Is there such a thing for this application. We'd like to do a NG fireplace with mantle on an inside wall. The only way we could exhaust would be either boxing something out the side, which would look very tacky, or going up, preferably inside the studs. Everything I see that goes "up" is very large. 10" diameter, would require this to either be visible or boxed in. I know Rinnai makes a zero clearance fireplace that would fit inside the walls of a 2x4, but they do not want you to go vertically, only horizontally, and max. exhaust length of 7'. What, if any, options does one have for this situation? P.S. Non vented not an option in my house!