Hearth.com exclusive! Harman re-designing their burnpot...here's the information

I wish Harman would do something about the rotisserie sound. I think it's different than what is being described here. It is annoying. If I can figure out how to post a video to Youtube, I'll start a different thread.

I am also very interested in this as i also get the rumbling from time to time. Hopefully it will be under warranty

newf lover said:

I wish Harman would do something about the rotisserie sound. I think it's different than what is being described here. It is annoying. If I can figure out how to post a video to Youtube, I'll start a different thread.

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Agree. The rotisserie sound is the worst. It comes from the auger motor, but somehow the structure of the stove amplifies the sound. I had my auger motor in my brand new harman advance swapped out, the new motor is slightly quieter but I still have that low pitched hum every time it feed pellets.

Best way to take a video of this is to have the stove cooled down, and start it from a cold start condition. That way you will only hear the auger motor grinding and you won't have the noisy distribution fan running to mask the noise of the auger.

PJPellet said:

Harman definitely needs to keep working on this burnpot design. I have noticed that the fly ash is black instead of the typical grey-white. So the burn is not as clean as with the original pot. In all honesty I am thinking that I prefer the original pot. I DON"T miss the flutter but that is about the only improvement that I can see at this point. I wanted to pass this information along.

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So, do you think the increased air flow is contributing to the ash being ejected before it burns complete? Typically a new design will over compensate for a particular issue on their hit list. Hard to say. I've worked hard trying to manage the air flow to get good combusion, but also a pleasing flame since it's in our main living area downstairs.

I've come to believe that EVERYTHING has a price, so this is one more instance where that rings true. Surely they'll get it worked out as long as the lines of communication are open. HHT hasn't been known for being to communicative though. Keep us posted and we hope it works out for you now and us down the road.

I agree, your flame does seem to favor the left side...wonder why

Any update on the burnbop redesign? I have been using up some misc. Maines Choice, Stove Chow and Green Supreme bags and interestingly the flutter/woofing came back once I started burning Green Supreme. I only had one bag left and when that was done switched back to Greene Team and the flutter/woofing went away. Must have been a fluke because I don't think it has to do with pellets.... The Green Supreme do make my stove crunch/pop when dumping pellets into the auger out of any other pellet I have tried. I think this has to do with the density of the pellet.

OK, If this new burn pot burns brighter and hotter as described, does that mean it`s putting out more heat and efficiency is increased?
I can see the new design eliminating the rumbling and altering flame characteristics but to significantly increase heat output and efficiency would have to be considered a major break through and something that few if any other makers are able to do.
Harman already is a highly rated stove for heat output and it`s hard to believe a new burn pot design alone is going to be of significance with regard to increased heat .
I`m not trying to pour cold water on what might be a good thing but good pellet stoves are probably at the peak of wood burning efficiency with regards to how many BTU`s can be extracted from a pound of pellets so I`m trying to understand if there really is any significant gains in heat output here.

Here's my 2¢.

Im familiar with exactly the woofing you speak of. It can be annoying as it gives the impression that a truck has pulled into the driveway. Pretty much the only truck that comes up my driveway is a brown box truck with goodies for me. My new +150 HP Mega-flo F5 Tornado air filter is here! Hey, this thing was used by top scientists at NASA!..no..no...its just the pellet stove again.

In 2004 I bought my first P38. It was installed in the basement of my previous home and vented into a masonry chimney and up the center of the house. It DID NOT have an OAK. It made the woofing sound only with one particular brand of pellets. I don't remember which brand they were as I only burned about 10 bags of em. I changed the pellets and the woofing went away. For the rest of the time at that residence I burned FU's, some other Energex pellet, and what I consider to be the holy grail of pellets, Eureka premiums. $187/ton at the time but long since disappeared from the NH area.

Was it the change in pellets? Probably. Could it have been something else and the fact it stooped when I changed pellets was just a coincidence? Possibly, especially with my luck.

That same stove is now installed in the basement of my current home using standard pellet vent pipe and now uses an OAK. In 2 years not once has it made the woofing sound. It's been fed NEWP's exclusively.

Last week I installed a second P38 with an OAK on the main floor. I burned 2 bags of NEWP's and had NO woofing. I experimented with a couple bags of Maine's Choice (good heat but ashy) and immediately got the woofing. I switched to MWP's (great heat, low ash) and also got some woofing. In both cases and as others have reported, the woofing comes and goes depending on the burn rate.

What's the significance of this post?....In the immortal words of Mr. PW Herman...I DON'T KNOW!.....but it sure seems that it's more of a pellet issue, rather than a burn pot design issue. Ok, maybe a bit of both.

Anyway, it's nice to see Harman addressing this issue in an attempt to eliminate it in all situations.

I been burning my 2004 P-38 for 4 years now and have not experienced a woofing. I do get this occasionally and very briefly with my 25pdvc in the rear workshop but it`s not a issue at all.
I used to get it with my Franco Belge oil stove on occasion. Under the right conditions I guess it will happen with other stove brands too.

