Hello all, Had a little scare the other day when two of our three carbon monoxide testers went off. Fire department and gas company confirmed the presence. The last 5 days has been spent diagnosing the cause. Furnace? Fireplace (FPX36)? The combination? Had the heat exchanger examined, no issues of concern. Thought the FPX36, once the fan is blowing in, could cause the furnace to have an issue (ran both of them on some cold morning to keep the house at the same temp while the fireplace got going). Not so. So I've come to the fireplace. Little background....I'm the poster a couple month ago that was having issues with smoky starts because of air coming down the chimney. I solved that by burning a medium size piece of paper up on the shelf just under the chimney hole. I pose these question... 1) On colder mornings, could the draft be reversing early in the morning once the fire has cooled down enough? 2) If so, does pushing the air control all the way to the right COMPLETELY shut air off or does it leave it slightly open. 3) If it leaves it slightly open, then what do I do? Thanks for any help as I love the fireplace but if I can't solve this issue (I haven't confirmed this is the issue yet) then I need to fix it.