I am thinking of encapsulating my crawl space in the Atlanta area to reduce moisture and mold issues. I currently have a 80% gas furnace in the crawl space as well as a gas tank water heater. I am wondering if there will be enough combustible air to run these appliances after the space is encapsulated. The basement waterproofing contractors I have talked with said the crawl space will not be airtight after encapsulating, but they will seal off the foundation vents. Do I need to put in a new 90% or greater direct vent furnace before encapsulating?