PB-105 Burnpot Revisited

Mr._Graybeard · Oct 24, 2013

For comparison purposes, my boiler is direct vented, no OAK. The exhaust vent rises 5.5 feet and has a 9-foot horizontal run to the outside.

I burned about six tons last year -- four tons softwood, the rest hardwood and blends -- and maintained the stove regularly. Firepot scraped every couple days, traps cleaned every week or so, combustion fan checked and leaf blower trick about halfway through the season.

Last year we had a fairly mild fall here, which means the boiler got to cool down a bit during the day. That might mean the burnpot saw some fairly wide temperature swings, especially at the spot closest to the igniter. I have had the minimum temp dial set at 140 -- I think I'm going to raise it a bit, to 150 (max is at 160 right now). When winter really sets in I'll bump it to 180/160.

ScotL · Oct 25, 2013

Centurion said:
Hey Scot, what are you using as a vent, a thru the wall or a full size chimney?

Mine is through the cement wall. It's about 5 feet vertical, then about 6 feet horizontal - going through the cement at around the 4 foot mark, then another 4 to 5 feet vertical outside with a rain cap. All in 4".

Also, I recently attached a flexible 4" line with a 4" to 3" reducer at the air intake. I had to go with 4" because it was starving for air with 3" (too long a run) and even with 4 I partially unhook it during the coldest parts of winter because it will sound like a helicopter when it doesn't get enough oxygen. The only reason I added the semi-OAK was because I don't always clean it regularly and this way the smoke from a bad ignition gets, mostly, blown outside.

Centurion · Oct 25, 2013

iceguy4 said:
wow
I stand corrected There HAS to be a common denominator.. My signature pretty much sums up my usage 7 + tons pellets from mid December to end of season. My burn pot looks un changed in any significant way. my vent goes up 5' ...90° ...then straight out 5'...most of the season OAK.. I have a pressure igniter. I'm very curious . Maybe if everyone posts their setup, it will stand out. Kevrev,, how does your setup compare to Mr. Graybeard's setup.?
Also Centurion and I have the newer style (Pic's in https://www.hearth.com/talk/threads/harman-burnpot-just-got-a-new-floating-floor-style-pics.115575/ thread. Centurion has installed his and I was gonna...but I'm not gonna rush.. I'm kinda thinking..."if it aint broke, don't fix it"...or I remember another saying...US Military..."If it aint broke, fix it till it is!"

You are correct Ice, there has to be a common denominator for those folks that have this problem. I've wondered if it could be related to the draft that one has from the chimney. I kind of look at the burnpot issue like a blacksmith with his bellows, fire and the steel. You have a very hot fire and coals inside the burnpot and you have a draft entering the firepot. More draft more heat, more heat more metal deflection, more deflection more metal fatigue. I would say that it also greatly affects the temper of the steel as well. When you look at the burnpot you can see that the coals are white hot. I have a strong draft from my chimney, which I try to control, but that is why I was thinking that this may be the issue. Apparently it is not that simple though as there seems to be folks out there with this issue and have just a thru-the-wall vent so the only draft they will have is from the draft fan. Whatever the issue is I hope this new burnpot is the answer

ScotL · Oct 25, 2013

I've recently been working with some large biomass combustor designers. One thing I remember them saying is the moving grates they use are specially designed with a specific chrome content. It was important enough that they mentioned it twice but there was so much other information that I don't remember the exact metallurgy now.

With all the air holes in the new burnpots, it looks like they've determined that the problem is not enough airflow to pull the heat up and away from the steel.

iceguy4 · Oct 25, 2013

ScotL said:
I've recently been working with some large biomass combustor designers. One thing I remember them saying is the moving grates they use are specially designed with a specific chrome content. It was important enough that they mentioned it twice but there was so much other information that I don't remember the exact metallurgy now.

With all the air holes in the new burnpots, it looks like they've determined that the problem is not enough airflow to pull the heat up and away from the steel.

