Question about combustible walls?

I believe plaster and paint are combustible, no? Also I assume you mean you'd run a separate liner and not use the same flue at the water heater?

Paint & plaster don't matter. What could be the closest possible combustible material in a straight horizontal superman x-ray vision look from where the side of the stove is to out through the chimney? If that distance is in excess of the candidate stove's minimum Clearance To Combustibles to the side, you're good.

In a word, no. Gypsum plaster becomes like rock, and it is not combustable. Gypsum plaster is considered a 2 hour firewall over most materials, and over fireplace brick it is basically about as fireproof as you are going to get. Paint does not matter, though it is likely going to discolor over time near a heat source. I think you can get color tinted plasters and that will hold up better than paint will over time. Or you can tile over it. Actually tile over the fireplace may be a better option for durability over time, and it looks good.