CGN10A AND CGN6
NATURAL GAS HEATER
FRESH AIR FOR COMBUSTION AND VENTILATION
Continued
Unusually Tight Construction
The air that leaks around doors and win- dows may provide enough fresh air for combustion and ventilation. However, in buildings of unusually tight construction, you must provide additional fresh air.
Unusually tight construction is defined as construction where: a.walls and ceilings exposed to
the outside atmosphere have a continuous water vapor re- tarder with a rating of one perm
b.weather stripping has been added on openable windows and doors and
c.caulking or sealants are ap- plied to areas such as joints around window and door frames, between sole plates and floors, between
If your home meets all of the three criteria above, you must provide ad- ditional fresh air. See Ventilation Air From Outdoors, page 5.
If your home does not meet all of the three criteria above, proceed to De- termining
Confined and Unconfined Space
The National Fuel Gas Code (ANSIZ2123.1, 1992 Section 5.3) defines a confined space as a space whose volume is less than 50 cubic feet per 1,000 Btu per hour (4.8 m3 per kw) of the aggregate input rating of all appliances installed in that space and an unconfined space as a space whose volume is not less than 50 cubic feet per 1,000 Btu per hour (4.8 m3 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 in-
stalled*, through openings not furnished with doors, are considered a part of the unconfined space.
*Adjoining rooms are communicating only if there are doorless passageways or ventila- tion grills between them.
DETERMINING FRESH-AIR FLOW FOR HEATER LOCATION
Determining if You Have a Confined or Unconfined Space
Use this worksheet to determine if you have a confined or unconfined space.
Space: Includes the room in which you will install heater plus any adjoining rooms with doorless passageways or ventilation grills between the rooms.
1.Determine the volume of the space (length x width x height).
Length x Width x Height =
______ cu. ft. (volume of space)
Example: Space size
20 ft. (length) x 16 ft. (width) x 8 ft. (ceiling height) =
2560 cu. ft. (volume of space)
If additional ventilation to adjoining room is supplied with grills or open- ings, add the volume of these rooms to the total volume of the space.
2.Divide the space volume by 50 cubic feet to determine the maximum Btu/ Hr the space can support.
_____ (volume of space) ÷ 50 cu. ft. =
(Maximum Btu/Hr the space can sup- port)
Example: 2560 cu. ft. (volume of space) ÷ 50 cu. ft. = 51.2 or 51,200 (maximum Btu/Hr the space can sup- port)
3.Add the Btu/Hr of all fuel burning ap- pliances in the space.
Gas water heater* ________ Btu/Hr
Gas furnace ____________ Btu/Hr
Vented gas heater ________ Btu/Hr
Gas fireplace logs ________ Btu/Hr
Other gas
appliances* + ___________ Btu/Hr
Total = ________________ Btu/Hr
Example: Gas water heater
44,000 Btu/Hr
Total | = 50,000 Btu/Hr |
*Do not include
4.Compare the maximum Btu/Hr the space can support with the actual amount of Btu/Hr used.
__________ Btu/Hr (maximum the
space can support)
__________ Btu/Hr (actual amount of
Btu/Hr used)
Example: 46,100 Btu/Hr (maximum the space can support)
50,000 Btu/Hr (actual amount of Btu/Hr used)
The space in the above example is a con- fined space because the actual Btu/Hr used is more than the maximum Btu/Hr the space can support. You must provide additional fresh air. Your options are as follows:
A.Rework worksheet, adding the space of an adjoining room. If the extra space provides an unconfined space, remove door to adjoining room or add ventila- tion grills between rooms. See Ventila- tion Air From Inside Building, page 5.
B.Vent room directly to the outdoors. See Ventilation Air From Outdoors, page 5.
C.Install a lower Btu/Hr heater, if lower Btu/Hr size makes room unconfined.
If the actual Btu/Hr used is less than the maximum Btu/Hr the space can support, the space is an unconfined space. You will need no additional fresh air ventilation.
WARNING: If the area in which the heater may be operated is smaller than that defined as an unconfined space, provide ad- equate combustion and ventila- tion air by one of the methods described in the National Fuel Gas Code, ANSI Z223.1, 1992, Section 5.3 or applicable local codes.
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