7
The Outlet air duct and Inlet air duct must have a free area of not less than 1 square
inch per 2000 BTUH based on the total input rating of all appliances in the space.
Chimney
Furnace Water
heater
Outlet air duct
Inlet air duct
A06465
Fig. 6 -- Combustion Air Taken From Outdoors Through Horizontal Ducts
The top opening and the bottom opening must each be 8-in x 18-in when a 105 size
furnace is installed. The top opening and the bottom opening must each be 10-in x 20-in
when a 120 size furnace is installed.
Chimney
Opening
Opening
Furnace Water
heater
A06466
Fig. 7 -- Free Area Openings
374RAN
