2022/23 VC Owner thread
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I like it plenty. I burn Pennsylvania hard coal (Anthracite). Not the soft Bituminous that billows out yellow smoke and high sulfer smell. Anthracite will have no smoke and virtually no smell if burned properly save for a little on start up and re-loads.
Woodsplitter67
Minister of Fire
Put a decent magnetic one on there.. You may be stalling.. you'll be able to rule that out as a possibility
I have had similar problems getting my cat up to temp today. Small fires and low draft. Let the cat sit there plugging away for an hour, best it could muster was 550. Threw in 2 fresh splits on a hot bed of coals, immediately engaged the cat and off it went.... 1100 - 1300.
Almost sounds like you have an air leak in the secondary that is quenching the cat. As @Woodsplitter67 said. Where are you measuring the cat temp? Right downstream of the cat in the typical factory provided spot?
My stove is running wonderfully today, not sure if it was my door adjustment, low draft day or just smaller wood loads. Guess I will find out when it gets cold again. Draft is definitely running lower than it was last week. 0.09 - 0.1 iwc today. Last week was .1 - .14 iwc. Maybe a clue....
xanadu1797
Member
I’m going to check the ceramic fireback tomorrow and see if it’s wiggly. Not sure how else I could check for an air leak between the firebox and the refractory….?
xanadu1797
Member
Ok youse guys, I’m asking for the crown jewels here, the secret knowledge:
How does the primary/secondary air flow in the firebox/refractory? Why does an air leak between the firebox and the refractory assembly lead to a cat temp drop with the secondary open?
How does the primary/secondary air flow in the firebox/refractory? Why does an air leak between the firebox and the refractory assembly lead to a cat temp drop with the secondary open?
xanadu1797
Member
Woodsplitter67
Minister of Fire
If you look at the stove manual/service manual.. You will see that the air enters the back of the stove and the air goes 2 ways 1 in the primary air wash and ales the secondary air out of the 8 or so holes
Were all a little older so Ill use this analogy.. Its like a 4 barrel carb on a 350 engine.. The jets are at the top of the carb and the fuel and air are mixed as it goes down the carb into the combustion chamber.. if the jets are at the bottom of the carb the fuel in not mixed and your getting mostly air
If your air is leaking and not going out the EPA secondary air holes and leaking past the gasket going right into the chamber your not going to get secondary combustion.. no air and fuel is mixed.. most of the air from the front of the stove is burned from the wood in the box.. The air in the secondary leaking in just going directly into the cat chamber.
Here it comes, brace yourself..... It is not easily explained in words. I did not really understand until I rebuilt my stove, twice....
These pictures are from the Defiant 2n1 rebuild manuals. I believe your encore 2040 is identical except for the size of the firebox.
There are actually 2 inlets, primary and secondary: Notice the primary has a flapper on a wire hinge / lever. The cable you see there goes to the primary control lever on the right side of the stove. The primary air (green arrows) comes in and travels through some gasketed passages, up the side of the stove and dumps into the firebox through the air wash vent just inside the glass doors at the top.
I believe the rear refractory piece is called the "engine", it has a channel around the perimeter and a series of small holes that feed into
the secondary burn chamber. These holes get enclosed by the fire back plate and gasket once it is installed.
Plate and gasket installed, notice there are three openings that the air can travel through the gasket towards the front of the stove.
Once you install the fireback we see the 8 holes that @Woodsplitter67 referred to and two more side channels
Once you install the inner plate..... you can see this is where the smoke enters and mixes with the secondary air. Which then turns around behind the inner plate and enters the cat.
Here is where I would love to hear from a VC combustion engineer....
- I believe the design intent here was that air coming in the 8 holes at the bottom would be drawn up into the exhaust gas via the draft. I suspect some of that air leaks into the firebox and actually supports primary combustion. This is not good because as the stove operator I can not control the air flow there. That flow is only determined by the draft and the size of the 8 holes. which I have no active control over.
