# Proper intake duct size for 80,000 BTU gas furnace?



## Bitters (May 28, 2014)

Depend's on the CFM.


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## ben's plumbing (Oct 6, 2011)

Rectangular duct...8x14 = 490 cfm..8x16=580 cfm.

round metal pipe..14" 750 design airflow
'"""""""""""""""""""""" 16" 1200 design air flow


flexible duct14"= 700 cfm
"""""""""""""""16"= 1000 cfm design airflow


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## beenthere (Oct 11, 2008)

16" is border line small for a 80,000 BTU input 95% gas furnace. But a whole heck of a lot better then a 14" that would be barely good enough for a 60,000 BTU furnace.


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## oldbikes (Sep 5, 2014)

A 10 x 20 would be about the right size, If the ca return is undersized how about the Warm Air vents?


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## mikelee221 (Dec 16, 2014)

Thanks everyone. I convinced the original installer to change it to 16". From the way it sounds.... 20" is even better... 

Hopefully this will fix the issue.


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## hvac benny (Dec 29, 2009)

mikelee221 said:


> Thanks everyone. I convinced the original installer to change it to 16". From the way it sounds.... 20" is even better... Hopefully this will fix the issue.


I'm assuming it didn't take too much convincing, since he suggested it.


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