Vent or
Chimney
Each opening to outside must be at least 1 sq. in. per 4000 Btuh of total input rating.
- | 12" |
|
Max |
| |
|
| |
|
| Furnace |
- |
|
|
12" Max | Water Heater | |
| Minimum |
|
Total Input | Free Area | Round Duct |
Rating (Btuh) | (Each Opening) | Diameter |
40,000 | 10 sq. in. | 4" |
60,000 | 15 sq. in. | 5" |
80,000 | 20 sq. in. | 5" |
100,000 | 25 sq. in. | 6" |
120,000 | 30 sq. in. | 6" |
140,000 | 35 sq. in. | 7" |
160,000 | 40 sq. in. | 8" |
Figure 12. Equipment in a Confined Space with all Combustion Air drawn from Out- doors through Exterior Wall
Ventilation Louvers at each end of attic
| Vent or |
| |
| Chimney |
| |
| Ventilation Louvers | ||
| (each end of attic) | ||
| - |
| |
| Outlet | NOTE: Air open- | |
| Air | ings shall each | |
| Water | have a free area | |
Furnace | of not less than | ||
Heater | one square inch | ||
| |||
|
| per 4,000 Btuh of | |
Alternate |
| the total input rat- | |
Inlet Air | ing of all equipment | ||
Air Inlet | in the enclosure. | ||
| - |
| |
| - | - | |
Ventilation Louvers For
Unheated Crawl Space
Figure 14. Equipment in a Confined Space with all Combustion Air drawn from Out- doors through Ventilated Crawl Space and Ventilated Attic
Vent or |
Chimney |
Vent or
Chimney
Attic
Insulation 
Furnace
Water Heater
Air Duct must be at least 1 sq. in. per 4,000 Btuh of total input rating.
Ducts must extend above attic insulation.
Air Duct must be at least 1 sq. in. per 4,000 Btuh of total input rating.
12" Max
Air Duct | Air Duct | |
must be | ||
Furnace | at least | |
1 sq. in. | ||
| per 2000 | |
| Btuh of | |
Air Duct | total input | |
rating. | ||
| ||
Water Heater |
|
| Minimum |
|
Total Input | Free Area | Round Duct |
Rating (Btuh) | (Each Opening) | Diameter |
40,000 | 10 sq. in. | 4" |
60,000 | 15 sq. in. | 5" |
80,000 | 20 sq. in. | 5" |
100,000 | 25 sq. in. | 6" |
120,000 | 30 sq. in. | 6" |
140,000 | 35 sq. in. | 7" |
160,000 | 40 sq. in. | 8" |
| Minimum |
|
Total Input | Free Area | Round Duct |
Rating (Btuh) | (Each Opening) | Diameter |
40,000 | 20 sq. in. | 5" |
60,000 | 30 sq. in. | 6" |
80,000 | 40 sq. in. | 7" |
100,000 | 50 sq. in. | 8" |
120,000 | 60 sq. in. | 9" |
140,000 | 70 sq. in. | 10" |
160,000 | 80 sq. in. | 10" |
Figure 13. Equipment in a Confined | Figure 15. Equipment in a Confined Space |
Space with all Combustion Air drawn from | with all Combustion Air Drawn from the |
Outdoors through Vertical Ducts – from | Outside through Horizontal Ducts |
Ventilated Attic |
|
15
