Vibrations from wall-hung combi are driving me crazy

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Old 10-27-13, 08:17 PM
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Vibrations from wall-hung combi are driving me crazy

Hi all,

I've just installed a Navien CH-240. Unit is heating the house nicely (other than some short-cycling...working on that in a separate thread) but when the exhaust fan is running at all (even the lowest speed), I feel and hear the vibrations in the room above, which happens to be the master bedroom. Not the best conditions for sleeping...

I noticed this directly after the install, and spoke to the local Navien rep to get some ideas. He told me that he uses rubber washers to isolate the unit from the wall. So, I remove the unit (gotta love those unions), put 3 1/8" rubber washers (from local hardware store) between the wall mount and the unit. Also adjusted the the vent pipes (3" PVC) so they are not directly touching the floor joists.

After those changes, the vibration sound is better, but it still sounds like a semi truck is idling in the distance. I can hear it over the sound of my sound machine at night. This sound is only really an issue in the master bedroom...not in the boiler room.

I called Navien directly and their tech support had us remove the fan and start the boiler, so we could confirm that the vibration is coming from that (and not anything to do with combustion). I had my wife hold the fan in her hand during startup, and the sound was 100% gone in the master bedroom.

So the issue COULD be the fan, but the fact that I can hear the vibration even when then fan is on it's lowest speed (and not vibrating that much) makes me think it might have to do better at isolating the boiler from the house.

Some questions:
  • Should it be necessary to use rubber mounts around all the pipes leading to (and leaving) the boiler? Feels a bit excessive. I have a hard time believing this is the norm for wall-hung mod/cons or tankless water heaters.
  • Should I make sure the vent has no contact at all with the house? Right now it's just contacting the house at the point where it goes through the house (to vent outside)
  • Should I build a platform for the boiler to sit on (instead of hanging it on the wall)?

Appreciate any help you can give!
 
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Old 10-29-13, 06:29 PM
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Good news!

Navien sent me a new exhaust fan, I plugged it in, and 90% of the vibration problems went away. It went from a semi truck idling outside to more of a refrigerator running in the distance. I can still hear a small rumble during the post purge but nothing that should keep me up at night. Seems to be more of an issue when the fan spins at certain speed...not all the time.

Seems like there are some quality control issues on their exhaust fans (didn't take much prodding to get their tech support to send me a new one), but at least they sent me one free and quick.

Hopefully this is helpful to someone else.
 
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Old 10-29-13, 06:37 PM
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A boiler mounted to a frame wall could, I think, be particularly susceptible to noise transmission. Mounted on a concrete basement wall, not so much. Was yours on a frame wall?
 
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Old 10-29-13, 06:52 PM
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Interesting... I wonder if the replacement blowers are being balanced to a tighter tolerance?
 
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Old 11-12-13, 02:15 PM
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Thanks for the replies, gilmorrie and NJ Trooper.

gilmorrie, it's mounted to 3/4 plywood, and the plywood is fastened to concrete block wall. About 3/8" of rubber washer between boiler and plywood.

NJ Trooper, I have the same thought about the replacement motor. Does seem to be manufactured to tighter tolerances.

I have a follow-up to my follow-up: even though the exhaust fan vibration was significantly reduced after I installed the replacement fan, it seemed to get louder after a few weeks. To make sure the issue was fan-related, I temporarily put a fernco fitting between the fan and the boiler, and it seems to be doing a great job of isolating the fan vibration.

However, on some cold nights, when the system is in space-heating mode, I can hear a distinct low-frequency rumble in my bedroom above the boiler. Seems pretty noticeable at a certain modulation rate. We had a cold night last night and the boiler was at that modulation rate for several hours, so I had a bit of rough nights sleep.

From some of the web research I've done, it looks like sometimes a vibration on these units is related to issues with combustion. Either low/high gas pressure or air/fuel mix. I'm considering either attempting that myself (I can borrow a combustion analyzer and manometer) or hiring a pro to do it. I'm just hesitant to spend time and money on that issue if it's a red herring.

My old atmospheric boiler was so quiet...sometimes I miss the beast Just not the utility bills that came with it.

If I can't get the Navien to behave I might have to replace it next summer with something known for quiet running. I'm hoping it is possible to have a mod/con boiler installed in a utility room below a bedroom without running into such noise issues. I expected a bit of fan noise but this low-frequency thing is going to send me to the mad house...

Questions:
  • Have you heard of such vibrations being related to gas pressure/combustion issues?
  • What methods do you recommend to damping vibrations from the boiler? I'm using rubber washers between boiler and wall, and considering fernco (or high-temp alternative) coupling in middle of PVC vent. I figure if I can't stop the vibration I SHOULD be able to keep it in boiler room.
  • If I can't silence the Navien setup, what are some good, quiet boiler options? A contractor recommended a Lochinvar Knight...thoughts?

Thanks for your help!
 
 

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