Our garage was converted into a family room. The furnace is in it and has had a closet built around it. We would like to cut down the noise level and were looking to insulate the walls but the doors are accordion slatted door. I was told that slatted doors were used to vent off heat. Could we put in insulated solid doors and vent into the crawl space under the house. The furnace is against an inside wall. If this is possible, how large of a vent will be needed?
You need to have adequate clearance to combustible wood etc from the furnace as well as air for combustion and ventilation of the furnace and safety, insurance reasons , codes etc. I would leave it alone or get a Pro to assess it and look up the specs in the code book.