Why does my stove sound like a subwoofer? Low frequency vibes... Help!

[lbcynya]

Been chasing an annoying issue with my Harman XXV (born in 2008). Once I get this handled, I'll be able to sit back and enjoy the heat... Stove continually sounds like a helicopter is flying over the house, but the frequency is about twice as fast. Flame flickers at the same frequency, almost acts like a strobe light... Very unsettling.

• Well insulated finished basement install
• Happened since day 1
• Selkirk DT Pipe (did it with Simpson too)
• OAK
• Up and out install - 5' up, then out
• Round flame guide
• Seems to happen at medium/high burn rates
• Happens with all brands of pellets
• Happens with or without OAK attached
• Hopper gaskets seem well in place - I used aluminum tape on the inside joints of the hopper, no change
• Door gasket and hopper lid gasket are fine
• Vacuum pressure inside the stove is pretty high - .6" with the draft voltage adjustment as low as it will go
• Restricting intake air helps, but don't want the flame to get lazy, currently 50% of air intake is covered, burned fine with 65% of intake covered (maybe a little lazy)
• Intake flapper moves free, doesn't appear to be contributing to sound

Drives my wife nuts and I'm not far behind... Please help me make this issue go away. Thanks in advance for your contribution!

 

[Lineman30]

Mine is doing the exact thing!! It only happens when hopper is less than half full. I just recently put the crossover tube kit thinking that would cure it. It did do away with the smoke in the hopper. It drives me crazy also. At least I'm not the only one w/ this problem

 

[mepellet]

I noticed the same type of thing once a few weeks ago! I didn't think too much of it because it only lasted for a few seconds. I will keep an eye on it so see if it happens again. Its a P61A and was installed 2 months ago.

 

[Delta-T]

i would have guessed air intake is "chugging" except that you said it does it with or without it attached. any chance there is some interference on the outlet (electrical) that is causing the combustion blower to have some pulses? restricting the air intake will increase your negative pressure environment, and add strain to the combustion motor in the long run.

 

[Utilitrack]

I had a similar low frequency vibration last season that has gone away since throughly cleaning both fans, probably unrelated but worth checking into. Happening since day 1, did you call the dealer?

 

[lbcynya]

i would have guessed air intake is "chugging" except that you said it does it with or without it attached. any chance there is some interference on the outlet (electrical) that is causing the combustion blower to have some pulses? restricting the air intake will increase your negative pressure environment, and add strain to the combustion motor in the long run.

No electrical issues and the pulse is far more rapid that an fan oscillation could produce, maybe 10-20 Hz.

Restricting Air - I know, double-edged sword. I already have quite a bit of negative in my basement, so it's like my air velocity is supercharged. Flame is wicked angry unless I restrict flow, low frequency vibes are louder... Using 4" pipe with a EVL of about 12. I thought about restricting exhaust, but back pressure isn't any better, is it? Smoky suggested this could cause the motor to get heat soaked, but, since Harman's are controlled by the ESP, the stove wouldn't allow it to get any hotter than it normally would... Restricting flow seems to be more risky since I don't want to create a fly ash catcher and plug up the pipe...

I had a similar low frequency vibration last season that has gone away since throughly cleaning both fans, probably unrelated but worth checking into. Happening since day 1, did you call the dealer?

Installer said he was "tone deaf" so no help there. It's here or HHT... Fans are spotless, chimney is new. I really thought it was a bottom/top hopper gasket, but that's proving false (hopper lid seal is tight). You can see the noise in the flame, so it has to be an air management issue, but I'm wondering if too much negative stove pressure is causing air to bypass something. If that were the case, blocking the intake wouldn't help, it would hurt. Restricting flow does tone it down a bit, but not much.

 

[Lineman30]

I know you probably read my post but did you noticed it at certain levels in the hopper? Like I stated if it's full is a nice flame as it's half or below it's a violent flame with lots of echo tones. It might have to do with negative pressure. Also, sometimes mine does it more violently as the auger is cycling. I've also adjusted the draft up and down and no change. Also, if I sightly release some tension on the door latch it helps it. My pipe run is horizontal with a 45 and 18 inch run

 

[dsnedegar3]

I have a Quadrafire and if after cleaning I don't align the baffle incorrectly, I get that type of low frequency vibration. Typically it happens when I've left more of a gap on one side of the baffle that the other side of stove. Not sure if this makes sense if you have a Harman or other brand.

