Cat operating temperature

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tabner

Feeling the Heat
Jan 17, 2019
261
Eastern CT
I turned the air down all of the way because it seemed like temps were going to continue to rise above 500 uncontrolled even though it was at ~25% open. But I suppose it was an unwarranted worry given I was looking at my Rutland gauge which is reading high. I have an IR gun on order.

Is this a sign of insufficient draft or is this simply rushing the shut down process? How do people load the stove, set the air and then leave for work? Is this an hr long process?
Again, different stove model here, but also a hearthstone and I think we have determined basically the same firebox/Truhybrid cat setup. I have not mastered it yet, but your question about leaving for work has been on the top of my mind over the last few weeks, as i am in the same boat. I have to run a fire in the morning before i leave the house, lunch break when i run home, and again in the evening. I had the same concerns - as i was getting used to the stove i wouldn't feel comfortable walking away until an hour or two into the burn once i had most of the aggressive offgassing secondaries either finished or controlled, at which point the burn is half over and i just wasted all that time. So far my findings are:
the coal bed i reload on, and the stove temp when i reload, is very important. Pretty much prime operation for me would be catalyst still just barely in the active zone, and red hot coals on the bottom of the stove. If i have this, then i can open the bypass and the door, put in a full load of dry wood (i'm around 16% MC with maple and oak), leave the door cracked and wait till i get flames (sometimes takes 5 minutes of smoldering before ignition), then I latch door, let fire run with air intake full open for a couple minutes till it is well caught, engage cat, and then depending on how the load is burning, i start cutting back the air pretty quickly. i have found that cutting back my air quicker is actually helping me avoid the backpuffing. I think i was making the mistake of blasting the air full open to ignite the full load, and then cutting air back (as if i had a true cat stove) and this was causing the backpuffing - combined with my usage of the flue damper. I am now using my flue damper as a last resort / only after air is fully closed if needed. Basically i get the load lit, and then try to cut the air back in two stages, first stage is 50%, and second stage, about 5 minutes later is to almost fully closed. If i hit everything right with the reload timing and the air cut backs, i can have the whole process done in about 30 minutes and walk away and it'll cruise nicely for a few hours. I am finding about 3 hours of active burn with secondaries. and then another 3 hours of hot stove with bright hot coaling stage, and then things start to trail off. After an 8 hour nighttime burn i can rake the coals around and light a fire off with some kindling, no newspaper or matches required. But in the morning it will take me a bit longer burning on high to get the catalyst and flue back up to temp.
 

neverstop

Member
Oct 11, 2020
123
new hampshire
Again, different stove model here, but also a hearthstone and I think we have determined basically the same firebox/Truhybrid cat setup. I have not mastered it yet, but your question about leaving for work has been on the top of my mind over the last few weeks, as i am in the same boat. I have to run a fire in the morning before i leave the house, lunch break when i run home, and again in the evening. I had the same concerns - as i was getting used to the stove i wouldn't feel comfortable walking away until an hour or two into the burn once i had most of the aggressive offgassing secondaries either finished or controlled, at which point the burn is half over and i just wasted all that time. So far my findings are:
the coal bed i reload on, and the stove temp when i reload, is very important. Pretty much prime operation for me would be catalyst still just barely in the active zone, and red hot coals on the bottom of the stove. If i have this, then i can open the bypass and the door, put in a full load of dry wood (i'm around 16% MC with maple and oak), leave the door cracked and wait till i get flames (sometimes takes 5 minutes of smoldering before ignition), then I latch door, let fire run with air intake full open for a couple minutes till it is well caught, engage cat, and then depending on how the load is burning, i start cutting back the air pretty quickly. i have found that cutting back my air quicker is actually helping me avoid the backpuffing. I think i was making the mistake of blasting the air full open to ignite the full load, and then cutting air back (as if i had a true cat stove) and this was causing the backpuffing - combined with my usage of the flue damper. I am now using my flue damper as a last resort / only after air is fully closed if needed. Basically i get the load lit, and then try to cut the air back in two stages, first stage is 50%, and second stage, about 5 minutes later is to almost fully closed. If i hit everything right with the reload timing and the air cut backs, i can have the whole process done in about 30 minutes and walk away and it'll cruise nicely for a few hours. I am finding about 3 hours of active burn with secondaries. and then another 3 hours of hot stove with bright hot coaling stage, and then things start to trail off. After an 8 hour nighttime burn i can rake the coals around and light a fire off with some kindling, no newspaper or matches required. But in the morning it will take me a bit longer burning on high to get the catalyst and flue back up to temp.
How is "fully caught wood" defined? Does the entire load need to be engulfed in flames/charred, or just the top layer of splits?

