WTF?

[Steven Hockstein]

I was not sure if I should post this in the HVAC or plumbing section.

 

The good news is that they did not have to make an extra hole in the roof for the exhaust fan termination.

[Marc]

I know it's wrong. The guy who did it knew it was wrong, but what's the worse that gonna happen?  Gas traps will keep it it from coming out of basin, toilet and tub drains.

[Bill Kibbel]

If the B-vent was closer than the vent stack...

[inspector57]

The worst is the sewer gas that migrates out the fan when it is off. There is a reason we have traps  between the vent/soil stack and the interior of the house. Of course I guess and explosion from concentrated methane might be worse.

[rjbrown2]

Methane is not going to be the issue from an explosion in this set up. Methane (Natural Gas) is CH4 whose molecular weight is 16. Air has a molecular weight just over 28 (since it is mostly N2) The Methane is so much less dense than air it it will proceed straight out the vent.

The culprit in any explosion in this rig would be Hydrogen Sulfide (H2S) whose molecular weight is 34. This gas is more dense than air and if it makes it up the vent to the fan 'junction' it could back spill into the bathroom.

That being said, the explosion concentrations in air for H2S are from about 4.5 to 45%. This is so much higher than the allowable limits that if you started getting any serious H2S concentrations in the area, it would run you out from the irritation of your eyes, mucous membranes and lungs before there would be any explosion.

Still wrong though.

<bb

Edited February 8, 2018 by rjbrown2
typo

[Erby]

I don't see it as an explosion risk, just sewer gas stinking up the bathroom.  May depend on which way the wind is blowing.