (though its lifetime is not measured in years but in hours burned, hence my question about how much burning).
In my view 6 cords in total is unlikely to result in a cat that is near failing.

If this hour of smoke is right after charring the new load, then I do think that is a bit long. I would suggest to either char the load a bit longer and/or dial the thermostat down to your desired heat output a bit slower (i.e. in more steps, with 10+ minutes between them).

Finally, how tall is your flue from top of the insert to the cap? A very tall flue might result in high draft, which could "suck too hard", leading to lower residence times of the exhaust gases in the channels of the cat, leading to less effective combustion there.

 

[begreen]

Check the bypass action to make sure it is sealing closed. While there, look at the face of the cat to see if it is getting plugged with ash.

With temps in the 50s draft will be weaker. How tall is the flue system the insert?

 

[trucklyhow]

Thanks folks, I will check these fsctors and see what improvements they might make. It's about 30 feet.

 

[stoveliker]

30 feet is (too?) tall, especially if straight up.
Though in this weather (warmer outside temps), the draft will decrease as compared to midwinter.
I don't know how a 30 ft chimney in 50 deg weather would draft, but if (still) too much, it could decrease the residence time in the cat by too much, leading to incomplete combustion of the smoke.
Did the installer measure (!) the draft to show it's in spec for the Ashford? Not many do - but with a chimney this tall, it should have been a concern from the start.

The solution would be a key damper - but that's hard (not necessarily impossible) in an insert.

I think @Ashful has a (freestanding) Ashford on a similar chimney and does use a damper - I just don't know about its use in the current outside temps.

 

[Ashful]

I would not ever want to go back to running my Ashford on 30 feet of pipe without a damper, it can be done, but it's touchy and prone to cat plugging. I've even been contemplating adding one to my shorter chimney (15-18 ft), as even that is more reactive to chimney temperature than the tall pipe with the damper.

 

[stoveliker]

What's your damper setting at 50 F? Still significant?

 

[Highbeam]

Is that 30 foot masonry chimney lined with a 6" insulated liner?

 

[Diabel]

My 2018 (installed) Princess has been sending light grey smoke up the pipe from the beginning. Many kind people tried to help. I eventually gave up. We are in 2024….it will send grey smoke for two three hours after closing the bypass, then nothing for several hours then more smoke. It will smoke with the cat bright orange and then it will smoke with the cat all black. Zero consistency. I gave up. Disclaimer, I use the stove very occasionally several weekends in the fall and several weekends in the spring.

 

[Ashful]

What's your damper setting at 50 F? Still significant?

Draft is governed by difference in temperature between top of chimney and bottom. When the temperature at the bottom is 600F on a high burn, the difference between 20F and 50F at the top really makes very little difference.

My optimum damper position tends to be somewhere between totally horizontal/closed, and perhaps 5-10 degrees off that position... maybe 80% - 90% closed. It varies more with build-up around the damper throughout the season, than with outside temperature, I think.

I guess we could almost plot it as a sine/cosine function, depending on whether you call horizontal or vertical "zero", and that would put 10 degrees around 98.5% closed on a perfectly sealed damper. Of course, they're a bit undersized to the pipe, and have a few ventilation holes in the casting, which is why I'm guessing 80% - 90%.

 

[stoveliker]

Ah, yes, 20 vs 50 makes sense.
Though this would suggest that warm weather burning should not be an issue for draft - for which there are plenty counter examples.

Anyway, your experience shows that 30 ft is too tall, even for shoulder season burning.

 

[begreen]

You are correct. The fact that 400-600º flue gases are present does not change the differential between indoor and outdoor temperatures. This and the height of the flue are primarily what drives draft. That's why even a 20' tall system that drafts well can have smoke spillage upon opening the stove door when there is a 20º differential and none when there is a 40º differential. But... the flue gas temperature does have a direct bearing.

I think in engineering terms, (correct me if this is wrong), draft is determined by

• Density of gases at the inlet of the chimney – Flue gases density at the inlet of the chimney is dependent upon the temperature of flue gases entering the chimney, measured in (Kg/m^3).
• Density of gases at the outlet of the chimney – Flue gases density at the outlet of the chimney is dependent upon the temperature of flue gases exiting the chimney, measured in (Kg/m^3).

Height of chimney – Draft developed by chimney is directly proportional to the height of the flue, so height the chimney, more will be the draft. Chimney height is measured in (m).

In other words, cold starting in mild outdoor temps can be miserable unless the chimney is quite tall.