Find the mathematical inside diameter that carries a selected airflow at a selected velocity.
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Find the mathematical inside diameter that carries a selected airflow at a selected velocity.
Formula: Area = CFM ÷ velocity; diameter (in) = 12 × √(4 × area ÷ π).
Velocity-only preliminary sizing. Friction, fittings, flex compression, noise, available static pressure and Manual D may require a different size.
A whole-house square-foot estimate is a starting scenario. Climate, insulation, air leakage, windows, solar exposure, people and duct location can materially change the actual cooling requirement. A large unit can cool the air before removing enough moisture.
Manual J calculates sensible and latent loads. Manual S selects equipment using performance data. Manual D designs the duct system using room airflow, the blower’s pressure capability and the losses of ducts, fittings and components. Velocity-only duct dimensions do not complete that design.
One ton of cooling equals 12,000 BTU per hour. Thermal cooling kW describes heat removed; electrical input kW describes power consumed. Room/window AC estimates use the ENERGY STAR room table separately from the whole-house scenarios.
For heat pumps, cooling results alone cannot select the system: heating output at winter design temperature and backup heat need a separate evaluation. Material calculators estimate quantities; they do not size structural members or establish electrical or plumbing code compliance.