Suburban Furnace exterior vent types (with pic)

Whatever you do I would definitely suggest a pair of these. I just finished having to remove and clean my Suburban furnace to clean out a dirt daubber nest bigger than my thumb. It blocked the sail switch, not allowing it to close. Not a 30 minute job to get to the inside of the fan chamber.

I agree that the lip is also essential to direct the heat away from your painted surface.