I agree scott...Harman has added extra holes. Could it be they are trying to lessen the velocity of the air at that point(where the bubble forms)? Personally, I think its is about the all mighty $$$ and they are using a lesser quality metal for the burn pots.

iceguy4 · Oct 25, 2013

Centurion said:
You are correct Ice, there has to be a common denominator

I found the common denominator! common denominator is.....drum roll please.....If you have a PB 105, your GONNA have burn pot problems. Just discovered a bubble in my burn pot. :mad:

Gonna switch out my burnpot today and fix my old one. I'm very unhappy. Now my bulk feeder likes to make sawdust outa the pellets...this morning I wake up to a stove not burning...7 blinks (no such thing ...BUT I can fu%^$ing count) :mad:

I'm selling my new accentra ( http://albany.craigslist.org/app/4150424724.html ) I am not at all happy with my stove or Harman. I'll pull this POS out and move south. I don't need this aggravation.. did I say I'm not happy?

Mr._Graybeard · Oct 25, 2013

iceguy4 said:
Personally, I think its is about the all mighty $$$ and they are using a lesser quality metal for the burn pots.

This is certainly true. I can't blame them too much -- nobody overengineers anything anymore. I like the idea you have about rebuilding a pot with heat-resistant steel ... but I'll wait until I have to pay for one.

Sorry to hear about your burnpot (and other pellet-burner problems).

ScotL · Oct 25, 2013

I'm going to have to keep a closer eye on mine now.
Do you know what you're going to use to try and fix it? 310 stainless?

wil lanfear · Oct 25, 2013

Common sense tells me that the alloy being used to make these burnpots doesn't have a heat resistance value high enough for the heat generated in the combustion area, no stainless steel alloy does. I mentioned this to my dealer, I've mentioned this to the Harman folks when they came and looked at my boiler, I believe they are trying to find a less costly answer rather than using a alloy such as in the links below.

http://www.sandmeyersteel.com/A600.html

http://www.onlinemetals.com/merchant.cfm?id=880&step=2&top_cat=131

Hey Ice, If you are replacing the burn pot for the first time consider yourself lucky, I've replaced mine way over 20 times, I've lost count. IMHO, I think Harman is getting closer to resolving the burnpot issue but I'm not sure if the stainless alloy that they are using will withstand the heat for the long period of time. (years)

ScotL · Oct 25, 2013

310 stainless is rated for 1150C. http://www.azom.com/article.aspx?ArticleID=966

There's always tungsten. http://www.azom.com/article.aspx?ArticleID=1201
I can't imagine how difficult that must be to work with - and expensive.

iceguy4 · Oct 25, 2013

replaced my burn pot today. Old pot had 124 holes...new one has 140+ ...not including the sides. The holes look bigger too

Mr._Graybeard · Oct 26, 2013

Interesting to see that they built the cracks in this design.

Former Farmer · Nov 2, 2013

Picked up a new style burnpot from my dealer today and installed it.

I noticed on the box it said 309 stainless.

Off of AK Steel's website :
"These materials are generally considered heat-resisting alloys. Their destructive scaling temperature
is about 2000 °F (1093 °C). They exhibit good scaling resistance in both continuous and intermittent
service, but the alloys should not be used above 1800 °F (982 °C) for intermittent service."

Former Farmer · Nov 2, 2013

Here is a copy of the service bulletin from Harman that came with the burnpot.

Mr._Graybeard · Nov 2, 2013

Former Farmer said:
Here is a copy of the service bulletin from Harman that came with the burnpot.

View attachment 116549

Thanks for posting! I saved a copy of this.

Go Pack!

exoilburner · Nov 3, 2013

Former Farmer said:
Here is a copy of the service bulletin from Harman that came with the burnpot.

View attachment 116549

Awesome! Thanks again. Very helpful.

