Construction Engineering Verified Calculator

Fan Total Static Pressure Calculator

Total fan static pressure from a schedule of duct, fitting and terminal losses, with the margin against the static available and the item carrying most of the loss.

Fan Static Pressure Engine • Loss Schedule Driven

System & Loss Schedule

Loss item (one segment each)
Within available static
Exceeds available static

The duct run split into one segment per loss item, each labelled with the engine's own share of the total, and the summed static shown against the static available. Schematic only — not to scale and not a construction drawing. Segment width is the item's SHARE of the summed loss, not its length in metres. Every loss is entered by you; this tool holds no duct-friction or fitting database. The available static is a target you supplied, not a rating the tool knows to be safe.

Available static pressure (P_avail)

A target you supply, not a rating this tool knows to be safe.

Loss items

Item	Δp (Pa)	K	p_v (Pa)

Result

Total static loss — Pa

Every entry from your schedule, summed.

Margin against available — Pa

Available static less the summed loss.

Largest single loss —

The item carrying most of the pressure — the first thing to re-check.

Build-up

Direct drops: — Pa
Coefficient / velocity-pressure: — Pa
Unresolved items: —

Assumptions & limitations

Every loss is entered by you. This tool holds no duct-friction table, roughness data, fitting database or air-property table, and looks nothing up.
A coefficient without its velocity pressure cannot be turned into a pressure drop, so that item is reported as unresolved rather than given an arbitrary velocity.
Steady-state pressure loss only. Acoustic attenuation, fan noise, duct leakage, system-effect factors, measurement allowance and start-up motor over-sizing are not covered.
The available static is a target you supplied. It is not a rating the tool knows to be safe for any particular system.

Workspace

Continue where you left off

Saved calculations in this browser can be reopened with their inputs intact.

Open Workspace

What this calculator does

Sizing a fan from a list of duct resistances is where pressure is lost most often: the straight ductwork is added up carefully and the fittings, terminals and plant items are then forgotten. This tool totals them explicitly and reports what is left of the static you had available.

How to use it

Add one row for every loss in the run — straight duct, fittings, terminals, coils, filters, dampers.
Enter a direct pressure drop where you have one, or a loss coefficient together with the velocity pressure it acts on.
A coefficient with no velocity pressure is reported as unresolved rather than given an invented velocity.
The result reports the margin against the static you have available, and names the item carrying most of the loss.

Governing method

Governing Formula

TSP = Σ duct friction + Σ fitting losses + Σ terminal / plant losses

Where:

= Total (fan) static pressure
= Loss coefficient for a fitting
= Velocity pressure

Derived Equations:

Velocity-pressure form of a fitting loss: Δp_loss = K × p_v

Static left over (negative = over): margin = available − computed

Assumptions & limitations

Every loss is entered by you. This tool holds no duct-friction table, roughness data, fitting database or air-property table, and looks nothing up.
A coefficient without its velocity pressure cannot be turned into a pressure drop, so that item is reported as unresolved rather than given an arbitrary velocity.
Steady-state pressure loss only. Acoustic attenuation, fan noise, duct leakage, system-effect factors, measurement allowance and start-up motor over-sizing are not covered.
The available static is a target you supplied. It is not a rating the tool knows to be safe for any particular system.

Worked example — straight duct plus a bend and a damper

Inputs for the worked example
Straight duct	120 Pa
Bend (K = 0.5, p_v = 100 Pa)	0.5 × 100 = 50 Pa
Damper	30 Pa
Available static	600 Pa

The listed losses sum to 200 Pa against 600 Pa available, leaving 400 Pa — which is where the remaining pressure usually goes, into the terminal units. The bend is the largest single item at 25 % of the total.

Engineering Disclaimer & Verification Notice

This calculator provides preliminary engineering estimates for informational and planning purposes. Actual reverse osmosis / engineering system performance depends on site conditions, feed-water chemistry, membrane characteristics, operating pressure, temperature, recovery limits, fouling/scaling potential, and system design. Verify results using project-specific data, manufacturer projections, and applicable engineering standards before final design or operation.