AIR FOR COMBUSTION
AND VENTILATION
Continued
Unusually Tight Construction
The air that leaks around doors and windows 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 out- side atmosphere have a continuous water vapor retarder with a rating of one perm (6 x
b.weather stripping has been added on openable windows and doors and
c.caulking or sealants are applied to areas such as joints around window and door frames, between sole plates and floors, between
If your home meets all of these three cri- teria, you must provide additional fresh air. See Ventilation Air From Outdoors, page 7.
If your home does not meet all of the three criteria above, proceed to Determining
Confined and Unconfined Space
The National Fuel Gas Code, ANSI Z223.1/NFPA 54 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/Hr (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 installed*, 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 ventilation grills between them.
DETERMINING FRESH-AIR FLOW FOR HEATER LOCATION
Determining if You Have a Confined or Unconfined Space
Use this work sheet 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 pas- sageways 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 openings, add the volume of these rooms to the total volume of the space.
2.Multiply the space volume by 20 to determine the maximum Btu/Hr the space can support.
__________ (volume of space) x 20 = (Maxi- mum Btu/Hr the space can support)
Example: 2560 cu. ft. (volume of space) x 20 = 51,200 (maximum Btu/Hr the space can support)
3.Add the Btu/Hr of all fuel burning appliances in the space.
| ___________ Btu/Hr | |
Gas water heater* |
| ___________ Btu/Hr |
Gas furnace |
| ___________ Btu/Hr |
Vented gas heater |
| ___________ Btu/Hr |
Gas fireplace logs |
| ___________ Btu/Hr |
Gas water heater |
| __________ Btu/Hr |
Other gas appliances* + | __________ Btu/Hr | |
Total | = | __________ Btu/Hr |
*Do not include
Example: |
|
|
|
Gas water heater |
| 40,000 | Btu/Hr |
+ | 39,000 | Btu/Hr | |
Total | = | 79,000 | Btu/Hr |
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: 51,200 Btu/Hr (maximum the space can support)
79,000 Btu/Hr (actual amount of Btu/Hr used)
The space in the above example is a confined space because the actual Btu/Hr used is more than the maxi- mum Btu/Hr the space can support. You must provide additional fresh air. Your options are as follows:
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