PJPellet said:

mepellet said:

Any update on the burnbop redesign? I have been using up some misc. Maines Choice, Stove Chow and Green Supreme bags and interestingly the flutter/woofing came back once I started burning Green Supreme. I only had one bag left and when that was done switched back to Greene Team and the flutter/woofing went away. Must have been a fluke because I don't think it has to do with pellets.... The Green Supreme do make my stove crunch/pop when dumping pellets into the auger out of any other pellet I have tried. I think this has to do with the density of the pellet.

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Well, the update is that I am going to put the old burnpot back in the stove this summer. Here's why, the newer design is still in the design phase and therefore not perfected. While the woofing stopped, the burn has gotten dirtier and I just don't like the way the stove burns with the newer burnpot, I would rather have some woofing than what I have now. I spoke with my dealer and he passed along this info to Harman.

I think part of the reason for the burn being different is the fact that the burnpot gasket is not used with this newer design so the whole airflow of the system is thrown outta whack.

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Ok thanks PJPellet. I appreciate the update!

PJPellet said:

I think part of the reason for the burn being different is the fact that the burnpot gasket is not used with this newer design so the whole airflow of the system is thrown outta whack.

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who told you not to put the gasket on the burnpot??

After thinking about this woofing problem some more, I remembered something I did to my older P38 just prior to re-installing it in my basement of my new house. On the intake pipe there is a smal round flapper damper thing about an inch into the pipe which pivots on a small tab at the top. I removed this per a post I read a few years ago. This stove has not made the woofing noise once, regardless of the pellets used, whereas it used to do it occasionally at my old house. It seems to run exactly the same with or without this piece, minus the woofing. My new stove still woofs depending on the fuel used. I have not removed this flapper, assuming Harman still uses it. The dealer installed it and I never looked.

Has anyone else tried this simple mod?

P38X2 said:

After thinking about this woofing problem some more, I remembered something I did to my older P38 just prior to re-installing it in my basement of my new house. On the intake pipe there is a smal round flapper damper thing about an inch into the pipe which pivots on a small tab at the top. I removed this per a post I read a few years ago. This stove has not made the woofing noise once, regardless of the pellets used, whereas it used to do it occasionally at my old house. It seems to run exactly the same with or without this piece, minus the woofing. My new stove still woofs depending on the fuel used. I have not removed this flapper, assuming Harman still uses it. The dealer installed it and I never looked.

Has anyone else tried this simple mod?

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oh gosh......youre talking about the intake damper.....I guess I would NOT reccommend doing this...its there for a specific reason......for one, helps stop backdrafting.....also, is a positive stop in the event of a power failure, stopping possible CO from entering the room where there is no intake air pipe.....so, pretty big safety issue here in removing that damper.......yep, simple, but safe? no.

Point taken, especially if one is not using an OAK and I'm not suggesting anyone do this for reasons stated above. I'm not sure if Harman redesigned this damper on newer stoves though. Mine was a loosely fitting lightweight piece that as far as CO and smoke in the event of a power failure goes, IMO wouldn't make much of a difference at all because of the gap around it. If I recall, it didn't seat against any sort of gasket either. I'm not a stove engineer so I'll stop speculating around Harman's design intentions.

Can anyone NOT using an OAK peek inside their intake WHILE the stove is woofing and see if the damper is in fact fluttering with the woofing? If it is, can you open the damper fully or try and stabilize it using a pencil or something?
If the woofing stops perhaps it needs to be weighted like a boiler damper does. I'm sure Harman already has the design of that area covered but who knows. Seems like it's worth a shot. I'd check it on my stove but its a corner install with minimum clearances and im too old and fat to get in there.

P38X2 said:

Point taken, especially if one is not using an OAK and I'm not suggesting anyone do this for reasons stated above. I'm not sure if Harman redesigned this damper on newer stoves though. Mine was a loosely fitting lightweight piece that as far as CO and smoke in the event of a power failure goes, IMO wouldn't make much of a difference at all because of the gap around it. If I recall, it didn't seat against any sort of gasket either. I'm not a stove engineer so I'll stop speculating around Harman's design intentions.

Can anyone NOT using an OAK peek inside their intake WHILE the stove is woofing and see if the damper is in fact fluttering with the woofing? If it is, can you open the damper fully or try and stabilize it using a pencil or something?
If the woofing stops perhaps it needs to be weighted like a boiler damper does. I'm sure Harman already has the design of that area covered but who knows. Seems like it's worth a shot. I'd check it on my stove but its a corner install with minimum clearances and im too old and fat to get in there.

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cant answer the woofing thing, but can tell you the damper closes with no gasket

I remember reading somewhere that reducing the volume of incoming air also helped the woofing sound with an insert. I'll be darned if I can find it though.

jtakeman said:

I remember reading somewhere that reducing the volume of incoming air also helped the woofing sound with an insert. I'll be darned if I can find it though.

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I also remember reading that.

