Questions about Encore Cat behavior...

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jharkin

Minister of Fire
Oct 21, 2009
3,890
Holliston, MA USA
Hi all-
Last year I was new here and many of you gave me great advice that helped me to get in the groove, unlearn all the bad habits from pre-EPA stoves and get my Encore to perform… I guess about as good as an encore can? Things seemed to really be in the groove this year but yesterday I had some odd behavior so let me explain and give me your thoughts. This may rample so skip to the end for my question if you like.

The setup –
I inherited the ’99 Encore 2550 when I bought the house. Ran like crap at first but found its mostly a mix of bad wood (of course!) and poor maintenance by the PO. I put in a new condar steel cat, replaced the refractory access panel (PO had put it in upside down blocking secondary air), replaced the worn secondary probe, tightened the door, and replaced griddle, ashpan and fire back gaskets (PO had put in new gasket on top of old cement  ). I also got a catalyst thermometer to learn how the stove reacts better.

This year’s wood is much better. ½ is 1 year old oak I bought in Sep-09 that has been drying in single rows in my yard since (total 2yr) and the other half is crabapple I split myself in Nov-09. The wood is all grey and split and a resplit moisture reading on a half dozen pieces average 16-18 on the apple and 18-22 on oak. Buring some in the fireplace I get no hiss and it lights off fast. So I think its *reasonably* dry...


The issue(s)-

So far this year the stove has been great. Running partial loads on 40F days I have been getting good heat, without any catalyst temp spikes and much longer burn times. Glass is staying relatively clean as long as I don’t run it on low air all day with a big load.
But then yesterday I did my first full load and it seemed to be back to its old bad tricks :( I had been burning it all day but let it get down to low coals (350F stovetop) around 5 and then did the first full load – packed it to the top with big splits and small chucks . Let it burn on bypass and closed it down with the griddle just under 500F. I didn’t want to let it get all the way up to 600F this time as already the entire load was flaming. I have a cat probe and usually it will show 500F in a minute or less than rapidly climb to 1000F+ in a minute or two. This time however it hit 500F car then just sat there. Slowly climbing to only 650F cat after 5 min, with smoke out of the chimney. I opened up the air and left it and 10 min later I found it finally hit 1200F cat and settled it down to cruise at 1/8 air. Smoke outside had cleared also.

Question 1 – any thoughts on why the sluggish light off?

A few hours of low burn later (now night, temps outside down in 20s) it was at 450 griddle/ 1100 cat but the room was cooling. I opened it up to 1/4. Come back 45min later I find the griddle at 500 and the cat at 1600. Normally this is just fine for the Encore but a look in the window and I see the draft hood and upper fireback glowing orange and flames shooting out from under the draft hood!
Now I have seen this before when it overfires. I think what happens is the iron gets so hot that the secondary air is fueling ignition of the smoke before the cat. But previously this only happened if I let the cat get away from me into the 1800+ range. It was strange to see it at only 1600F cat.

Question 2 – Any ideas on what’s different and how I could see overfiring behavior at what have been safe temps in the past?

My theory – trying to stuff it to the max I used too many small chunks. Then I closed the bypass too soon which at first smothered the cat. Maybe the sluggish light off left deposits that later on started burning off, then it overfired so hot that unaided secondary combustion before the cat kept going by itself keeping that area hot and burning off all the smoke leaving it cooler downstream?
If you agree my thinking is the solution is to use bigger pieces only to pack it for a full load, get hotter (550F+ griddle) before closing it down and then close down slower to help it settle in and not flood the cat.

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On a positive note, closing the air down cooled off the overfire condition in just minutes then it settled back into a nice 450 griddle/1100 cat cruise all night. I ended up with the stove still warm (400) with coals 12.5 hr later. My longest burn yet. I think I caught it in time not to warp anything but will check this week.

-Jeemy
 
Forgot to mention... Stove is hearth mounted with a rear exit flue into a 6in liner running up an interior masonry chimney. Total height is about 18ft to the cap. I can see insulation behind the blockoff but I'm not sure if they insulated all the way up.

Over the summer I cleaned it after burning <2 cord and got 2 pints of soot. Also thoroughly vacuumed out the stove including the refractory chamber and checked all the gaskets. The cat looked clean.
 
I had a wad of dust/fluff blocking the secondary air supply to the cat in my cat Defiant. I had vacuumed the chambers at each side of the refractory box, cleaned the catalyst, checked the secondary probe, before the start of the season... but you cant really get good access to the small air space behind the secondary air flap. When I shut the damper the stove was chocking up and back-puffing, one finall back-puff and it it blew out a big wad of dust and fluff from the back and burned fine again since!
Not sure if this was your issue or not of course.

Bill
 
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