gas furnace in attic with blown in foam

Paul_69

some attics in mass. now have blown in foam insulation from soffits to ceiling. mass. save has been running rebates for customers to do this work. my question is if there is a gas furnace in attic is there now eneough air for combustion it there is ne vents open for air infiltration. is it ok if attic is big eneough in cubic feet for btu of furnace or does something else have to be done for combustion air.