Great example of Huffing...

I witnessed the Cape Cod doing that at a dealer last winter. The sales lady jumped (scared her walking by) and then said, "I hate when it does that!".

I've had a few small puffs IN the stove when the afterburners lit up and went out a few times, but never enough to push smoke out of the stove. Yikes!

 

I don't know what that sales lady was doing! My Cod has never done this.
It's easily explainable in a top combustion stove, it could be a few things but is most likely a combination of unseasoned wood and restricting the primary air too far. The unseasoned wood is creating more smoke than the cat can handle and the gases back up in the stove, just like pumping the gas on an old carburetor-ed car and turning the key, BOOM. When the cat is struggling to stay engaged and the air is turned to low this is bound to happen I guess. I've never seen it in my Cod though.

 

Well that's not good for advertising....

 

Not blaming the Cod so much, although there were some reports last year that did show similar results with it. The one I saw was a fresh FULL load of what looked like less than dry wood, the air was shutdown, AND it was not very cold out. I was posting it more as a laugh, that I could not believe the store/dealer would be so stupid with customers walking around. Especailly the comment! I kind of chuckled and walked away. I was there to look at a big insert that had a blower attached o a 4" duct on the back of it which could be used to heat another room.

 

I'm going to jump in here and say my downdraft stove did the same thing no matter what.

You had to run it with the air control almost wide open to keep this from happening.
The thing is designed to be a box of smoke when it is running correctly, according to all the company reps I've spoken to.
And the whole box ignites unpredictably.

To keep a flame, the air was wide open, and we went through a lot of wood, and the stove could get hot.
I refuse to light it this year.

 

A downdrafter is any stove where the flue gasses are forced to travel downward at some point in their path from the firebox to the chimney. Almost universally you find downdraft setups in top loading stoves, its used so that the secondary combustion system can be placed in the rear of the stove and leave the top clear for the loading door. In placing the secondary in the back, you need to force the smoke to travel through it - so it must be in a separate chamber with a bypass to engage or disengage it (both cat and non-cat) and that bypass is usually a damper at the top of the stoves inner rear panel that opens and closes a straight shot into the flue exit (fireback).

When the bypass is closed smoke will take an alternate path to enter the rear combustion chamber. It either will be a second opening right below the main bypass, and being up high the smoke will then have to travel down through the rear chamber and then though a side passage back up to the flue exit; OR there will be an entrance to the secondary chamber at the bottom which makes the smoke have to travel down inside the main firebox to enter... like the old 1970s Vermont Castings 'horizontal burn' in the early Defiants, Vigilants and Resolutes.

In practice today there are two main categories of downdraft stoves:

Downdraft Catalytic
- VC Defiant, Encore, Intrepid, and catalytic inserts. Also the out of production Jotul F12
- With the bypass closed the smoke goes into a ceramic chamber in the back and travels down through the catalyst

Downdraft non-Catalytic
VC Defiant NC, Encore NC, Resolute Acclaim "Everburn" & Harman "Fire Dome" stoves
- With bypass closed the smoke goes into a heavily insulated rear burn chamber and mixes with superheated secondary air


The trouble with downdraft stoves in general is that because the smoke has to change direction multiple times there is a lot more restriction and they need a stronger than average chimney draft to keep things moving and work well. In a VC catalytic stove for example the primary air enters in the lower back, travels around the ash pan, up the side walls, forward to the airwash, down the front glass, throught the primary fire, into the catalyst intake hood, down through the cat, sideways out of the refractory exit, up through the back casting and then horizontally out of the rear exit! I count over 10 90degree turns in the path before it gets to the chimney liner.



Downdraft non-catalytics are especially temperamental because you have to generate those 1100F temps for secondary combustion away from direct exposure to the primary fire and without the help of a cat.

 

You can also add to your list of non cat down draft the Leyden from lopi. Their combustion system had the same designer as the VC "never burn", go figure!

 

Thanks jharkin thats a great description Ive never heard of that and now that I know about it I dont think I will ever look at something like that not that I think Ill ever give up my Fireview.

 

That picture of the convoluted air, smoke and exhaust paths is really neat, Jeremy. It looks kinda like a diagram of the on/off ramps where several freeways converge. I've never seen a schematic of the Encore and Defiant cat stoves - where did you find it? Good description of a downdraft unit too, thanks.

 

Jhark, great post, thanks! Scary diagram and description!

 

I found it in the manual for the 2140. The old manuals had a lot more useful information in them then the new 2550 manual. I did a lot of research during my rebuild.

 

As if the 2550 manual has ANY useful info.....

Jharkin and Defiant are damm near experts on this stuff, just sayin

 

Ha thanks man. I wont claim to be an expert, only at this for 4 years (though I did grow up with a first generation VC in the 80s). Im just a voracious reader and anal retentive enough to take my entire stove apart to try and make it perfect. I managed to learn a few things along the way by trial and a lot of error.

I can give you the magic formula to make the fireback of a vermont castings stove glow cherry red if you like

 

I got that formula.... 100y/o cedar split into kindling size splits+fill er up = nuclear melt down for sure.
Back to the op I have had this back puffing happen to me but it was due to 1. the air turned all the way down and 2. gaskets not being seated correctly. Is that youtube video from a member here? If not someone should recruit them and Im sure we could get them fixed up