I have an upflow natural gas 80% efficeient furnace. Does any one know where I can get an installation manual to see if can be installed horizontally? It is a

Comfortmaker
Made by International Comfort Products Corp
Model and Mfg. # GNEO75B12A1
Serial # L984255688
75,000 BTU input

As you may know it uses 3" metal flue and of course has no secondary heat exchanger and no drain for condensate.

Jimabc