Vent or 
Chimney
Each opening must be at least 100 sq. in. or 1 sq. in. per 1000 Btuh of total input rating, whichever is greater. See minimum area per table.
12" Max.
Each opening |
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to outside must |
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be at least |
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1 sq. in. per |
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4000 Btuh of |
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total input |
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rating. |
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- | 12" | |
Max | ||
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| Furnace |
Furnace
12" Max.
| Water Heater |
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Total Input | Free Area | Round Duct | |
Rating (Btuh) (Each Opening) | Diameter | ||
40,000 | 100 sq. in. | 12" | |
60,000 | 100 sq. in. | 12" | |
80,000 | 100 sq. in. | 12" | |
Figure 9. Equipment in a Confined Space with all Combustion Air drawn from Inside
Ventilation Louvers at each end of attic
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| 12" Max |
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| Minimum |
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| Total Input |
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| 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 10. Equipment in a Confined Space
with all Combustion Air drawn from
Outdoors through Exterior Wall
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
| Vent or |
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| Chimney |
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| Ventilation Louvers | ||
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| Outlet | NOTE: Air open- | |
| Air | ings shall each | |
| Water | have a free area | |
Furnace | of not less than | ||
Heater | one square inch | ||
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Alternate |
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Inlet Air | ing of all equipment | ||
Air Inlet | in the enclosure. | ||
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| Minimum |
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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 11. Equipment in a Confined Space
with all Combustion Air drawn from Outdoors through Vertical Ducts – from Ventilated Attic
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Ventilation Louvers For
Unheated Crawl Space
Figure 12. Equipment in a Confined Space
with all Combustion Air drawn from
Outdoors through Ventilated Crawl Space
and Ventilated Attic
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