MODU-FIRE® Forced Draft Gas-Fired Boiler
15
Table of US Minimum area of ventilation openings per boiler (sq inches)
MFD
MODEL
AIR SOURCE
INDOOR AIR SUPPLY
OUTDOOR AIR SUPPLY
SAME FLOOR
DIFF FLOORS
ONE OPENING
TWO OPENINGS
DIRECT
VERT
DUCT
HORIZ
DUCT
N750
750
1500
250
188
188
375
N1000
1000
2000
333
250
250
500
N1500
1500
3000
500
375
375
750
N2000
2000
4000
667
500
500
1000
3.5.2.2 Air Inlet Requirements – Canada (CAN/CSA B149.1)
A. Ventilation of the space occupied by fuel burning appliance(s) or equipment shall be supplied by a ventilation
opening at the highest practicable point communicating with the outdoors. The total cross sectional area of
the ventilation opening must be either 10% of the net free area required for combustion air or 10 sq. in. (6500
mm
2
), whichever is greater.
B. Use the following opening calculation for MACH
®
or MODU-FIRE
®
FD boilers: When combustion air is sup-
plied for a forced draft burner by natural airflow from the outdoors and there is no draft regulator or draft hood
in the same space, there shall be a permanent opening with a cross sectional area not less than 1 sq. in/
30,000 Btu/Hr (70 mm
2
/kW) of the total rated input to the burner(s). This opening must not interfere with the
ventilation air opening defined in paragraph A.
C. Use the following opening calculation for P-K THERMIFIC
®
boilers or other natural draft or fan-assist ap-
pliances: When combustion air is supplied for natural or fan-assisted burners by natural airflow from the out-
doors, there shall be a permanent opening with a cross sectional area not less than 1 sq. in/ 7000 Btu/Hr (321
mm
2
/kW) up to and including 1,000,000 Btu/Hr plus 1 sq. in. / 14,000 Btu/Hr (155 mm
2
/kW) in excess
1,000,000 Btu/Hr. This opening must be either located at or ducted to a point not more than 18 in. (450 mm)
nor less than 6 in. (150 mm) above floor level. This opening is in addition to the ventilation air opening de-
fined in paragraph A.
D. When combustion air is supplied by natural airflow into a space containing both types of appliances described
in paragraphs B and C, the cross sectional area of the opening shall be not less than the sum of the cross
sectional areas for all appliances in the space as calculated by the applicable method . This opening is in ad-
dition to the ventilation air opening defined in paragraph A.
E. When a duct is used to meet the requirement for combustion air supply, as described in paragraphs A through
D, above, the opening of the duct shall be located so there is no possibility of cold air affecting steam or water
piping, electrical equipment or mechanical equipment.
F. When combustion air is supplied by mechanical means, an airflow-sensing device must be installed. It must
be wired into the pre-ignition limit string to prevent the burner from starting or to stop an operating burner in
case of air supply failure.
G. When all combustion air is supplied through a make-up air heater, and the appliance is interlocked to the hea-
ter, the requirements of paragraphs A through F do not apply.
NOTICE!
1. The free area of a combustion air supply opening is calculated by deducting the blockage area of
any fixed louvers, grilles or screens from the total area of the opening.
2. Screens shall be not smaller than ¼”
3. Motorized louvers shall be interlocked with the appliance so that they are proven open prior to
main burner ignition and operation
