(Encore) Cat sluggish on big loads? - UPDATE: Your advice worked! - see last post

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jharkin

Minister of Fire
Oct 21, 2009
3,890
Holliston, MA USA
So on my third winter now I'm having muuuuuch better results. Dryer wood= better burns, little glass cleaning, easier to control etc.

But one problem i still have with the catalyst. On medium loads of 3-4 splits I have no problem getting it to light off. Once I get a good bed of coals I just reload and let it burn wide open till the load is fully charred and the stovetop hits 550-600F. Close the bypass damper and very quickly the catalyst probe temp pops to 500 and starts climbing quickly to 1000+. I know its lit off right when I see it jump 50 degrees every 5 seconds or so and hit 1000 within a minute. It will usually cruise between 1100 - 1500 depending on load and draft.


Its the big overnight loads I have a problem with. when I pack it to the gills the above method wont get me a reliable light off. ( And by packed I mean packed - I push the coals front, load splits E-W pushed against the left side and put a couple small ones upright on the right to fill in then fill it to within an inch of the griddle). Often I will get he cat probe temp to climb sluggishly to 650~700 then just sit there. I'm finding I either need to burn wide open and push the stovetop to 700 before shutting hte bypass(by then the andirons are usually glowing) or else just leave it for a half hour or so as it slowly rises up to temp. Its only when the cat probe temp gets to 1100 or so that the smoke out of the stack will fully clear.

My wood is a mix of oak, maple and and old crabapple, all of which has been split and stacked in single rows in my yard now for 2 full summers. I resplit and checked a couple pieces and the internal MM readings are 15-18%.

The catalytic combustor I replaced in fall 2009 with a Condar Steelcat. At this point its probably got less than 6 cords through it as Im only a weekend burner. I get only a coffee can or so of fine black soot on a cleaning once a year so I think its generally doing its job. I did have a couple overfire scares and got it over 1800F twice for short times... not sure if that was enough to poison the element. This season I gave it the full vinegar/distilled water boil treatment but it really didnt have much build up.


BTW, otherwise this Encore stove is in good shape. The refractory is holding up well and Ive replaced every gasket but the damper and all checkout fine on the dollar bill test. I dont have any drafting or controllability issues to speak of.

Any ideas... or is this normal and I just simply need to get those big loads hotter to burn off the water?
 
I was fighting with a big load as I typed this. 10 minutes or so burning wide open and the stovetop was 650, andirons a dull red, cat probe already at 600 just from the radiated heat. So I close hte bypass... cat climbs 650... 700 then sits.... and drops back to 650. Look outside, billowing smoke.

Hmm.

So I open the damper up again.. Let the stovetop get to 700. Close.. Now the cat climbs to 750 .. 800... sits for 5 minutes then boom 900 950 1050 1100. I close the air in stages down to fully closed and the cat settled into 1250. Nothing but a wisp of steam outside and now the living room is 76F!


Maybe I just am being too cautious and need to get it HOT ?
 
The vermont castings stoves are a different design then other cat stoves - they are a downdraft stove with the cat in a chamber at the back of the stove. The cat intake hood is on the fireback below the bypass damper - any more 3 splits in one of these and the wood is above the cat intake. The cat also has a separate secondary superheated air supply that feeds under the refractory box, behind hte firebox and directly into the cat intake hood. There is no way to block it that I can see.

I do the big loads because it will get you honest 10-12 hr burn times in this thing which is nice for nighttime. I can load after dinner and forget about it till after breakfast.

I agree with you that glowing andirons is not good, but I've never had the griddle over 750 which is the overfire temp per the manual. I wonder if its not so much the firebox temp as the load just needs to burn off more volatiles before engaging the cat. Maybe next time I might try lowering the air a bit with teh damper open and burn a bit longer at 500 or so before shutting the bypass.


One thing I know for sure though from experience with this stove - if that cat probe doesn't rise to 1000 in the beginning of hte cycle its not lighting off right. When it just sits at 700 I get billowing smoke.... On the end of a burn cycle on the other hand as it buns down to coals the cat will still be working at those temps.
 
If you "stall" a cat it's prolly because there was not enough smoke to feed it..I have done it.
I have done it on purpose on night loads to get even a longer burn..it has always came up to cat temp sometime during the night because it will be orange when I check at 6:30 in the morning...2/3-3/4 on cat temp...69-72 in the house...shoulder season..and I don't reload till that night.

