Flue Temp okay to be lower when Cat active and blower on?

[rashomon]

The blower attachment for my Green Mountain 60 does an excellent job at extracting heat that would otherwise go up the chimney. Since I've gotten my FlueGuard probe thermometer (installed 18" above the stove on my double-walled pipe) I can watch Flue temps easily drop 300+ºF within minutes of turning on the blower.

I found this post from 2021 that asked about creosote buildup in low EGTs, but I wanted to expand on it specifically for when a Cat is active.

I've come to learn the dirties part of a burn is when you put in the new logs. I'm guessing that dirty burn lasts until the logs are burning well enough where there is no smoke/steam visible when I open to the door. It seems that could last up to the first 50% the life of the burn depending on how wet the wood is. This winter my wood has ranged from 5%-20%, with some pieces possibly higher. I try to avoid those logs. And I also try to avoid using the Cat when the wood appears wetter until all the moisture has burned off. In those instances I would make sure my EGTs are well in the optimal range (~400-800 indicated on my FlueGuard), ideally 500-600+ so the top of the chimney is hot.

But if I'm burning strong and clean, and my EGTs are 600+, and my Cat has been heated well into it's active range -- when I kick on the Cat are the creosote causing gasses burned off enough by the Cat so I can comfortably operate with a lower range of EGTs?

Once I kick on the blower full blast my EGTs can easily drop from 800 to 400. If my EGTs are lower to begin with my temps can drop from 600 to 300. It appears the "too cool" range on the FlueGuard begins around 375 so I'll often extract enough heat using the blower to dip into that "too cool" range.

But with the Cat functioning correctly aren't I safe to avoid creosote?

 

[EbS-P]

How is the stove vented??

I would be with dialing back to 400 with my 6” insulated liner up an interior chimney if climbed up on my roof and inspected my cap after two weeks of burning.

Un insulated probably not

 

[mellow]

Does the fan route the air over the top? I see the blower is mounted on the bottom. My concern is if the air is bringing down the temp of the cat (robbing heat faster than it can produce), are you monitoring the cat temp to make sure it is still active? Keep in mind the non-digital cat temp probes are not the quickest and lag behind.

 

[begreen]

when I kick on the Cat are the creosote causing gasses burned off enough by the Cat so I can comfortably operate with a lower range of EGTs?

Yes, as long as the temperature of the flue gases is over 250º when they exit the chimney. The question is how much heat loss is there in the flue system? If the stove was vented into single-wall stove pipe and then into an exterior chimney with no insulation then you can be sure that the flue gases could cool down a lot, maybe several hundred degrees. OTOH, if the stove is venting into double-wall stovepipe and then chimney pipe at the ceiling and up out the roof, the drop will be much lower.

One option with the current setup is to try running the blower on low speed when the flue gases are in the 400º range or not at all. Note that this only applies to the outgassing stage of the burn. Once the wood is all charcoal and glowing coals, the volatiles have been burned off and a lower flue temp is not an issue.

 

[rashomon]

Hi everyone. Sorry for my delay in responding back. I updated my signature to have the details of my flue system. I guess I was hoping so long as the Cat is active then I didn't need to worry so much about creosote. I wrongly assumed the Cat took care of all those gases and burned off anything that could cause creosote. So the past few weeks I've been burning on the low end of the flue guard temp probe, and that's just 18" above the stove. Sure enough, I see a good amount of creosote around the chimney cap. I guess I gotta burn hotter. But my Green Mountain 60 just doesn't get that hot. And if I burn with the air intake open I only get a few hours on the burn. Oh well. I'm burning pine...

 

[begreen]

Hi everyone. Sorry for my delay in responding back. I updated my signature to have the details of my flue system. I guess I was hoping so long as the Cat is active then I didn't need to worry so much about creosote. I wrongly assumed the Cat took care of all those gases and burned off anything that could cause creosote. So the past few weeks I've been burning on the low end of the flue guard temp probe, and that's just 18" above the stove. Sure enough, I see a good amount of creosote around the chimney cap. I guess I gotta burn hotter. But my Green Mountain 60 just doesn't get that hot. And if I burn with the air intake open I only get a few hours on the burn. Oh well. I'm burning pine...

Can you get some high-mountain spruce? It grows slowly and packs more BTUs than regular spruce.

 

[rashomon]

I didn't know that. I'll have to look around.

I live in a pine forest and am thinning out the trees near my house for fire mitigation so I have a near endless amount of ponderosa and lodge pole pines.