Get a quote
Home  /  Resources  /  Duty point calculator
Free tool · runs in your browser

Fan duty point calculator

Most fan enquiries arrive without a duty point, or with one taken off an old nameplate. This works it out from what you can actually measure.

  1. 1The airdensity
  2. 2Volumetric flowm³/hr
  3. 3Static pressuremmWG
  4. 4Marginduty point

A duty point is just those two numbers together — how much air and how hard the fan has to push it. Work down the page; each step feeds the next.

1

The air you are moving

This sets the density of the gas, which every later number depends on.

°C
The one figure we will not assume. Hot gas is thinner, so it takes more volume to move the same mass — at 200 °C, about 1.7× as much. Leaving this at ambient is the commonest way a fan ends up undersized.
m
Ahilyanagar 555. Delhi 216, Bengaluru 920.
%
A small effect. Leave it if you do not know.
g/Nm³
Decides which impeller can be used at all. 0 for clean air.
2

Volumetric flow — how much air do you need?

Pick the closest description and answer in things you can measure on site. This step works out the airflow in m³/hr. You do not need to know it already.

One hood, one machine, one room → leave at 1.
1.0 = all at once. 0.5 = half at once, and a smaller fan.
Tell us about the hood
Volumetric flow so far—
3

Static pressure — how hard must the fan push?

Everything the air has to fight through adds resistance. This step adds it up into the static pressure in mmWG.

Describe the index run: the single longest, worst path from the furthest pick-up point all the way to the discharge. Not every branch — just the hardest one, because that is what the fan has to overcome.

Add:
Static pressure so far—
4

Design margin

A little headroom on top of the calculated figures. Always shown separately, never quietly folded in.

Total volumetric flow—from step 2, before margin
Total static pressure—from step 3, before margin
%
%
Duty taken forward—

This calculator runs entirely in your browser. Nothing you type is sent anywhere, and no figure is stored. It gives an indicative duty point and fan family; it is not a quotation and not a performance guarantee. Send us the printed sheet and we will confirm the selection against your actual system.