My fire didn’t work hard today either. I only put 12 lbs on this morning (about half a bucket of nut). Then 8 lbs on around 4pm. I’ll put a full bucket on tonight, maybe 20-22 lbs. My house was 73 most of the day, 71 now.
That sounds like you are running a good efficient fire. I bet your draft fully closed is running right where it needs to be. As your fire gets hotter, your draft pulls more.
I am at the exact same stage you are. I need to run cold air into my burner, and my gas water heater is just T’ed into my masonry chimney along with the coal burner. My setup wouldn’t take the cold air quite like yours would, but anything would help.
I honestly think my chimney is perfect for me. I was running around 300-350 degree stack temp and had my damper shut all the way. I caped the natural gas pipe for a few minutes to see what happened and my draft was too much. It shot up from -0.05 to -0.07. The damper was closed as much as it closes. Once you get a meter you could see exactly what it does for you. My chimney has got to be over 20 feet too, half exposed & half inside. I don’t think I’m going to leave it the way it is. When I upgrade to a stoker with a barometric damper I could see venting the gas water heater different. The 3 inch natural gas vent pipe acts as a barometric damper, sucking in room air, always opened 3 inches.
The natural gas or propane vapors mixing with coal shouldn’t be a problem. I heard mixing anything oil fired with wood smoke would be a big
nfire: problem. I’m not sure what type of water heater you have(It might be propane from your pics). Its just something to think about.