Gas Water Heater Venting
This evening I noticed an odor typical of natural gas products of combustion coming up from the cellar.
It appears that our exhaust fans that draw in cool night air are also creating negative pressure, and that's affecting the gas water heater draft. Down cellar, I felt a LOT of spillage from the draft hood.
That inspired me to go look at the installation manual that I got with this WH, which (urk) I sort of didn't bother to read at the time (ack), and what I found concerns me even more.
I can probably deal with the draft problem for the summer just by keeping the a cellar window or two open.
But the manual says that the WH shouldn't share a flue with a power vented gas furnace. And that's exactly how it's set up - it shares an old masonry chimney (I think it's lined, but not sure) with a mid-90s vintage 80% efficiency power-vented furnace. That's the way the old WH was installed, and when I installed this one a few years back, I just popped the old flue pipe right on top of the new WH.
What do the experts here recommend? Is this a serious situation? What can happen when you connect a draft-vented WH to the same flue as a power vented furnace?
Do I need to consider a different WH? I'm really not interested in a tankless WH, but I might go for a power vented WH, if I can vent it through the sill with PVC. Especially if it's a two-pipe or coaxial direct vent (drawing combustion air from the outside).
If I do go that route, what kind of pitfalls am I in for with a direct vented WH? Any recommendations as to brand and model? Where would a DIYer find a PVWH or DVWH?