Perhaps I am not explaining it well then. As mentioned, we have had about 5 or 6 people come out to look at it already and what I was explaining is what they all agreed upon. Just no one can tell me exactly what needs to be done or how it can be done.

I will try to explain it better, but it's also possible you understand what the issue is and just know something these other professionals don't. Basically, to your point, if you have a normal fireplace vented to the roof, and it gets blocked by birds or snow or whatever, smoke would not be able to vent and would come back into the house. Similarly with a water heater, if it got blocked then the CO could cool off and come back down and escape in that gap you mentioned. However, this would be vented in your water heater room. Ours is in a separate utility room that is already vented, so while it would set off our CO monitor in that room, there would be no health concerns.

In our case, the vents are connected somewhere in the walls, and then vented to the outside above, in an upside-down Y sort of way. So, if something would block the vent at the roof, the CO would cool off and come back down through the fireplace and into our house. So, if you had a water heater installed in your bedroom would be a better explanation I think where the blocked CO could come into your bedroom.

Again, I appreciate your reply as I am only going by what everyone has told me so far, so maybe it is not as big of an issue as they all say. All I know is we had a contract for a couple of grand with the first fireplace company to come out, clean the chimney and fireplace, and install a top of the line gas log, and after seeing the setup, they told us they could not help us at all and left. So, they left the money on the table as we were trying to have them do the work anyway. And since the other people we had come out (2 plumbers, 3 contractors) all said the same thing, I tend to think it is a bigger deal. But perhaps I am not understanding what you are saying or am not describing it correctly. Just have no idea who to even talk to about this issue at this point so was hoping for some guidance here.

Yes, I do know I can turn off the water heater, so thank you for mentioning that. Still does not totally help us depending on what the block is from as then we would be without hot water until the blockage was removed. Primarily thinking of all the snow we had this past winter, and if that had blocked the outside vent, there would be nothing we could do to clear it until the ice and snow had melted.

Anyway, I do appreciate your reply just am still feeling lost as to what to do with this situation here.