Catalytic Stove Problems

[wood4free]

First winter burning in an Appalachian 52 Bay used as an insert. I really like the stove for the long burn times which usually give 8 hours of meaningful heat (I know it is not a Blaze King!). However, I am experiencing a few problems. Perhaps you CAT experts can diagnose.

1) I get the fire going and close the bypass and shut the air down. Temp climbs, sometimes to 1600 or more. I come back a couple hours later and the probe is down to only 700 with a large amount of charred wood in the stove and not much heat being produced. This has happened numerous times so my only solution when loading the stove is to open the 2 air sliders about 30% to maintain the burning process. This seems to be the sweet spot but I almost always have some flame going which I know is not so good. I'm also concerned about exceeding safe catalytic temperature with the air open 30% when I'm not around.

2) Related to #1 I am finding I have a large amount of coals and charred wood in the stove. I have to assume that my wood is not dry enough but I did split some locust into smaller pieces and the face of the splits measured 15 - 17%.

3) I sometimes have a very difficult time of getting the cat to light off. Occasionally I can get light off at 700 but other times, especially with locust I'm still trying to get the cat to take hold at nearly 1000 degrees and usually it does not go above 1100 once lit. Can the type of wood being used affect the temperature the cat lights off and also how high the cat probe temp goes?

In case this question comes up - my liner is about 22 ft. and I have roxul for a blockoff plate in addition to being attached to the walls of the fireplace around the insert. Blockoff plate seems to be working as there is only a 6 or 7 degree difference in the temperature of brick on the outside of the chimney.

Any suggestions would be most appreciated.

 

[johnstra]

As is so often the case, first rule out the wood. You say it's 15-17%. That was the reading from a freshly split piece? Even if it is, it would be helpful to buy a couple of bundles of known dry wood and check how the stove behaves with that. If it's the same, you can rule out your wood.

It kind of sounds like a cat stall. I would guess marginal wood would be more likely to stall than dry wood. Your stove will have a range of air settings that will work. Below that range it might/will stall.

 

[mellow]

Sorry this one got by me. This sounds like a wood issue, too much moisture is going to cool the cats and lower the temperature or stall them. I usually close the left slider all the way and leave the right one open slightly so their is a little flame in the firebox, in these colder temps you could probably just shut it down all the way.

I personally wouldn't run this this stove without having an insulated liner, that seems to make a world of difference with these cat stoves.

 

[wood4free]

johnstra & mellow, thank you for the responses. As a test I re-split a load of wood and measured 3 points on the face of each split. If my HF moisture meter is accurate, this load of wood measured 15 to 17%. I got the wood burning and shut it down nearly all the way. Cat probe went up to 1400. A half hour later when I checked the probe had fallen to 800. Once again I got the wood burning well and shut the air down. This time the probe got up to 1800. Another half hour or so the probe had dropped to 900.

Unless I open up both air sliders about 30% of the way it seems the wood nearly quits burning after a short period of time. However, I am concerned that I will get too much flame and ruin the cats.

Mellow, my liner is insulated with 1/2" ceramic wool the full length. I will continue to experiment but any other suggestions would be welcome.

 

[Woody Stover]

I'm assuming you bought the stove new and that the cat is only a year old? If so, that cat should keep cranking once it's lit off. Have you noticed any slowing of the draft since you started burning the stove? Is it possible that the chimney cap screen is partially plugged?

 

[Ashful]

I'm not sure I understand the controls on the App.52, as based on a thread between AppalachianStan and Mellow, it seems to have a few controls that mine does not. My cat stove experience is solely my Jotul Firelight 12's, in which the only controls are a cam to open and close the bypass damper (must be fully open or fully closed, no option to leave partially open with my stoves), and the primary air control. Also, my stoves are both downdraft cat's, which seem to perform like no other once lit, but can be hell to achieve light off. The catalyst stays absolutely cold prior to closing the bypass damper, and so in my description below, note that I see zero temp on the catalyst prior to closing the bypass.

My reload procedure on a warm stove is to open the air full before I go to fetch wood, trying to get the coals "excited" again. If coal bed is strong (stove top 300 - 400F), I'll just load big stuff. If coal bed is weak, I'll go back to small splits, get her going good, and then load the big splits. In either case, I run the stove in bypass with primary air open wide, until my flue temp hits 500F. I'll close the primary air half way (thanks rideau), keeping the flue temp in that 500 - 600 F range, while I wait for the stovetop to get into the 550 - 600F range. Once the stovetop hits 550F, and always before it hits 600F, I close the bypass damper. At this time I usually open air back to full (although I often forget... doesn't seem to make a huge difference), and walk away from the stove for 5 - 10 minutes.

