Shared flue and Carbon Monoxide concerns

[dt45]

I think you would be making the whole system safer with outside air on the bottom stove, (@bholler ?) especially if the house is getting depressurized due to the recent weather sealing. The downstairs stove won't contribute to the depressurization, which makes the upstairs stove safer when draft is weak.

Can someone confirm/deny that outside air supply on the downstairs stove would make such setup safer? I've searched through older threads and internet and I can't find anything about using outside air supply on shared flues.

 

[jetsam]

Can someone confirm/deny that outside air supply on the downstairs stove would make such setup safer? I've searched through older threads and internet and I can't find anything about using outside air supply on shared flues.

I'm guessing, but it makes sense to me, especially after you said they had been tightening up the house.

I am not going to venture an opinion about outside air on the upstairs stove... it would obviously be a draft reversal hazard, but then the whole stove is already such a hazard because it's on the same flue as the downstairs stove, so it's already possible for the downstairs stove to vent through the upstairs stove.

Honestly though, it's not your house and you can't do a new roof penetration, which is what's needed. But you can open a window a little bit to offset the house tightening and keep a CO alarm by both stoves, and it should be safer than it's ever been.

 

[dt45]

Thank you for your answers jetsam, they are also very useful. Your guess makes sense, I was just wondering if there may also be some other dynamics at play (I've read some bad things about outside air supply in some conditions, even on single flue).

I'm asking that question, because I'm looking for a new downstairs stove (I'm hoping it would help with those overnight CO ppm readings). Cheaper stoves don't have option for outside air supply, so I have to decide whether this increased cost&complexity is worth the trouble and won't (in some conditions) make this setup even less safe.