Loud Humming Noise - Napoleon HDX35 DV Gas Fireplace

[johnfluevogs]

Hi all - first time posting! I replaced an old Martin wood burning fireplace with a Napoleon HDX35 Direct Vent Gas Fireplace. I did the demo and framing, but had a local chimney/fireplace installer supply the co-axial venting and install the fireplace. The unit is installed on the first floor in a chase with 4x7 venting straight up through the top of the chase. The chase height is somewhere around 20'. I believe the installer used Amerivent Direct Vent 4x7 pipe with a vertical cap. The space

Everything seems to be working great, except about 5-7 minutes after the unit is turned on a humming or buzzing noise starts quietly and gets progressively louder. It may be equivalent to the decibels of a blower or fan; however, this unit does not have a blower or fan. Additionally, the noise continues until the unit is turned off and allowed to cool. Said differently, the noise continues after the unit is turned completely off - even the pilot. Finally, the noise stops immediately if you remove the glass front panel. It seems to me the firebox is under negative pressure and the humming/buzzing noise is generated by air being drawn into the firebox - possibly through the rope gasket around the door. All that said, the unit appears to be burring correctly. The installed visited today and confirmed everything appears to be in proper working order, but was stumped by the noise.

Any ideas?

 

[KeithO]

https://napoleonproducts.com/downloads/fireplaces/manuals/W415-1434.pdf

Page 45, section 9.1 of the manual references a restriction kit for vertical vents. Do you know if one was used in your install ? Could try to find the manual for that kit to see what instructions are provided with the kit.

 

[wooduser]

https://napoleonproducts.com/downloads/fireplaces/manuals/W415-1434.pdf

Page 45, section 9.1 of the manual references a restriction kit for vertical vents. Do you know if one was used in your install ? Could try to find the manual for that kit to see what instructions are provided with the kit.

My compliments to my friend Keith O, who looks like he has put his finger on a likely solution to the problem at hand.

The problem seems to be described in detail on page 16 of the installation manual in the graph showing acceptable and required horizontal and vertical vent runs for proper fireplace operation.

The maximum vertical rise recommended is twenty feet, but that requires a horizontal run of about six feet as I read the chart in the installation manual. Since John's installation apparently is all vertical, that suggests that the draft is excessive and is a likely cause of the problem described.


Just as an example, the illustration graph in the installation manual; prohibits the installation of a twenty foot vent rise unless the six foot horizontal run is included. The vent restrictor specifications might modify that, or might not. A manufacturer's tech rep would hopefully have the experience to know how to vent the system you have so that it will work properly.

I agree with Keith O that getting the manual on the vent restrictor to see what it has to say is a good idea and a good start. It might approve just what you need to do.

And you should be able to vastly impress the dealer from whom you bought the fireplace and the installer by coming up with what is likely a terrific solution to what was really a botched installation!


I think Keith O should be awarded ***** for his diagnosis and suggestions!

 

[johnfluevogs]

KeithO - I too stumbled across section 9.1 in the manual, but due to lack of experience, did not want to "lead the witness" and influence any replies. Section 9.1 refers to flames that "appear very active." The flames appear "normal" to my installer. Perhaps you can explain better what the manual is referring to when they say "very active". For context, they are not lifting from the burner and have appear to have normal coloringMeanwhile, I will attempt to track down documentation/instructions for the restrictor.

wooduser - I studied the venting requirements prior to installation and arrived at a different conclusion than you - maybe I am interpreting the manual incorrectly. I concluded that the maximum vertical rise with NO horizontal run was 40' based on the venting arrangement on page 15 of the manual - which applies to scenarios where the horizontal run in less than the vertical run (H)<(V).

In contrast, the venting arrangement described on page 16 of the manual is for scenarios where the horizontal run is greater than the vertical run (H)>(V). Since my run in nearly 100% vertical (with the exception of a small offset), I concluded the scenario described on page 16 didn't apply to my installation. Any thoughts?

Thank you both for your replies!

 

[KeithO]

When I installed my Pacific Energy T5 wood stove with 8' of stove pipe followed by 10' of class A in the attic and poking out the roof, it had so much draft in cold weather that even after adding a flue damper in the stove pipe the stove intake would whistle when fully closed.

Gas stoves are probably more sensitive to high draft and usually lack any air intake control and draft is the only thing still active when you shut the stove off. It does not surprise me that you would have excessive draft with such a long vertical run. Some stoves have a built in damper that a tech can adjust but in your case you have to buy the restrictor kit to get that functionality. Getting the draft reduced will probably solve your issue.

