It is recommended to have a fresh air opening in a warmed space of a minimum of 2,800 sq/cm (3 sq./ft.) for every 10k BTU/Hr of heating output. For example, if you have Remington 140T-KFA-O in your workspace, you should have – • Two 32 inches broad windows open for 15 inches, or • A single-car garage door to be opened for 9 inches, or • A two-car garage door to be opened for 6 inches.