25-PAH Premature Burn Pot Failure - My fault or the burn pots? (2 burn pots in 4 months)

[acammer]

Good morning all. During my last normal clean up I found a major crack had developed in the burn pot of my Timber Ridge 55-TRPAH (Englander 25-PAH). I was pretty frustrated to see this, as this is the second new burn pot this stove has had this season - I bought it as a new/refurb from AM/FM Energy in late November, and replaced the first burn pot 1 month ago almost to the day. The failures are almost exactly the same between both of the failed burn pots - a crack forms between holes in the middle of the pot.

What I'm trying to determine is if there is something I'm doing wrong that's leading to these failures. Let me give a little background on usage. My stove lives in my finished basement, and is responsible for heating the whole 2,100sqft house (with a little help from the propane furnace on really cold days). The stove runs wide open whenever it's under 20*F outside, when it's a little warmer it gets to idle 4-6hrs at night when the thermostat sets it back at 11pm. So far I've burned through about three tons of fuel. I clean the stove every 24-48hrs - this consists of shutting it down, vacuuming up all ash including the ash pan, cleaning the glass, and scrapping out the burn pot. I knock it out against the floor a few times to get any buildup out, then I use a scraper (usually a putty knife and a flat bladed screwdriver) to get any stubborn carbon out. Lastly, I take a small rod (3/16") and work it in and out of each of the holes in the bottom of the pot - the side holes don't usually need any attention. Some times when doing this I notice small flakes of what I assume is buildup (maybe it's metal) come off the bottom of the pot. I'm not aggressive with the scrapping and cleaning of the holes.

I'm at a loss here - I'm not sure what's causing this, but 2 burn pots in 4 months is crazy. The last one made it barely thirty days! I want to see if there are any thoughts out there on this - maybe I'm doing something wrong here. Maybe it's just two bad burn pots in a row. I just know that I need a stove that's gonna run for more than a month without replacing a $70 part over and over.

 

[SmokeyTheBear]

A smidge more air or a smidge less pellets might go a long way towards extinguishing the forge aspects of your burn.

 

[acammer]

A smidge more air or a smidge less pellets might go a long way towards extinguishing the forge aspects of your burn.

Air is maxed - I can definitely trim the fuel back some, but I'm trying to extract maximum heat. It definitely doesn't burn dirty, but I am running as hot as I can get it. It's never over-fired. Book doesn't say you can't run it on high 24/7. Maybe it turns out that it's just not engineered to handle what it's rated for - wouldn't be the first piece of equipment to have that be the case.

 

[SmokeyTheBear]

You need damn near perfect conditions in the air flow department if you are trying to maximize heat output do not send it out the flue.

Pellet stoves can be run to burn pellets or burn pellets and extract heat, sometimes that is not the same thing.

Once you get to the point that you get carbon building up in the burn pot you are operating a forge and frequently sending the heat outside the stove via the flue as the air flow is too fast for the exchanger to have enough time to really get as much heat as possible out of the exhaust stream..

 

[SmokeyTheBear]

I destroyed my first burn pot in a month the second one is still going strong almost 7 years later.

 

[acammer]

You need damn near perfect conditions in the air flow department if you are trying to maximize heat output do not send it out the flue.

Pellet stoves can be run to burn pellets or burn pellets and extract heat, sometimes that is not the same thing.

Once you get to the point that you get carbon building up in the burn pot you are operating a forge and frequently sending the heat outside the stove via the flue as the air flow is to fast for the exchanger to have enough time to really get as much heat as possible out of the exhaust stream..

That all makes sense to me. I've done my tuning with a thermometer mounted to the heat exchanger exhaust that I've kept in the extra same place the entire time I've owned the stove, and compiled some results to determine with which settings I get my best heat. I definitely would allow that I am certainly running past peak efficiency - all my tuning has been in the pursuit of maximum performance as I'm using the stove in it's maximum defined area of coverage at it's maximum output (2,000 sq ft and 25k output BTU). That 25k BTU figure the manufacture gives has to come at around 4lbs/hr of feed, which is essentially with the fuel trim maxed out. I'm not at that point, but I am about half way on the trim (on the highest heat setting) for my routine running which is pretty close. I guess I'm disappointed that in order to get the performance promised by the manufacturer the stove doesn't seem to be equipped to tolerate it. Again, I acknowledge that I'm running the stove towards the outside of the envelope - but I am within the envelope. I haven't made modifications to the stove, I just want the performance promised when I bought the stove, without it self destructing to give it.

 

[acammer]

A good question you might have good insight into is what characteristics of a burn are indicative of a "forge" scenario. Carbon buildup you mentioned, what other clues would reveal this? I assume (and please expand if I'm off or confirm if correct) that when the burn is acting like a forge it creates such high heat in the burn pot area that it is fatiguing the metal, and leads to this type of failure.

