The Williams Forsaire furnace you inquired about can be mounted to the surface of a concrete block wall, but it will require a 9-1/4" hole drilled through the wall to the outside and if the wall is more than 8-1/2" thick, a vent extender may be required.� Williams also offers a top vent model that can be surface mounted using an optional kit. This option will vent through the roof rather than a side wall, so no penetrations would need to be made through your block wall.