6
NOTE
: Both acoustical lining and fibrous ductwork shall comply
with NFPA 90B as tested by UL Standard 181 for Class 1 Rigid air
Ducts.
The Outlet air duct and Inlet air duct must have free area of not less than 1 square
inch per 4000 BTUH based on the total input rating of all appliances in the space.
The total free area or the ventilation louvers must have a free area of not less than 1
square inch per 5000 BTUH based on the total input rating of all appliances in the
space.
Chimney
Ventilation louvers
Outlet air
Inlet air duct
Furnace
(each end of attic)
[ends 1 ft (0.3m) above floor]
Water
heater
A06463
Fig. 4 -- Combustion Air Taken From Outdoors Through Vertical Ducts
(without louvers in foundation)
The Outlet air duct and Inlet air duct must have a free area of not less than 1 square
inch per 4000 BTUH based on the total input rating of all appliances in the space.
The total free area or the ventilation louvers must have a free area of not less than 1
square inch per 5000 BTUH based on the total input rating of all applinaces in the
space.
Chimney
Ventilation louvers
(each end of attic)
Outlet air
Furnace Water
heater
Inlet air
Ventilation louvers for
unheated crawlspace
A06464
Fig. 5 -- Combustion Air Taken From Outdoors Through Vertical Ducts
(with crawlspace louvers)
374RAN
