What is this "vent" for?

I've had an intermittent problem for some time - after emptying tanks I sometimes get a strong sewer smell in the vicinity of the bathroom, but I've never really been sure it was actually from the bathroom. In that immediate area is the sink in the bedroom, the shower and across the hall, the bathroom with sink and toilet. I could never really tell exactly where the smell was the strongest.

Yesterday I dumped the gray water and inadvertently left the valve open (I am hooked up but am aware that sewer gases can come back into the rig so generally I don't leave the valve open). Could smell some fumes last night and even stronger this morning, again not realizing I'd left the valve open. I spent some time trying to localize the smell and came across this vent (see attached). I'd never really given it much thought, but as I kneeled down and had a sniff I could smell some of the fumes.

As I stood and pondered this vent, I began wondering what it was for. Clearly not for the furnace, as that is floor-ducted through metal registers. Obviously not the overhead ducted AC. So I removed it, and it's not a supply or return register at all, and seems to be nothing but a small access to the plumbing beneath the shower pan; I have no idea why Newmar would install a vent there rather than a solid access cover.

So to my question, why is is setup this way? And having looked around in there with a flashlight and with things seemingly OK, why am I getting a sewer gas smell there? (Clearly the smell is coming back up through the gray water system, but that should all be plumbed tight and it doesn't seem like there should ever be any smell under the shower pan area, even if gasses were being passed up through the hose.)

Scott, IIRC our Monaco has the same vent in the same place. I probably figured it was either a "vent" to help circulate air beneath the shower or, as you suggest, an access port. Never had any smell emanating from there.

We have a similar vent under our shower that is part of the furnace ducts.  It blows hot air when the furnace is operating.

Is there an air admittance device under the shower?

BigLarry said:

We have a similar vent under our shower that is part of the furnace ducts.  It blows hot air when the furnace is operating.

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I've had the vent off, it's not attached to the furnace ducting

kdbgoat said:

Is there an air admittance device under the shower?

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Good thought, I pulled the vent off again and not as far as I can tell. It appears that the plumbing tees into a proper vent which disappears up behind the shower stall.

Sun2Retire said:

Good thought, I pulled the vent off again and not as far as I can tell. It appears that the plumbing tees into a proper vent which disappears up behind the shower stall.

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This might be the key " which disappears up behind the shower stall" Can you find where it vents to the outside? Or is it just stubed up behind the showerstall? Maybe it came apart or is pluged leting the vent gases back into the space under the shower.
Bill

As near as I can figure, it is the return air vent for the furnace from the bays.  When the furnace is on there is a vent to the bay to heat the water area and this is the return to the living area so the air gets back to the furnace inlet.  If you are getting odor from it, you have a leak, if not water at least air, from the black or grey systems in the bay area.

I have a similar vent in my 2001 Dutch Star and that is what I have concluded.

Jim Godward said:

As near as I can figure, it is the return air vent for the furnace from the bays.  When the furnace is on there is a vent to the bay to heat the water area and this is the return to the living area so the air gets back to the furnace inlet.  If you are getting odor from it, you have a leak, if not water at least air, from the black or grey systems in the bay area.

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Ahhhh.... that makes sense, and with temps in the 20s I have been running the basement blower (but when I've had the smell before I have not been running the blower).

For another issue I think I may to have to remove the water bay "control panel" (or whatever it's called) so I can replaced a valve behind the panel. At that point I might be able to see a little better back in the black and gray tank areas and see if I can find something obvious.

WILDEBILL308 said:

This might be the key " which disappears up behind the shower stall" Can you find where it vents to the outside? Or is it just stubed up behind the showerstall? Maybe it came apart or is pluged leting the vent gases back into the space under the shower.

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I looked on the roof and I do have a proper vent in the exact shower location where the pipe disappears behind the enclosure, so it's not just an air admittance valve. There is no way to get to that pipe without tearing the whole shower out.

Possibly it's a return air vent for the furnace.  Does the bathroom door fit fairly snug to the floor?  If so, you need another way for the hot air blowing out of the floor vents to leave the room.

The return path may be through cabinets, plumbing runs, etc. and not a physical duct.

The roof vent may just be for the shower drainpipe or one of the holding tanks, with no connection to mystery vent or any other part of the RV interior.

For what it's worth, I have the same vent in the same location in my Ventana. It blows hot air when the furnace is on.