- The 2 side channels are are of great interest to me. As you can see here the air coming through there can not go directly into the inner cover chamber, it needs to works its way down and around the edge of the inner cover. I also suspect some of this air gets mixed in with the primary combustion zone and supports the primary combustion, again uncontrollable by me as the operator.
- Because the smoke inlet is very low in the firebox there is also the potential to "vaccuum" off a bed of coals or even active flames. I believe this is leading to flame impingement on the cat under certain conditions. I suspect this why our 2n1 cats only last 1-2 seasons and are not warrantied by the Firecat or Condar.
- I believe the older cat designs (the ones with secondary temp air control) the smoke inlet is higher in the firebox (reduced probability of flame impingement) and the secondary air is injected directly into the secondary smoke channel. There is no possibility of secondary air back mixing to promote primary combustion.
- Also the older cat designs have a bimetal spring which opens and closes the secondary air shutter. I believe the design intent there was to reduce the amount of secondary air (and reduce the rate of combustion) in the event the cat overheats. This could lead to incomplete combustion due to a lack of oxygen but at least there is some regulation of air to prevent runaway cats. I am guessing here, sure would love to hear from VC what the thought process was for both designs.
If you have air leaking in downstream of the cat then you get what @Woodsplitter67 described. No secondary combustion on the cat.
You could also be leaking too much air upstream of the cat which will cool the combustion gases and your cat never reaches the light off temp. You could be "quenching" the combustion gas stream to the point where the cat never gets hot enough to light off.
xanadu1797
Member
wow! that's amazing and pretty involved. Thanks to you both for explaining this sucker to me. I guess I'll tear it down again in the summer and try to find my air leaks.
You should be able to see a lot without tearing it apart. If you remove the covers and the cat you can see almost everything. i woudl satrt by looking and see what you see...
Are you sure you have an air leak..... as I said yesterday I could not get my cat hot for hours, stalled at 550.... Finally with a good bed of hot coals and fresh wood it lit off. I blame it on a low draft day, small loads and intermittent running.
xanadu1797
Member
Yeah but after I refitted my stove I closed off the secondary as a result of convos I saw on here. I nuked the last two cats and thought I had a problem with running the stove hot so preemptively closed it off. to protect the new ($800 in parts). After running it nicely for a month and a half I took off my secondary air blocking and the cat sinks like a stone. Totally threw me for a loop. Getting to understand now the possibilities
Woodsplitter67
Minister of Fire
You dont need to do that.. take 3/16s gasket and lay it across the gap in the cat chamber.. that should plug the leak for now.. just stuff it in the crack where you see the gasket between the fireback and the refractory.. this will also confirm the issue
xanadu1797
Member
Woodsplitter67
Minister of Fire
xanadu1797
Member
Best I can make out the manual says the operating range of the cat is 500-600 F. Funny because I know that’s not true but it makes me wonder if my 700-800 degrees might not be so bad. I’ll have to study the smoke coming out of the chimney after a reload.
Woodsplitter67
Minister of Fire
that says ignites.. not range.. the cat ignites between 500/600 degrees
There are air passages there, those scalloped out channels allow for secondary air so I would not block those if you can avoid it. Maybe use sections of rope. My guess is they are not that critical..... but I am just guessing.
Also you don't need to jam it in there, a little bit just to fill up the gap will work fine. You don't want to create a wedge there that could crack the refractory when it gets hot.
Interesting is says the "element is a metal honeycomb"..... I did not realize they were offering metal cats for these models. I have only seen ceramic versions.... Is that right? Anybody tried one in a 2n1 stove?
Woodsplitter67
Minister of Fire
The Intrepid flexburn only comes with a steel cat. A ceramic cat is not available for this model. The steel cat is supposed to light off a a slightly lower temp than a ceramic one. One disadvantage is the steel cat has smaller holes which may clog easier but it has been said since the opening walls are thinner they may slice through any ash that hits it. Maybe a wash.
Where did you buy the steel cat? I think the Defiant 1975 and the Encore 2040 use the same cat, right?
I rarely need to use kindling to restart from night before unless it is too warm for that afternoon and I let it die
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