My question is where the furnace at water heater connect before they enter the chimney. Is there potential for the larger furnace flue to back draft thru the water heater flue?
Furnace was installed 15 years ago. I would imagine this is when the liner was installed.
Probably not the best idea to paint the flue piping.
The first picture is a problem, the hot water tank should vent above the furnace. Yes there is the potential for back drafting.]
Picture 2, if I am looking at it from the top of the chimney down, the vent connector extends too far into the chimney, and looks like its pointed down. Either way proper venting may be prevented.