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Calculation Machine

Fresh Air CFM per Person Calculator

Outdoor air rate for occupied spaces.

Reviewed by James Whitfield · How we check our maths

Your values

ⓘ Live results

Results
Outdoor air required
190 CFM
Per person
9.5 CFM
Per square foot
0.127
In L/s
90

Working

  1. 15 x 20 + 0.06 x 1,500 = 190 CFM

Quick answer

Outdoor air is the sum of a per-person rate and a per-square-foot rate for the space type.

The formula

Vbz = Rp x people + Ra x area

Worked example

Worked example

Using the values the calculator loads with.

Inputs

  • Occupants20
  • Floor area1500 sq ft
  • Space typeOffice (5 + 0.06)

Result

  • Outdoor air required190 CFM
  • Per person9.5 CFM
  • Per square foot0.127
  • In L/s90

How to use the Fresh Air CFM per Person Calculator

  1. 1Count design occupancy, not the number of desks.
  2. 2Enter the floor area served by the same air handler.
  3. 3Divide by the ventilation efficiency if you use a single-zone economiser.

Frequently asked questions

Does CO2 control replace this?

Demand control can modulate down to the area component, but the design value still governs equipment size.

Why per area too?

Building materials and furnishings off-gas regardless of occupancy.

About this calculator