3
PREINSTALLATION REUIREMENTS
WARNING:
IF THE AREA IN WHICH THE HEATER MAY BE OPERATED IS SMALLER THAN
THAT DEFINED AS UNCONFINED SPACE OR IF THE BUILDING IS OF UNUSUALLY TIGHT
CONSTRUCTION, PROVIDE ADEQUATE COMBUSTION AND VENTILATION AIR BY ONE OF
THE METHODS DESCRIBED IN THE NATIONAL FUEL GAS CODE, ANSI Z223.1 SECTION 5.3
OR APPLICABLE LOCAL CODES.
This heater shall not be installed in a confined space or unusually tight construction unless provisions are
provided for adequate combustion and ventilation air.
The following formula can be used to determine the maximum BTU rating per the definition of unconfined space:
STEP ONE:
DETERMINE THE VOLUME OF SPACE IN CUBIC FEET.
LENGTH X WIDTH X HEIGHT = ________________ cu. Ft.
(Include adjoining rooms with doorless passageways or ventilation grills between rooms.)
Example: 24’ (L) X 16’ (W) X 8’ (H) = 3,072. cu. Ft.
STEP TWO:
MULTIPLY THE VOLUME OF SPACE BY 20 BTU/Hr. TO DETERMINE THE MAXIMUM BTU/Hr.
THE SPACE CAN SUPPORT.
Example:
3,072 cu. Ft. X 20 BTU/Hr. = 61,440 BTU/Hr.
(Maximum BTU/Hr. the room can support)
STEP THREE:
ADD THE BTU/Hr. OF ALL THE FUEL BURNING APPLIANCES IN THE SPACE.
VENT FREE HEATER_________________BTU/Hr.
GAS APPLIANCE #1 _________________BTU/Hr.
GAS APPLIANCE #2 _________________BTU/Hr.
Example:
VENT FREE HEATER 26,000 BTU/Hr.
GAS APPLIANCE #1
35,000 BTU/Hr.
TOTAL 61,000 BTU/Hr.
NOTE: DO NOT INCLUDE DIRECT-VENT GAS APPLIANCES. DIRECT VENT IS SEALED
COMBUSTION AND DRAWS COMBUSTION AIR FROM THE OUTDOORS.
THE SPACE IN THE ABOVE EXAMPLE IS AN UNCONFINED SPACE BECAUSE THE 61,000 BTU’S AN HOUR
USAGE IS LESS THATN THE 61,440 BTU’S AN HOUR AVAILABLE. IF THE TOTAL BTU’S AN HOUR USAGE IS
GREATER THAN 61,440
BTU’S AN HOUR THEN THE SPACE WOULD BE A CONFINED SPACE AND ADDITIONAL
AIR MUST BE PROVIDED.
The National Fuel Gas Code defines a confined space as a space whose volume is less than 50
cubic feet per 1,000 BTU per hour (4.8 m
3
per kw) of the aggregate input rating of all appliances
installed in that space and unconfined space as a space whose volume is not less than 50 cubic
feet per 1,000 BTU per hour (4.8 m
3
per kw) of the aggregate input rating of all appliances
installed in that space. Rooms communicating directly with the space in which the appliances are
installed, through openings not furnished with doors, are considered a part of the unconfined
space.
COMBUSTION AND VENTILATION AIR REQUIREMENT WORKSHEET
