Preferred 4” Hoods
When you have a 4” (10cm) Hood
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| Maximum length of 4” diameter metal duct. | ||||
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Number of 90˚ |
| Rigid | Thick Wall Flexible Metal | |||
elbows/bends |
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| (fully extended) | |||
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0 | 64ft |
| 19.5m | 36ft |
| 10.9m |
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1 | 54ft |
| 16.5m | 31ft |
| 9.4m |
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2 | 44ft |
| 13.4m | 27ft |
| 8.2m |
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3 | 35ft |
| 10.6m | 25ft |
| 7.6m |
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4 | 27ft |
| 8.2m | 23ft |
| 7.0m |
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Acceptable 2 1⁄2”Hood
When you have a 2 1⁄2” (6cm) Hood
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| Maximum length of 4” diameter metal duct. |
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Number of 90˚ |
| Rigid | Thick Wall Flexible Metal | |||
elbows/bends |
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| (fully extended) |
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0 | 58ft |
| 17.6m | 28ft |
| 8.5m |
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1 | 48ft |
| 14.6m | 23ft |
| 7.0m |
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2 | 38ft |
| 11.5m | 19ft |
| 5.7m |
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3 | 29ft |
| 8.8m | 17ft |
| 5.1m |
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4 | 21ft |
| 6.4m | 15ft |
| 4.5m |
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For exhaust systems not covered by the exhaust duct length charts (such as multiple unit
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