Dulley, James. Furnace, Water Heater Need Combustion Air. Union News. December 19, 1989.

Abstract: This newspaper article discusses combustion air for furnaces. If a furnace is deprived of air it will not run efficiently and can produce carbon monoxide, which can be hazardous when inhaled. Common indicators that a furnace is not working properly include yellowish flames and flames that burn irregularly.

An effective way to supply air to a furnace is to build an enclosure with a duct to the outside around the furnace. A square inch of free space is required for every 4,000 Btu/hr. if the vent is vertical. The vent will need twice the space if it is horizontal. The outdoor duct should not run directly to the furnace opening because the draft will cause the furnace to malfunction. The furnace dealer can recommend specifications for the enclosure.