Question on how catalyst works and the path of exhaust gasses.

[Hbob]

I have a new Encore with catalyst after using an older Encore with catalyst removed for many years. The new stove has a few holes at the bottom on the back wall/refractory which would enter the catalyst area below the catalyst. Then there is the main draft path above the catalyst. I am wondering about what goes through the row of holes? Is this just hot air to preheat the catalyst? Once it is heated, it burns the gases going out the main opening above the holes? Please explain what you know about the flow path. The manual and folks here on the forum recommend pushing the coals back against those holes when building fire and reloading. Is that helping to heat the catalyst? Are the gases burning on top of the hot catalyst or by going through the catalyst after entering holes? Are the holes there to keep catalyst hot for combustion above?
I will be posting a separate question in the temperature thread about the probe for the catalyst temperature.

 

[begreen]

When the bypass is closed, the wood gases are pulled through the holes into the secondary combustion chamber at the back of the firebox. After that they pass through the cat for final cleanup.

Vermont Castings Defiant and creosote

I have used my new VC Defiant since late Nov and i am still amazed at the creosote buildup! I reported earlier on this and your suggestions were helpful and utilized. Now, i have used seasoned wood, more than a yr old, and burned the fire at about 450, except during the night when I leave it...

www.hearth.com

 

[Hbob]

When the bypass is closed, the wood gases are pulled through the holes into the secondary combustion chamber at the back of the firebox. After that they pass through the cat for final cleanup.

Vermont Castings Defiant and creosote

I have used my new VC Defiant since late Nov and i am still amazed at the creosote buildup! I reported earlier on this and your suggestions were helpful and utilized. Now, i have used seasoned wood, more than a yr old, and burned the fire at about 450, except during the night when I leave it...

www.hearth.com

Above the small holes, there is a large opening that goes behind the back wall and above the catalyst on the way out the flue. So it does not appear that all the gas goes through the holes. I can see the flames going up behind the wall and visible through the opening you see at the top above the VC logo.

 

[Hbob]

Looking at the diagram linked above.....are the small holes the entry for the combustion air controlled by the thermostatic lever on right side?

 

[skb31]

The holes in your picture are where the secondary air flows into the firebox and the catalyst chamber. The secondary air is unregulated. If you were to remove the 2 ceramic plates (be very careful as they can break easily) you can then remove the cat and see your probe and you’ll notice those holes are below the level of the cat chamber.

The primary air control on the right side controls the air that flows down the front of the glass. You can see both air intakes at the bottom center of your stove. The lowest one with the grate type thing is your primary air and you’ll be able to see the flapper. The large, roughly 3x6 hole above the primary air is the secondary air intake.

 

[Hbob]

The holes in your picture are where the secondary air flows into the firebox and the catalyst chamber. The secondary air is unregulated. If you were to remove the 2 ceramic plates (be very careful as they can break easily) you can then remove the cat and see your probe and you’ll notice those holes are below the level of the cat chamber.

The primary air control on the right side controls the air that flows down the front of the glass. You can see both air intakes at the bottom center of your stove. The lowest one with the grate type thing is your primary air and you’ll be able to see the flapper. The large, roughly 3x6 hole above the primary air is the secondary air intake.

Thank you for that explanation. So the small round holes are bringing air from outside into the box. I was unsure which direction flow went through those holes. The slot above is obviously going from the firebox into the catalyst area. When the stove is cool in the morning I will take another look inside. I will take some more pictures with the back wall removed.

 

[skb31]

I have the same stove. If you read more of the temperature thread you’ll see some of us discussing fashioning a metal plate to cover the secondary air intake in case of an over fire. I have one ready but haven’t had to use it yet.

 

[Hbob]

I looked inside the refractory area in the back of the stove this morning before lighting fire. It appears the air/heat/exhaust from the main fire box goes in through the top of the catalyst and out the bottom to get to the flue. The small holes at the bottom of the refractory wall only feed the main box area, not the catalyst area. The probe, which is below the catalyst would be in the downstream heat zone between catalyst and the flue. I hope to hear from Woodcutter on this.

 

[JohnDaileyNH]

I looked inside the refractory area in the back of the stove this morning before lighting fire. It appears the air/heat/exhaust from the main fire box goes in through the top of the catalyst and out the bottom to get to the flue. The small holes at the bottom of the refractory wall only feed the main box area, not the catalyst area. The probe, which is below the catalyst would be in the downstream heat zone between catalyst and the flue. I hope to hear from Woodcutter on this.

@Woodsplitter67 getting called out

 

[gthomas785]

Yeah the holes are for secondary air, however note that this is not the only place where secondary air is introduced. There are also some channels in the refractory that deliver preheated secondary air directly to the catalyst from above.
The holes you see are delivering air to the firebox, but the air does not penetrate very far into the firebox when the damper is closed because the exhaust flow path draws most of this air up and into the catalyst chamber.

With the bypass open, secondary intake allows an unregulated amount of air to feed the fire directly (both through these holes, and by back feeding through the refractory chamber) which is why you can never get this stove to turn down very much in bypass mode.

 

[Woodsplitter67]

I looked inside the refractory area in the back of the stove this morning before lighting fire. It appears the air/heat/exhaust from the main fire box goes in through the top of the catalyst and out the bottom to get to the flue. The small holes at the bottom of the refractory wall only feed the main box area, not the catalyst area. The probe, which is below the catalyst would be in the downstream heat zone between catalyst and the flue. I hope to hear from Woodcutter on this.

the epa holes are right below the access cover. the epa holes dont feed the firebox at all.. your draft pulls all of the fresh air right into the catalyst chamber. Theres not alot of air moving through the holes anyway.. it's a small amount the holes are super small