 

[lbcynya]

I know you probably read my post but did you noticed it at certain levels in the hopper? Like I stated if it's full is a nice flame as it's half or below it's a violent flame with lots of echo tones. It might have to do with negative pressure. Also, sometimes mine does it more violently as the auger is cycling. I've also adjusted the draft up and down and no change. My pipe run is horizontal with a 45 and 18 inch run

Yes, I noticed your hopper level observation. I haven't correlated that yet, but I will. Cracking the hopper lid ever so slightly makes it stop which is why I thought one of the internal hopper seals was leaking causing the rapid flutter and resulting noise. This additional air makes the flame angry again, but that was with an almost empty hopper.

I have a Quadrafire and if after cleaning I don't align the baffle correctly, I get that type of low frequency vibration. Typically it happens when I've left more of a gap on one side of the baffle that the other side of stove. Not sure if this makes sense if you have a Harman or other brand.

Don't think we have anything like that, but my buddies Quad did make an odd sound (almost more like flatulence) when starting up...I'll let him know...

 

[DexterDay]

Seems to be pressure differential. My Woodstove has done this when reloading or starting a fire. If the door is not shut tight, then there is an air leak and it "back-puffs" which makes a great deal of noise and the flame jumps up and down. But this only happens when the dryer is running.

Dont know if that helps much. But I would check all gaskets. A small leak would cause the pressure differential needed. Dont know if you would call it back-puffing on a pellet stove. But I get the Whoomf-Whoomf-Whoomf (1 second intervals).

 

[lbcynya]

Seems to be pressure differential. My Woodstove has done this when reloading or starting a fire. If the door is not shut tight, then there is an air leak and it "back-puffs" which makes a great deal of noise and the flame jumps up and down. But this only happens when the dryer is running.

Dont know if that helps much. But I would check all gaskets. A small leak would cause the pressure differential needed. Dont know if you would call it back-puffing on a pellet stove. But I get the Whoomf-Whoomf-Whoomf (1 second intervals).

Yes, I caught that when I searched the threads for "Woofing or Whoofing". Frequency on this is 10-20 times per second, so something is making the air vibrate... Another thread during that search pointed to the door seal and the dealer replaced the entire door with no luck. Door seals tight, but I'll do the $ bill test to eliminate that from contention. Although I can't see that gasket causing vibration vs. a smooth consistent leak. Door seals normally cause build up on the glass and laziness. Since the gaskets for the hopper are foam, that would seem to be more logical that they could vibrate or flutter, but I've all but eliminated that. Frustrating.

 

[heat seeker]

You could try opening a nearby window or door to the outside. That would eliminate any pressure differential issues.

It just might be that the length of the exhaust pipe is just right so as to cause resonance, just like blowing across a soda bottle, or a pipe organ pipe. If there's an easy way to change the length of the pipe temporarily, you could try that. Take off (or add) at least a couple of feet or more and see what happens.

 

[lbcynya]

You could try opening a nearby window or door to the outside. That would eliminate any pressure differential issues.

Good call. Will at least see if the basement pressure is contributing to the problem...

It just might be that the length of the exhaust pipe is just right so as to cause resonance, just like blowing across a soda bottle, or a pipe organ pipe. If there's an easy way to change the length of the pipe temporarily, you could try that. Take off (or add) at least a couple of feet or more and see what happens.

Hard to say. I did have a 36" horizontal piece through the wall and replaced that with a 24" piece which resulted in no noticeable difference. No chance on changing length further since I had to completely redo what the professionals attempted the first 2 times. Problem was consistent throughout.

 

[mepellet]

I am noticing this now. Running in stove temp and I recently turned up the level to 5. Seems to be calming down a bit now. It does only seem to do it during/immediately after the auger feeds pellets. I'm going to be contacting my stove shop in the next day or two so I'll ask them about it either then or when they come out to replace the pad. I'm still waiting on the hearth pad swap for the ember protection pad that they sold me which didn't meet Harman's requirements.

 

[mepellet]

Just ever so slightly opened the ash pan drawer (lifted the lever and slowly cracked the door open so there was BARELY a crack in it and noticed the booming sound. Maybe there is a slight leak around a gasket somewhere? I do notice that when the stove is starting there is a quiet whistle. Haven't been able to pinpoint where it is coming from but I wonder if it is where the first streak appears on my glass.......

 

[lbcynya]

Hmmmm, full hopper, flame seems to be acting pretty normal. Some fluttering, some rumbling, but that's what I would expect from a forced draft combustion system... Still early, but there seems to be some merit to the hopper level and the strong, loud flame flutter.

