Why "if running an unvented flame"?
There are no free rides, and with only a few exceptions (like maybe nitro-methane, burning magnesium under water, and explosives) all that burns on our planet consumes atmospheric oxygen. Methane, ethane, propane, butane, kerosene, alcohols, gasoline, wood, coal, etc are all carbon based. If the combustion residues/gases can escape our enclosed space via a chimney or vent of some sort, the bad stuff leaves ones enclosure and atmospheric air of the typical composition seeps in via unsealed avenues with life being good. If there is no avenue of escape, those toxins accumulate in our room until ones flame is literally starved to death. When O2 begins to get short, combustion keeps going, but it will generate CO as opposed to the normal CO2. Life ends.
Put a lighted candle in a jar and screw on the lid. Ones flame does not last long.
That's why with even a wood stove we have a chimney and an intake to bring in outside air.
I'm old and recall a time when power was out for days due to a heavy snow event. The old man brought a burning charcoal grill inside as a heat source. I also remember getting weary and suffering a severe headache. Headaches are an extremely rare event for me. We're lucky the whole family lived through that night.