 

[wooduser]

Gas stoves are probably more sensitive to high draft and usually lack any air intake control and draft is the only thing still active when you shut the stove off. It does not surprise me that you would have excessive draft with such a long vertical run. Some stoves have a built in damper that a tech can adjust but in your case you have to buy the restrictor kit to get that functionality. Getting the draft reduced will probably solve your issue.

My guess is that Keith O will be proven to be correct, but you had you own theory of how to interpret the graph, and perhaps you are correct!

This suggests that someone who is an Xpert in installing these stoves needs to be consulted on the right way to do it. Stove manufacturers usually have tech reps who are those experienced experts with their own stoves. You dealer may be able to tell you how to contact a company tech rep or you can try calling the manufacturer directly.

Even though the flames aren't visibly disturbed, the noise you describe is likely to be caused by excessive draft. The graph supports that conclusion for me, and so does the availability of the restrictor. But that doesn't mean I'm correct!

 

[johnfluevogs]

Unfortunately, the techs in the area are not as helpful as one would like, and Napoleon refuses to "troubleshoot" with the homeowner.

This evening I restricted the draft by blocking 25-30% of the chimney opening in the firebox - without success. The noise was differnt but it was still very present. I will continue to experiment with restricting the draft to see if I can eliminate the noise.

Thank you all for the help!

 

[KeithO]

If it was me I would remove a section of pipe above the stove and try to install a flue damper in just the inner pipe. The great thing with a flue damper is that you can open it to light the stove and close it after a few min. It would not be a standard damper install because no-one makes a damper for DV flue pipe.

I had a look for the vent restrictor and it seems to be an annulus which blocks flow on the fresh air side and not the flue side. It does not seem to be adjustable either.

 

[wooduser]

<<If it was me I would remove a section of pipe above the stove and try to install a flue damper in just the inner pipe. >.

You don't want to butch u[p your equipment by doing modifications not approved by the manufacturer.. You void your warranty and create unknown hazards in the equipment.


<<I had a look for the vent restrictor and it seems to be an annulus which blocks flow on the fresh air side and not the flue side. It does not seem to be adjustable either.

Did it have information on how it might extend or modify the venting table in the installation manual?

 

[KeithO]

I could not search for the restrictor on the manufacturers website, or else I may have found a manual for it. Looks like you need to be a dealer to get access. The listings were on Amazon and google, some selling at Walmart....

 

[johnfluevogs]

I installed the napoleon restrictor kit and no change. The humming noise is still very present. Therefore, I am left to conclude my humming noise is not caused by excessive draft.

I am left to conclude there is a leak in the "firebox;" however, I'm not sure where to begin. Any ideas?

 

[Millbilly]

Check for heat shields and metal tags that vibrate as the firebox heats up. It's weird since there aren't really any moving parts but I've seen it just from the stove heating up.

 

[johnfluevogs]

Thanks Millbilly...I have studied the unit over and cannot locate any heat shield or tag. The humming noise may be caused by some vibration; however, I have been unable to locate the source of the vibration. When I feel around, I do not feel any vibration - truly bizarre.

 

[KeithO]

I cant open the file attachment in your post where you installed the restrictor. Could you check that ? Did it go down by the fireplace or up on top of the flue ? Im personally sceptical of the effectiveness of a restriction on the intake air when the cause is too much draft caused by the flue section ????

Now just to be fair, I had a Morso wood burner, a beautiful cast stove with a built in cast iron grate with an ash tray below it. The ash tray had its own door with a latch. If you were having any difficulty with a new fire, you could crack the ash pan door and feed the fire with air from below the grate. If I opened the door, within about 30 seconds, air would be rushing in at such a rate that the whole chimney and stove would go into resonance and make a very loud "booming sound" something like a chimney fire. It was very scary.

I think you have a pretty big air leak somewhere. It could be between the fireplace and the first length of pipe, because that wiuld be a worst case for highest draft, but it could also be higher up in the system. Especially if it is with the inner pipe not overlapping properly, the internal draft of the inner could suck intake air which is coming down the outer annulus back out the central pipe, so it would not involve anything at the stove at that point. The little supports that space the inner from the outer are not very strong and could rattle a little. Especially if the inners are not overlapping in the first place....

 

[johnfluevogs]

KeithO - Thank you. The Technical Service Rep @ Napoleon did ask about the connection between the flue pipe and the fireplace. I explained it was installed per the manual specifications with the correct sealant. Could it require more sealant? Possibly, but nothing about the noise suggests it is coming from the flue pipe or that connection.

My untrained ear puts the sound in the fireplace itself. The noise is resonating from the right side of the fireplace. That said, the noise could be coming from the rear of the unit where the fresh air is piped down along the rear of the firebox; however, I cannot access that space without dismantling the entire fireplace - something Napoleon does not recommend.