Why is my loss so high?

Usually undersized duct (high velocity). Doubling velocity roughly quadruples friction and fitting losses. Step up a size to cut fan power.

Does this cover the heat exchanger?

No — a plate or wheel adds its own pressure drop (typically 80–250 Pa). Add that to the total here when sizing the supply/extract fan.

ZIBO QIYU · Heat Recovery Tools

Duct Pressure Loss Calculator

Estimate fan static pressure needed for a run of sheet-metal duct — friction loss plus elbows, entry and exit. Round or rectangular.

Duct shape

Airflow

m³/h

Diameter (round)

mm (or side A for rectangular)

Side B (rect only)

mm — leave blank for round

Duct length

90° elbows

count (ζ≈0.3 each)

Velocity

—

Friction loss

—

Fitting loss

—

Total static pressure

—

Component	Loss (Pa)	Share
Friction (length)	—	—
Elbows	—	—
Entry + exit	—	—

Assumptions: air density 1.2 kg/m³; friction factor λ=0.02 (typical galvanised sheet); entry ζ=0.5, exit ζ=1.0, elbow ζ=0.3. Add ~10–20% margin and filter/AHU losses for fan sizing.

How it is estimated

Velocity pressure p_v = 0.6·v² (Pa). Friction = λ·(ρ·v²/2)/D·L. Each fitting adds ζ·p_v. Total static pressure is the sum — that is the minimum your fan must deliver at the design flow.

Frequently asked questions

Why is my loss so high?: Usually undersized duct (high velocity). Doubling velocity roughly quadruples friction and fitting losses. Step up a size to cut fan power.
Does this cover the heat exchanger?: No — a plate or wheel adds its own pressure drop (typically 80–250 Pa). Add that to the total here when sizing the supply/extract fan.
Round or rectangular?: At equal area, round has less surface and lower friction; rectangular is used for space constraints. This tool converts rectangular to an equivalent hydraulic diameter.

First-order estimate for preliminary duct sizing. Zibo Qiyu sizes full AHU and heat-recovery systems with pressure budgets — request a quote.