CPSC White Paper Radiant Versus Catalytic Heaters

A fireplace. Yeah the type that you stuff logs into, produces 1000 times as much CO but the nutso overkill draft that sucks all of the heat and CO out of the room keeps people from dying.

It may be that more people have died because of combustion chamber cracks and holing than all of the unvented heaters put together. The moral of the story is using multiple CO detectors.