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Ventilation Rate Calculator

Work out ventilation rate instantly with clear inputs, formula shown and shareable results.

About Ventilation Rate Calculator

The ventilation rate procedure splits outdoor air demand into a people term and a building term: Vbz = Rp x Pz + Ra x Az. The people term dilutes occupant-generated contaminants such as carbon dioxide and odour; the area term handles emissions from furnishings and finishes that continue whether the space is occupied or not.

Formula

Breathing zone airflow

Vbz = Rp x Pz + Ra x Az

Rp
CFM per person
Pz
Zone population
Ra
CFM per ft²
Az
Zone floor area

Worked example

With the default values below, Ventilation Rate Calculator returns Breathing zone outdoor air of 245. Change any input above and every figure here is recalculated in your browser.

Inputs used

Design occupancyminimum 1
25
Zone floor areaminimum 1 ft²
2,000 ft²
Airflow per person (Rp)minimum 0 CFM/person
5 CFM/person
Airflow per area (Ra)minimum 0 CFM/ft²
0.06 CFM/ft²

Results

Breathing zone outdoor air
245 CFM
People component
125 CFM
Area component
120 CFM
Effective rate per person
9.80 CFM/person

Step by step

  1. 1Values used
  2. 2Breathing zone airflow
  3. 3Breathing zone outdoor air= 245 CFM
  4. 4People component= 125 CFM
  5. 5Area component= 120 CFM
  6. 6Effective rate per person= 9.80 CFM/person

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Preliminary estimate only. Confirm required rates and zone effectiveness against the ventilation standard adopted by your local code.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Preliminary estimate only. Confirm required rates and zone effectiveness against the ventilation standard adopted by your local code.

Frequently Asked Questions

How is the Ventilation Rate figure worked out?

Vbz = Rp x Pz + Ra x Az. The ventilation rate procedure splits outdoor air demand into a people term and a building term: Vbz = Rp x Pz + Ra x Az.

Do these numbers go straight to the air handler?

No. The breathing zone value is divided by zone air distribution effectiveness and then combined across zones to give the outdoor air intake flow at the unit.

What values do I need to enter?

This calculator takes 4 inputs: Design occupancy, Zone floor area, Airflow per person (Rp), Airflow per area (Ra). The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.

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