Depending on how dry my wood is, and how small the splits are, I'll find one of three things have happened when I come back to the stove 5 - 10 minutes after closing the bypass damper:

1. Good dry wood, smaller splits: cat probe temp will be at 1300F
2. Marginal wood, larger splits: cat probe will be at 750'ish, and hang there for some time, but will slowly climb to 1300F over the next 15 - 60 minutes
3. Wet wood, or very poorly seasoned: cat probe will initially climb (maybe as high as 1000F) after closing bypass, but will then fall back down to 500'ish over the next 5 - 10 minutes

I have found that I must leave air half or full open until the cat probe temp exceeds 1000F. If I turn down the air sooner, the cat will stall, and probe temp will fall.

Now... until several weeks ago, I would have told you that I can turn the primary air down to zero once the cat is cruising above 1000F, and it would just hold. However, I'm finding more recently that doing this in all but the absolutely coldest weather will cause the cat to stall, and I'll come back to a stove with some unburned fuel remaining. This phenomena may have coincided with me bringing the most recent cord of wood up to the house, so it may be related to wood quality. However, I have inspected my cat's, which are only a year old, and they look pretty beat up. I need more time to play around to see if this new phenomena is permanent, and if cat degradation can be blamed.

Based on your description, it sounds like you are having a similar problem. You get the stove going, get the cat lit off, and then you're stalling it. This could be your technique, as it sounds like you're lowering the air all at once, which could stall (or initially overheat) the cat on many stoves. It's also a good way to get some nasty backpuffs. I lower my air to 1/2, then 1/4, then 1/8, then closed, in 5 minute increments... starting only after the cat temp exceeds 1000F. Ruling technique out, you already know what must be done:

1. Inspect flue and cap for clean path.
2. Clean and inspect catalyst condition. You should be able to see thru all cells.
3. Try some known dry wood. Framing lumber is always a good bet for furious catalytic temperatures.

 

[windchaser]

It's been a bit since I had my cat but generally I found once you kick the cat in the key to maximizing your burn time is basically lower the air flow down as low as you can possibly go (within reason) however I always took my time with that...lowering in small increments at a time...as I recall I would need around 20 minutes with the cat on of slowly throttling the air back and then you could leave it for a good long burn....

 

[mellow]

Once I get my cats to 800-1000 I close the damper and turn down the air in stages till I have one slider barely open, the cat will climb to 1500-1600 and stay there for couple hours then gradually come down, after about 8 hours I am usually still at 600-800 on the cat probe.

I wonder if you have a bum set of cats? Or if they have been thermal shocked one to many times?

 

[Ashful]

Inspecting cat's for damage is fun work. I wrote up a little summary of failure modes a while back. Lemme see if I can find it...

Here are the basic failure modes of a cat:

- Temperatures over 1800F will cause the catalyst plating to delaminate from the ceramic. Not an instant-death scenario, but definitely shortens its useful lifetime. This is most often caused by resinous woods (walnut is the one that gives me the most trouble), or loading too many small splits, which off-gas too quickly in the early part of the burn cycle. When you see your cat probe climbing to 1800F, open up your air control, which will allow more of the gasses to be burned in the firebox, reducing the load on your cat. If you're stuck between overheating your stove and overheating your cat, then it's time to open the bypass damper.
- Direct flame impingement can cause the same type of catalyst plating peeling that you see in a classic cat over-temperature scenario.
- Plugging with ash is caused by burning garbage, cardboard, improper firestarters, etc.
- Plugging with creosote is caused by engaging the cat too early, especially burning wet or pitchy woods, such that it's in the smoke path without being in the active (500F+) region, as measured on the cat temperature probe.
- Poisoning is caused by burning many different chemicals, including painted wood, pressure-treated wood, garbage, plastics, lots of galvanized nails, etc.
- Cracking and all mechanical failures are caused by rapid temperature change. Hot to cold (throwing a big load of cold wood in and re-engaging before the steam is sufficiently baked out), or cold to hot (engaging a cold cat during a vigorous burn, causing direct flame impingement on a cold cat.

If I saw a hole thru the middle of my cat, I'd assume thermal shock resulting in cracking and failure, nothing else. I don't think you can get a cat hot enough in a wood stove to actually burn thru ceramic.

 

[wood4free]

Thanks to all that responded with suggestions. On Saturday it was warm enough that I cleaned all the coals and ash out of the stove and let it cool down. I removed the flame shield and exposed the front of the cats. I used a small shop vacuum to remove ash from the front of the cats. Then I reversed the hose and blew air through the cats to the back which I could not see since I didn't want to lower the entire bypass assembly. I did several short pulses and closed the door each time since a ton of dust came out. Upon very close inspection of the cats, I saw a little bit of hairline cracking in each cat. I understand this is normal wear but I doubt that is normal wear for only 3 1/2 months of use with a brand new stove and cats. Hopefully, if the cats fail it will be in the first 3 years so I can get free replacement. After starting the stove back up I noticed the cats were much more responsive and the stove seemed to produce more heat. Still not sure if dusting the cats solves my shutdown problem as that seems to be from a lack of oxygen . to keep combustion going but the cats are lighting off much easier. Later in the week when it is colder I will fill up the stove and see if I can shut it down more than I was able to prior to vacuuming the cats.