Starting to make me wonder if pellet hopper volume could impact air flow... It's the only thing that changes over a period of time and it is an integral portion of the low pressure system. Still early...

 

[gfreek]

When I have a medium to large flame I can feel the floor rumble in tune with flame flutter on my Harman P38. Never noticed hopper level, but will...

 

[mepellet]

Seems like there are a few people ho have this problem. Is it anything to be worried about? Or is it causing any damage?

 

[lbcynya]

Seems like there are a few people ho have this problem. Is it anything to be worried about? Or is it causing any damage?

Naaa, just an annoying issue that might or might not be able to be overcome. Ultimately, fixing or minimizing the issue is my focus.

 

[mepellet]

Seems like there are a few people ho have this problem. Is it anything to be worried about? Or is it causing any damage?

Naaa, just an annoying issue that might or might not be able to be overcome. Ultimately, fixing or minimizing the issue is my focus.

Good to hear. But yea let's try to figure out how to overcome this annoyance!

 

[Lineman30]

Hmmmm, full hopper, flame seems to be acting pretty normal. Some fluttering, some rumbling, but that's what I would expect from a forced draft combustion system... Still early, but there seems to be some merit to the hopper level and the strong, loud flame flutter.

Starting to make me wonder if pellet hopper volume could impact air flow... It's the only thing that changes over a period of time and it is an integral portion of the low pressure system. Still early...

I really think it has to do with the volume of pellets in the hopper. When i got home from work, I had little more than half full and as the evening has gone the symptoms have evolved and its about half full. I know when its at low idle there is nothing but when its at med height, it does it. When its at full bore heat there is really no symptoms.

 

[lbcynya]

I know when its at low idle there is nothing but when its at med height, it does it. When its at full bore heat there is really no symptoms.

Exactly! The flame vibrates vigorously, causing the subwoofer sound. I can literally hear it upstairs. Low frequencies are tough that way.

I also find it interesting that this is not a characteristic of one particular Harman model, seems consistent across the line.

I am noticing this now. Running in stove temp and I recently turned up the level to 5. Seems to be calming down a bit now.

Yes, stove temp, mid flame seems to be the worst. Room temp seems to vary more where stove temp stays in the sweet spot for the vibrating flame..

 

[Lineman30]

I know when its at low idle there is nothing but when its at med height, it does it. When its at full bore heat there is really no symptoms.

Exactly! The flame vibrates vigorously, causing the subwoofer sound. I can literally hear it upstairs. Low frequencies are tough that way.

I also find it interesting that this is not a characteristic of one particular Harman model, seems consistent across the line.

Yes, i can hear it on the other end of my home. Its just annoying!! Wish there was a solution!!

 

[GIPPER]

I found that when I used a lesser grade pellet I had this problem with my Qwad-castille stove.I thought the Harmans could burn just about any kind of pellets.I only burn okies,barefoots,somersets,greenteams,hamers,etc.Hope this helps!

 

[76brian]

I know you said it does it with OAK on or off, but I'm putting this out there anyways... I installed the OAK on my P43 last night, I used 3" sheet metal duct, like furnace duct but smaller (Home Depot OAK for $8, better than $100+). The duct I picked up was in 2 pieces, one was 3ft long, the other was an adjustable angled piece that was only 12".

I installed it with the stove running. I put the 12" piece at the stove side of things and as soon as I did that I noticed the same symptom you described. I connected the longer piece that goes through the wall, and it stopped... took it off again, it started. It only happened with that 12" piece attached to the back of the stove, still taking air from inside the house, but just 12" further away from the stove. Strange.

The hopper was nearly empty, so I filled it and tried it again... no fluttering with OAK on or off, or the 12" piece on or off. Consistent.

This 12" piece I'm talking about is an adjustable elbow, so the air going through it gets diverted a bit and probably creates some wicked air turbulence going into the combustion chamber. The extra air volume in the nearly empty hopper probably amplifies it. Just a theory, I dunno.

So that's what I have observed, I don't have any solution but hopefully the extra observation helps with a diagnosis.

Is there any way you can change an angle or a length in your OAK to see if that quietens it? I assume you probably don't run it with the OAK off anyways.

Coincidentally, I also get the faint whistle sound on initial flame as mepellet described, but it's barely there and goes away rather quickly. I haven't tried to see if it does this with the OAK also, but it does do it with a full hopper.