Bizarre Vermont Castings Defiant Issue

[mloring]

Going on my fourth winter with this temperamental beast. It's a Defiant 1975 CAT-C. Last winter I found a wad of what looks like ceramic insulation batting on the floor behind the stove, just below the air intake. Unfortunately I didn't get a picture of it. However, I'm getting the stove ready for this winter and need to solve this mystery. Where did it come from and is it something I need to replace? I got around back and under the stove today, and took some pictures of where it came from. There's still a wad of material stuck up in there. And I'm getting soot out of this opening when I clean the chimney. That can't be right. I do sometimes get some back drafts at night when the air intake is turned all the way down, which pops the griddle open and blows puffs of smoke out...another separate and frustrating issue with this stove. But could that have dislodged or blasted something open at the back of the stove? I've looked at the exploded diagram and it's no help whatsoever in figuring out what should be there. Any VC experts have experience with this?

 

[mloring]

Or maybe someone knows what the second opening above the air intake is for (this is where the wad of insulation came from and the soot falls out of)? It seems like this is an unrestricted opening for air into the chimney...which would explain why the two chimney fires I've had with this stove have been unextinguishable via restricting air through the primary air intake and damper.

I really can't believe this stove is legal to sell. Were it not for a well-designed chimney, it probably would have burned my house down by now.

 

[Todd]

I’m not that familiar with your stove but I know the secondary burn chamber and catalyst are surrounded by an insulation refractory that after time needs replacing. Looks like that time has come for your stove?

Many people come to this forum over the years with VC stove issues. Very finicky to operate properly, requires very dry wood and optimum draft.

 

[arnermd]

Or maybe someone knows what the second opening above the air intake is for (this is where the wad of insulation came from and the soot falls out of)? It seems like this is an unrestricted opening for air into the chimney...which would explain why the two chimney fires I've had with this stove have been unextinguishable via restricting air through the primary air intake and damper.

I really can't believe this stove is legal to sell. Were it not for a well-designed chimney, it probably would have burned my house down by now.

A long time VC victim here... I have been suffering with a 1975 model for 13 years.

I am not sure what that is.... it looks like refractory board (manual calls it "back insulation board") but it should not be able to get to that opening unless your refractory is broken. That board is fairly thick like 3/8" - 1/2" as I recall. The only other thing I can think of is maybe it is some gasket material from around the refractory seals? Those are thinner like maybe 1/8" thick sheets. Look at the pics I have in the links below.

Have you looked at the cat / inside the refractory? If you are getting crumbs from the chimney out of the secondary air inlet it tells me the back side of the refractory has failed. But it should be easy to see once you remove the covers and inspect the cat area. I have failed and replaced two refractory engines over the life of my stove. Latest one has 5 seasons on it...

That inlet above the primary air damper is the Secondary air inlet. It allows air to flow into the secondary burn chamber (where the cat it is). There are several holes low on the fireback that meter the air in and there are some other passages that flow up the side.

See posts here for descriptions:
https://www.hearth.com/talk/threads/2022-23-vc-owner-thread.193685/post-2640453
https://www.hearth.com/talk/threads/2022-23-vc-owner-thread.193685/post-2650369