Black soot in Private Bathroom

[jeffprupis]

We have an '05 Monterey Ventura II. In our toilet room behind the toilet is a shallow cabinet. In the cabinet and to the left of the toilet (when when standing, the right when sitting) we find a black powdery soot. The toilet sits just aft of the refrigerator and above the aqua hot exhaust. Any ideas as to the source and a way to alleviate it and or clean it? TIA

[Joel Ashley]

I guess the first and second things that come to mind, Jeff, are the AC electrical panels that are in the upper cabinets there in my similar coach, and the obvious venue of the HydroHot exhaust.  Hopefully there wasn't a problem at one time in the 50 amp Main box that's on that (out)side. Any issue there I'd think obvious just from examining the box.

More thinkable but still barely imaginable is a rusted-out hydronics exhaust pipe.  The terminus is where moisture tends to collect/condense, and where corrosion attends.  Perhaps the scenario is a burner that is too rich and needs tweaking, with particulate emissions finding their way out via rust-outs just prior to the pipe's end, gradually making it up through a flaw in the coach undercarriage/floor and the wall unit, and condensing out in the cabinet wall.

That would be a pretty unbelievable tale, but anything's possible.  So I'd crawl under and check the HydroHot (probably not, as you wrote, an AquaHot on a Monterey) tailpipe, including feeling around the hard-to-see top for holes.  Have the coach blocked for safety before going under there of course, and the unit off and cooled down.  I'd think if it were much of a leak and coming in, that you'd smell diesel when the unit runs, especially in the toilet room.  Does the soot smell like diesel?  Is it greasy when you run a finger over it?  You did say it was powdery, so I assume not greasy.

One other notion is mildew that might resemble black soot.  I'm not sure how enough moisture could collect there, however, in order for mildew to grow.

Joel

[jeffprupis]

I guess the first and second things that come to mind, Jeff, are the AC electrical panels that are in the upper cabinets there in my similar coach, and the obvious venue of the HydroHot exhaust.  Hopefully there wasn't a problem at one time in the 50 amp Main box that's on that (out)side. Any issue there I'd think obvious just from examining the box.

More thinkable but still barely imaginable is a rusted-out hydronics exhaust pipe.  The terminus is where moisture tends to collect/condense, and where corrosion attends.  Perhaps the scenario is a burner that is too rich and needs tweaking, with particulate emissions finding their way out via rust-outs just prior to the pipe's end, gradually making it up through a flaw in the coach undercarriage/floor and the wall unit, and condensing out in the cabinet wall.

That would be a pretty unbelievable tale, but anything's possible.  So I'd crawl under and check the HydroHot (probably not, as you wrote, an AquaHot on a Monterey) tailpipe, including feeling around the hard-to-see top for holes.  Have the coach blocked for safety before going under there of course, and the unit off and cooled down.  I'd think if it were much of a leak and coming in, that you'd smell diesel when the unit runs, especially in the toilet room.  Does the soot smell like diesel?  Is it greasy when you run a finger over it?  You did say it was powdery, so I assume not greasy.

One other notion is mildew that might resemble black soot.  I'm not sure how enough moisture could collect there, however, in order for mildew to grow.

Joel

As always, you're full of thoughts and insight. It is in fact an Aqua Hot as we had it replaced under and extended warranty. I will crawl under and check, it is what I thought of first as I can't think of anything else that would create soot. Thanks Joel

[Keith Moffett]

The Hydrohot was a good call as that would have been expected as Joel points out.  Replacing it with an Aquahot was a great improvement no doubt.
The exhaust would be my first thought as well.  Did the exhaust get replaced with the Hydrohot?  We had a Hurricane that 3 previous owners couldnt work.  The problem wasa plugged exhaust.

If soot is getting in then so is exhaust gas and CO2.

Best of luck Jeff

[Jim Nichols]

Check the refrigerator flue or vent either from the roof looking down the roof vent, cover off,  or with flashlight from street side. If it can't be seen in either of those manners you may have to pull the refrigerator out part way to see. We put in an Amish cooling unit superior to the original. The Amish unit flue or vent is longer and closer to the roof. The vent is on the side where you have the soot. There were signs of some soot when I pulled the refrigerator out up in that corner and wall. Wash with soap and water or 409 spray to clean. You may have a poor flame from maybe a partially plugged burner because of rust and replacing the burner is in order.

[Joel Ashley]

That's a good call, Jim.  If the refer's chimney stack is out of line topside and the burner is running rich, misrouted soot could conceivably drift somewhere between to that adjacent cabinet surface.  But aside from repairing the alignment malady, I'd expect an adjustment to increase the percentage of air to the burner to resolve that without replacing it entirely. 

But a check that Jeff has a nice blue flame and cone would verify the soot-producing status or not.  If it's too yellow then there'd be incomplete combustion and too much soot, and your theory spot-on.  I'd also expect the fridge to have noticeably not been cooling all that well on gas.

Joel

[Bill Sprague]

We were getting traces of black soot in the bedroom and rear closet on our '04 Monterey that had a Cummins.  It turned out that there was an exhaust manifold leak. 

[george starkweather]

We had soot coming in around the bathroom vanity and the shirt closet in the bedroom on the driver side of our '05 Monterey. We discovered a board had rotted out above the forward part of the wheel well allowing diesel soot from the hydro hot exhaust pipe to get sucked into the coach. It was an easy fix.