Pellet_Dog · Nov 5, 2013

Former Farmer said:
Here is a copy of the service bulletin from Harman that came with the burnpot.

View attachment 116549

Thanks for the literature! It's nice to see one can still use the new burnpot with cartridge ignitors to avoid the expensive upgrade to the forced air inline heater!

exoilburner · Nov 9, 2013

Former Farmer said:
Here is a copy of the service bulletin from Harman that came with the burnpot.

View attachment 116549

Harmon just sent me a replacement burn pot. But they sent old original design. Showed a copy of Former Farmer's service bulleting in to my dealer and now they are sending a new design burn pot to replace the old one.

Thanks again Former Farmer. You were a big help here. But I that is what this forum is all about. What a gold mine of information. So thanks to webbie too.

iceguy4 · Nov 10, 2013

exoilburner said:
Harmon just sent me a replacement burn pot. But they sent old original design. Showed a copy of Former Farmer's service bulleting in to my dealer and now they are sending a new design burn pot to replace the old one.

Thanks again Former Farmer. You were a big help here. But I that is what this forum is all about. What a gold mine of information. So thanks to webbie too.

Well I changed my setup because my "Greene Supremes " sometimes will have problems lighting (smokey over feed) rather then to mess with dip switches I chose this setup.

First I installed a 24 ' "dump zone"
second, I switched to "manual ignition"
third, hooked up "outside air temp sensor"(my thought ...in warmer weather , boiler slowing down at lower temp will give more "cushion" before over temp)
As of last night it worked perfectly... (it was rather warm out too)

As for my burnpot, , just maybe the lack of "heat cool" cycles will help....
Thoughts?

mousenut · Nov 10, 2013

I scrape my burnpot when the hopper gets under 40lbs, every few days. After thirty or so bags on my new burnpot, it is already forming a bubble. I think I will take a copy of the bulletin to the dealer and see what they have to say. This was the burnpot they gave me in September, same look as the old one just has a stainless top I guess.

iceguy4 · Nov 10, 2013

mousenut said:
I scrape my burnpot when the hopper gets under 40lbs, every few days. After thirty or so bags on my new burnpot, it is already forming a bubble. I think I will take a copy of the bulletin to the dealer and see what they have to say. This was the burnpot they gave me in September, same look as the old one just has a stainless top I guess.

Thank god we have this forum...with out,...there is no doubt in my mind , dealers would be saying " never herd of this" , "you're doing something wrong" ,"you're pushing your stove too hard"...etc.

exoilburner · Nov 18, 2013

Former Farmer said:
Here is a copy of the service bulletin from Harman that came with the burnpot.

View attachment 116549

Just received the new design burn pot and am doing the install myself.

FORMER FARMER: did you do your new burnpot install or watch them install it? The new electric igniter holder & Ceramic insert is really a pain to install. I had to enlongate the mounting holes in the holder to get the new ceramic insert in place.
When I put a new igniter in the holder it's fins were hard against the holder and burn pot. I have seen in another post that this condition causes a heat sink on the igniter, lowers it's temp. and makes ignition long and difficult. I modified the holder so the igniter fins were not touching anything. With the old igniter holder I used to be able to change the igniter thru the burnpot access plate. With this new set-up I'll have to remove the burn pot to change the igniter.

Former Farmer · Nov 18, 2013

I didn't have any problems installing mine. I DID NOT use the ceramic insert. Did not see the need to use it as it would have been a tight fit. I can still replace my finned igniter without having to remove the burn pot.

Centurion · Nov 18, 2013

You would only use the ceramic insulator if you were using a pressure ignition system. As you are still using the fin igniter you can disregard the ceramic insulator.

wantageNJryan · Nov 18, 2013

How important is that insulator?? I have another thread called "creosote" which has my newbie pb105 issue but another is see is that ceramic is flaking apart !!!

ease excuse the creosote....thats a whole other story which i hope to be getting a handle on.........

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