PRE-INSTALLATION REQUIREMENTS
Combustion and Ventilation Air Requirement Worksheet (Vent Free only)
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.
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