My main point is that this damper swung extremely easily. Possibly easily enough to start to oscillate CAUSING the woofing noise. It could also be a sympathetic oscillation caused by the woofing, which is in turn caused buy....well, that has yet to be determined I guess. That's why it would be appreciated if someone with access to a non OAK intake could check this out.

PJPellet said:

Hi, in my experimenting with everything I actually bought a new OAK intake and removed the flapper. And sadly that made no difference. I was convinced that it would because as you mentioned above the flapper swings easily and I noticed that it did move in time with the woofing, doing the "sympathetic oscillation" thing. But sadly it made no difference.

Also, while I had the OAK disconnected I ran the stove for a bit for more experimenting and I found that the woofing was MUCH worse with no OAK at all connected.

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well, at least you narrowed down the possible "sympathetic oscillation" theory. Sorry if its been stated, but whats the outlet pipe configuration? Have you tried a "minimal installation" configuration with the outlet (straight out, NOT going upwards)? since nearly all of the air going into the stove comes thru the intake damper, it makes sense that the "woofing" would open and close the damper....but, as we now know due to your observations, its a RESULT of the woofing, rather than the CAUSE of the woofing. Since the combustion fan is a constant speed, it is unlikely to be the cause of the woofing. I think I will put my money on the idiosynchracies of variations in the draft caused by variable weather conditions such as piping, barometric pressure differential, and additionally, and to a much lesser extent, cleanliness of the exhaust systen as well. I guess if were a major design flaw, it would be more common than we are seeing, so the only conclusion I can hypothesize is the aforementioned observation above. I know since several folks posting here do mention this "woofing" it might SEEM common, but, given the literally tens of thousands of units produced each year, and the lack of commonality of this issue being pointed out to dealers and service techs, its a very, very small percentage of the stoves produced. How about elevation issues? Has anyone tried replacing the stock combustion fan blades with one of the "high elevation" combustion fans? Just a thought.

PJPellet said:

Hi, in my experimenting with everything I actually bought a new OAK intake and removed the flapper. And sadly that made no difference. I was convinced that it would because as you mentioned above the flapper swings easily and I noticed that it did move in time with the woofing, doing the "sympathetic oscillation" thing. But sadly it made no difference.

Also, while I had the OAK disconnected I ran the stove for a bit for more experimenting and I found that the woofing was MUCH worse with no OAK at all connected.

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Pjpellet, just to clarify we're talking about the same flapper/damper piece....you are referring to the metal intake damper incorporated into the stove from the factory, correct? You mentioned you bought a new OAK intake and removed the flapper. I want to be sure you aren't referring to an intake mounted on the outside of the house, not unlike a dryer vent, which also has a similar design but with a reversed flapper.

P38X2 said:

Pjpellet, just to clarify we're talking about the same flapper/damper piece....you are referring to the metal intake damper incorporated into the stove from the factory, correct? You mentioned you bought a new OAK intake and removed the flapper. I want to be sure you aren't referring to an intake mounted on the outside of the house, not unlike a dryer vent, which also has a similar design but with a reversed flapper.

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except any and all of the Harman OAK's (theres only 2) have NO dampers in them at all........

In my case, and going back to where I first chimed into the thread, my original installation of my older P38 was in my basement. It had a stove adapter that mated up to 8" stovepipe. There was the adapter, a 90, 4-5' of straight pipe and another 90 which was inserted into a thimble that led into the masonry chimney up the center of the house. It woofed occasionally and I never noticed any correlation with the weather.

Currently this stove is in my basement of my new home and is without the intake damper and has a DIY OAK installed. The exhaust is 4" pellet pipe the whole way. I have the stove adapter into a T cleanout. Above that are 6' of straight pipe, a 90, a 1' piece through the thimble in the concrete wall, another 90 turned upwards to approx 30 degrees and a 2' straight pipe with a turbo cap. Not once has this stove woofed in this particular installation whereas it used to at the other place. The main variables are 1) the new installation, including the OAK and 2) the removal of the damper. Does that necessarily mean that it was the switch in pipe types/lengths that eliminated the woofing? The removal of the damper? The OAK? Unfortunately, not necessarily. However, no other items (various gaskets, etc) previously blamed on causing the woofing on the stove changed.

My new stove on the first floor uses the Harman OAK/exhaust/thimble combo. It's installed with minimum clearances into a corner. The exhaust turns 45 degrees and goes straight out, horizontally. On the end is another turbo cap. It woofs all the time, not bad but enough to get your attention. The only time it didn't woof was the with the inaugural bag of pellets which were NEWP after which I switched to MWP and Maine's Choice. I'll try the NEWP in the next filling.

After Pjpellet's observations, It seems Lousyweather could be accurate with his thoughts although my guess is there are more people than we think listening to and simply tolerating this woofing. After all, it's not flames and sparks shooting out the back. Maybe it has to do with something as simple as the length of exhaust pipe exciting/amplifying the combustion frequency of the pellets. If you've ever used a didgeridoo you'll know exactly what I mean. Another example is the relationship of port diameter/length, box volume and driver specs in a subwoofer enclosure. SubWOOFer.....hmmmm....the irony.