Share 'Gas Furnace in an Attic: To Replace or Not'

I have a client with an open combustion gas furnace in their attic. They recently had the attic spray foamed at the roof and end walls (enclosing the attic within the thermal boundary).  The house is an original two-story with basement (to be finished) and attic, and a crawl under a 2-story addition with a short attic. The house is located in northern VA (mixed climate). The house has two heatin…