Good Morning. A Home Inspector just finished an inspection on a home I just completed and told the homeowner that all 92% Eff. Furnaces need outside Combustion air. The Carrier website says that the unit is actually a “Sealed Combustion Unit”, but doesn’t say wheter or not we need to pipe air into it. The unit is located in a good sized crawlspace. My HVAC sub is very competent and I believe that they installed the unit correctly (without an outside vent for it), but just wanted to get another opinion to offset the Inspector’s.
At what point do we need an outside vent for combustion air? Does it normally connect directly to the unit or can we use the air in the crawlspace? The crawlspace is 200SF with 3-4′ headroom.