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Clear Air Solutions

ENGINEERING HUB

Measure clearly.
Calculate consistently.

Practical SI tools for commissioning checks. Each result shows its assumptions and method so it can be checked against the approved design.

Manufacturer valve-flow calculator ↗HVAC field handbook ↗

CALCULATOR

Duct run pressure loss

Estimate losses along one constant-area section, then repeat for the other sections on the critical path.

Method and scope

Re = ρvD_h/μ; Δp_straight = f(L/D_h)ρv²/2; Δp_fittings = ΣK × ρv²/2; add known component losses at this flow.

Circular laminar flow uses 64/Re. Turbulent flow uses iterated Colebrook (Re ≥ 4000). Transitional flow and laminar rectangular flow are not estimated. Rectangular turbulent results use a hydraulic-diameter approximation; aspect ratio is limited to 10:1 and roughness/D_h to 0.05.

The pre-filled numbers are illustrative examples. Replace them with measured values or verified project inputs. Calculations do not save data or alter equipment.

Use the clear air path after any internal lining. Only dimensions for the selected shape are checked when you calculate.
Only used when rectangular is selected. Only dimensions for the selected shape are checked when you calculate.
Only used when rectangular is selected. Only dimensions for the selected shape are checked when you calculate.
One steady section flow.
Do not include fitting equivalent lengths if you enter their K values.
Illustrative value only. Check duct material, joints and condition.
Use density at the section’s temperature, pressure and humidity.
Illustrative room-temperature air value; update for actual conditions.
All coefficients must reference this section’s velocity. No generic fitting K is assumed.
Use manufacturer data for filters, coils, silencers and other components.
Reset example inputs

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