Anyways if you want it to light off better with a big load..spread your coals out and let her rip for awhile..but you need enough of them.
Works for me.
 
You might try closing the bypass halfway for a while to try to divert more of the exhaust gases through the catalyst. Since the stove is a downdraft, you need to "encourage" the smoke to follow a path of more resistance.
 
pgmr said:
You might try closing the bypass halfway for a while to try to divert more of the exhaust gases through the catalyst. Since the stove is a downdraft, you need to "encourage" the smoke to follow a path of more resistance.

Unfortunately, this stove doesn't have a halfway setting. All open or all closed on the bypass damper.
 
For those full reloads, it may be best to reload sooner. We get most successful cat launch by loading on a full 3 inch bed of hot coals front to back. Your post "rake the coals to the front" suggests too weak of a coal bed. Then, after torching the new load, after closing the damper, leave the primary lever full open for 5 minutes. Then close the primary lever to 7: o'clock another 5 minutes. Then for a few more minutes slowly nudge the lever to its final long-burn position. This is how we get the most consistent smoke-free reloads with our Encore.
 
Thanks for all the ideas guys... the thoughts on the coal bed might just be my problem.

Its been weird weather here - mild days then going down really sold at night. There are some days I only need one medium load in the morning and then let it simmer on minimum air all day to save the coals. When I reload in the evening I'm starting from a rather small coal base - but I guess my wood is good ;) as I can get the fire going without kindling even hours after the fire died down. Maybe in those situations what I should do is put in a small 2 split load at dinner, let that warm up the house and build a fresh coal base then reload the big night load so I have a better coal base.

I'll try some different methods and keep track of what works and what doesn't.
 
I have discovered that If I shut my bypass almost all the way I can get my combuster hot a lot faster and it smokes a lot less. Since its gotten colder the last couple of days there is no smoke! On downdraft one thing that is important make and maintain a large coal bed mine are 4" minimum.

Good Luck
Pete
 
It is a cumbuster in he back not cat however it is downdraft and also needs to be heated in order to ignight. I am assuming the pr eheat part is simmilar to a cumbustor anyway. They are different from there I believe .

Pete
 
Jeremy - another idea: we notice that when a new load of splits is up against either side air plate (sidewalls), that end of the load almost never gets involved in flame for the initial open-damper torching. With no space for air to ignite that end, all the start-up fire happens at the opposite side. Previous posts here have mentioned leaving at least 1 inch space between splits and firebox walls - for our 2550 we get best relight when the new load is centered in the firebox left-to-right. This is really important when the new load has straight splits and they are packed tightly together ,, no burning occurs between the splits at first so they make no gasses for the cat. I used to think packing the nice straight splits together tightly like a puzzle gave a longer burn ( it does), but it thwarts the cat start-up process. So, maybe center your load and include one gnarly twisted knobby split in each monster load (in front). Thanks for your feedback, we're still trying to figure out this beastie too.. LOL.
 
Interesting observation Gark... that is one other significant difference in how I pack it for a night load that I didn't consider. Will try that next time. I doubt the one less split from centering the load will make that much difference anyway.

In other news - I followed the various advice above and tried a different method tonight. Its been cold all day so the house was cooling at dinner. Still some good coals, but rather than stretch it I put 2 splits in for another couple hours heat. Then I reloaded on a nice good coal bed, raked it even (not to front) - prob a solid 2in of glowing coal. Then I loaded it, fired it off, but when it got to about 500 I reduced the air a bit to slow it down some and burned it a bit longer on bypass to get the load more evenly charred without hitting 600+. At this point the cat prob was reading 700 just from the radiant heat. We are now at 20 minutes since load up.

Close the damper.

BOOM. cat lit off immediately and shot straight to 1050F just like a small daytime load.


Thanks SO MUCH for all the great advice, and next time Ill try Garks idea as well. Glad to know my catalyst is still good!
 
Some more follow up... I have been trying the method Gark mentioned and centering the load even for a full pack and spreading the coals as mentioned above. I'm getting much better results - reliable cat light off every time - even with smaller coal beds - and it seems more controllable. I haven't had the catalyst temp run up past 1500 once since I changed my habits. The one or two small splits less has not made an appreciable difference in the length of an overnight burn.

I feel like I finally have this stove working like its designed to. I can just do a full load a couple times a day and regulate the heat with the thermostat and keep very even temps in the house without the big heat spikes trying to light off a full load.

Thanks again to everyone who gave advice. No matter how much you think you have something figured out there is always room to learn!
 
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