And you never fully close the primary air? What stove top temperature does your stove operate at during the 3 hrs of secondary burns?

I also have a feeling I am waiting too long to engage the cat and shut down the air. At least on my last fire by the time I shut the air down to ~25% things were raging and it freaked me out so I completely shut the air down and then the backpuff occurred. Based on re-reading the manual and that experience it seems like small changes to the primary air below 25% have a large impact on how the fire burns.
 

tabner

Feeling the Heat
Jan 17, 2019
261
Eastern CT
How is "fully caught wood" defined? Does the entire load need to be engulfed in flames/charred, or just the top layer of splits?

And you never fully close the primary air? What stove top temperature does your stove operate at during the 3 hrs of secondary burns?

I also have a feeling I am waiting too long to engage the cat and shut down the air. At least on my last fire by the time I shut the air down to ~25% things were raging and it freaked me out so I completely shut the air down and then the backpuff occurred. Based on re-reading the manual and that experience it seems like small changes to the primary air below 25% have a large impact on how the fire burns.
sorry, when i say fully caught, i don't mean the full load (this is what was causing my backpuffing), what i mean is just caught to the point that i can start dialing back the air and it will remain lit. For me it's perfect when one side of the load catches fire and not the other, i can start dialing back the air and it all burns slower as it works it's way across the load. When i was fully engulfing the load and then shutting back air, i think this caused my backpuffing because now you have the full load out gassing aggressively, but you're cutting back air. and my description above was more with regard to a hot reload, so top layer of splits is not so much what i am referring to, i mean more the bottom splits have caught in one or two places.
I do fully close the primary air sometimes. Usually i go from full open, to 50%, and then to 90% closed. If i am home in the evening, and it's a large load of oak say before bed, i will come back 20 or 30 minutes later and close it 100% if it's still burning aggressively.
You may have to adjust all this though, your draft is probably less than mine.
As far as stove top temp i am kind of low, because i am pushing for longer burns right now, so i would say i usually peak the stove top around 550, ideally i get it to cruise between 475 and 500 for a couple hours, then during the 3 hours of hot coaling i would say i'm between 325 and 375.
I have a 6" liner that is also not insulated, however mine is 27 feet tall, and it's internal to the house, so presumably it stays at temp much better than your external. I also have the top flue exit off the stove (and then two 45s into the chimney and a 90 going up the chimney T).
 

neverstop

Member
Oct 11, 2020
123
new hampshire
sorry, when i say fully caught, i don't mean the full load (this is what was causing my backpuffing), what i mean is just caught to the point that i can start dialing back the air and it will remain lit. For me it's perfect when one side of the load catches fire and not the other, i can start dialing back the air and it all burns slower as it works it's way across the load. When i was fully engulfing the load and then shutting back air, i think this caused my backpuffing because now you have the full load out gassing aggressively, but you're cutting back air. and my description above was more with regard to a hot reload, so top layer of splits is not so much what i am referring to, i mean more the bottom splits have caught in one or two places.
I do fully close the primary air sometimes. Usually i go from full open, to 50%, and then to 90% closed. If i am home in the evening, and it's a large load of oak say before bed, i will come back 20 or 30 minutes later and close it 100% if it's still burning aggressively.
You may have to adjust all this though, your draft is probably less than mine.
As far as stove top temp i am kind of low, because i am pushing for longer burns right now, so i would say i usually peak the stove top around 550, ideally i get it to cruise between 475 and 500 for a couple hours, then during the 3 hours of hot coaling i would say i'm between 325 and 375.
I have a 6" liner that is also not insulated, however mine is 27 feet tall, and it's internal to the house, so presumably it stays at temp much better than your external. I also have the top flue exit off the stove (and then two 45s into the chimney and a 90 going up the chimney T).
yeah ok this makes sense regardless of cold-start/reload. I had been waiting until all of the wood was on fire, then started to cut down the air. Presumably this is what the manual states to do. Burning through the load one layer at a time seems like the most efficient way to burn and the most controllable.

Yes my draft is definitely lower than yours based on that description, but the general approach should apply.