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    HVAC Duct Sizing Calculator — Free Friction Rate Tool

    Should I use flex duct or sheet metal?

    Sheet metal has lower friction loss and longer life, so it is preferred for trunk lines. Flex duct is acceptable for short branch runs (under 10 ft) where it is fully stretched and properly supported — sagging flex duct can lose 50% of its rated capacity.

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    Use the HVAC Duct Sizing Calculator — Free Friction Rate Tool to get an exact answer for your inputs.

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    Related questions

    Estimates and general guidance only. Verify against your local code and AHJ before any installation. Gas, electrical, and refrigerant work is hazardous to untrained users.

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