 

[SidecarFlip]

A smidge more air or a smidge less pellets might go a long way towards extinguishing the forge aspects of your burn.

Less air. the OP has an oxidizing flame. Very evident by the oval shape of the holes.

 

[SmokeyTheBear]

A good question you might have good insight into is what characteristics of a burn are indicative of a "forge" scenario. Carbon buildup you mentioned, what other clues would reveal this? I assume (and please expand if I'm off or confirm if correct) that when the burn is acting like a forge it creates such high heat in the burn pot area that it is fatiguing the metal, and leads to this type of failure.

Other signs are a glowing burn pot, and the fusing of ash into fully formed clinkers that look like metal. It causes the metal to come under varying levels of expansion at different rates due to temperature differences from one end of the pot to the others which stresses and deforms the burn pot to the point that it creates its own air bypasses and breaks down. These temperatures are met once the carbon (charcoal) actually ignites. The forced air system in the stove virtually ensures this if the the fuel load is too much for the air to eject the ash in time.

 

[acammer]

Less air. the OP has an oxidizing flame. Very evident by the oval shape of the holes.

Less air isn't possible. Let me be more specific - the controller has 9 heat ranges. On heat range 9 the combustion blower runs at full speed irregardless of the air trim. I can't imagine that the stove would be unable to run on it's highest heat setting. I think the photo is a little misleading in that the angle does make some of the holes appear oval-ed. They really are not, here is a secondary angle for comparison. I really appreciate all this input though, I do want to learn every bit that I can here.

 

[SmokeyTheBear]

Less air. the OP has an oxidizing flame. Very evident by the oval shape of the holes.

Actually it depends on the fuel charge he is maxed out on air.

 

[acammer]

Other signs are a glowing burn pot, and the fusing of ash into fully formed clinkers that look like metal. It causes the metal to come under varying levels of expansion at different rates due to temperature differences from one end of the pot to the others which stresses and deforms the burn pot to the point that it creates its own air bypasses and breaks down. These temperatures are met once the carbon (charcoal) actually ignites. The forced air system in the stove virtually ensures this if the the fuel load is too much for the air to eject the ash in time.

For what it's worth I've never had the burn pot glowing hot - I've moved the glowing pellets on the bottom aside once or twice (after giving them a few seconds to stop flaming) and not seen any glow. No metal like clinkers either, just the normal soft brown ones. The pot doesn't load up at my usual trim settings, it'll go for days and days.

 

[SidecarFlip]

Other signs are a glowing burn pot, and the fusing of ash into fully formed clinkers that look like metal. It causes the metal to come under varying levels of expansion at different rates due to temperature differences from one end of the pot to the others which stresses and deforms the burn pot to the point that it creates its own air bypasses and breaks down. These temperatures are met once the carbon (charcoal) actually ignites. The forced air system in the stove virtually ensures this if the the fuel load is too much for the air to eject the ash in time.

In 30 years, I've never found that to be true. It's not forced air anyway, it's negative draft and the combustion air is pulled through the fuel bed causing above the fuel bed gasification. If the combustion air exceeds the rate of feed, the fuel bed burns down to the pot itself and the O2 rich atmosphere causes the metal to oxidize and liberate itself from the parent material. The answer of course is to reduce the combustion air volume a bit, either by reducing the available intake (via draft shutter) or slowing the CA fan a bit. Either metnod works fine.

The combustion air will cool the pot to a certain degree so long as it's not so excessive it's reducing the fuel bed to the pot surface.

 

[SidecarFlip]

Cut yout combustion air down a bit. Thats all you need to do. It might take a bit of trial and error to achieve optimum burn but you are delivering (to the fuel bed) too much CA.

 

[acammer]

Cut yout combustion air down a bit. Thats all you need to do. It might take a bit of trial and error to achieve optimum burn but you are delivering (to the fuel bed) too much CA.

I really don't think it's combustion air - there isn't even a way to reduce it on that heat level (as explained above) and I don't believe that the stove was built with an overly lean condition. I understand the theory of the fuel burning down the burn pot itself and the bottom of the pot itself being exposed to O2 rich air - that isn't the case in this stove. If I open the hopper while running, cutting the auger, and let the flames go out, when I open the door and examine the burn pot there is a floor of glowing pellet fuel, maybe the depth of 1-2 pellets, across the entire bottom of the pot.

I think Smokey's proposed issue of creating a "forge" is more likely, as I've tuned the stove for maximum output and definitely and pushing it as hot as I can with the given available airflow. I can understand that the quality of the burn pot material simply may not be able to take the maximum amount of output that the stove is rated for - that's just very disappointing as I had found this stove was just adequate to meet my heating needs. If it turns out I have to de-tune it in order to keep the burn pot alive, then it's actually not capable of it's advertised rating, and that's just not cool.

I think you may have summed up the issue in the other thread we had going last month on this issue:

Cheap azzed burn pot?

 

[slvrblkk]

You can lower your air by dropping your LBA, but the change will be subtle unless you have it maxed on 9. I know the air increases a bit through the controller with heat level increases but it might reduce it a bit overall. Mike would be able to answer that. What do you currently have it set on?

 

[SidecarFlip]

Curious, is the pot ferrous or low grade stainless?

 

[slvrblkk]

Unless they've changed them recently, they are definitely not stainless....

 

[acammer]

You can lower your air by dropping your LBA, but the change will be subtle unless you have it maxed on 9. I know the air increases a bit through the controller with heat level increases but it might reduce it a bit overall. Mike would be able to answer that. What do you currently have it set on?

I mentioned it above - the LBA has no effect on heat range 9 (or 8). You can trim it to 1 or 9 and the combustion blower runs flat out either way. I've tested this right after the stove comes out of start up, before the convection blower kicks on and you can't hear a thing. That's why I hold to the opinion that this isn't a too much air issue - the stove is (or at least should be) designed to handle the air delivered at even the lowest trim settings.

Speaking of trim settings, I typically run at LFF 5, LBA 4, AOT 1. This yields the hottest clean burn possible on the highest heat setting. The stove actually idles nicely too when the T-stat kicks it down - you would think it would need more air with that much fuel trim but it stays nice and clean. Like I mentioned above, I fully realize this much fueling is past the point of optimum efficiency, but I'm looking for maximum heat output with a maintainable clean burn, even if that means burning more fuel. With those trim settings the stove can run for 48hrs, never come off high, and still have a clean burn when I shut it down to clean out the ash accumulation.

The burn pot is definitely not stainless - I'm thinking if I want to be able to push the heat I'm looking for then I'll need to fabricate a hardier burn pot with better material. Maybe the 25-IP (which is rated for another 10k of output BTU) has a compatible burn pot of better material. Still frustrating that the stove doesn't seem to be able to deliver it's advertised output without burning up the burn pot.

 

[Michael6268]

You can lower combustion air by simply partially blocking the air inlet or OAK with foil tape.

 

[acammer]

Well, I submitted a warranty claim this morning for another burn pot and a request for Englander to contact me with whatever insight they can lend to these ongoing failures. I'll let you guys know if I learn anything further to add to the conversation.

I'm not convinced this is an over-air situation - I'm not burning the fuel bed down to the bottom of the pot, I've never blown the fire out when it's turned down all the way, I run the stove richer than the stock trim so it should be less of a problem than it potentially would be with the stock trim settings(which are significantly leaner). I'm always doing the balancing act of running as much fuel as I can without having the burn go dirty. I don't really have the symptoms of a "forge" that Smokey suggests either, so that leads me to conclude that the burn pot just isn't tough enough to tolerate long, hot burns.

For the sake of testing I re-trimmed the stove to the stove fueling point last night to stock (LFF 1 LBA 4 AOT 1) and kept an eye on the fuel in the burn pot and output temp. Output temp is down about 15-20*F, and the burn pot floor has remained covered with pellets having at least a depth of 1.5 pellets. The room that the stove is in ran at least 1*F cooler as well - that doesn't sound like a big deal but that room serves as a giant plenum of hot air that my cold air return picks up and pushes around the house via the furnace blower. In other words, the air turns over really quick in that room, and thus a 1*F drop there is not insignificant. When it warms up outside it's completely reasonable to run these trims, but when it's real cold like it has been the last several weeks I really need to get every BTU possible from the stove, and trimming up the fuel as much as I can while retaining a clean burn definitely yields more output.

 

[SidecarFlip]

One extra question.... Are you running a humidifier and what is the RH? By this time of year, with heating and no adding oif humidity, it can be drier than the Sahara desert in your house and dry air needs to be hotter for a person to feel warm because your body is aspirating moisture to make up for the dry air and that makes you feel cold.

 

[acammer]

No humidifier here - and I actually have never tested the humidity in this house. I can say that it is by far the least driest house I've ever had - but I'm sure it is still fairly dry. That's something worth thinking about, and I'll keep it in mind.

 

[SidecarFlip]

Well, unless you live in a hermetically sealed house, you are driving the ambient moisture out with artificial heat and even if it was hermetically sealed, opening a door lets the humidity out.

Go buy yourself a cheap RH gage or a sling psychometer if you want to spend some miney and check your RH. I bet you'll be amazed how low it really is.

 

[OhioBurner©]

Funny timing, my burn pot on my PAH just did one of those hole to hole cracks. Though mine appears in much worse shape overall with lots of metal flaked off here and there. Its not metal, its clinkers that look like metal, folks here usually said. Well I'm pretty sure now it was metal. Cause there ain't much metal left now lol.