Skip to main content
Calcimator

Air Balance Calculator

Calculate building air balance, pressurization status, and required adjustments from supply, return, exhaust, and outside air flows.

Inputs

CFM
CFM
CFM
CFM

ASHRAE 62.1 Table 6.2.2.1: offices 5 CFM/person+0.06 CFM/ft²; classrooms 10 CFM/person+0.12 CFM/ft²

CFM

Results

Net Air Balance

500 CFM

Pressurization

1 (1=Positive, 2=Negative, 3=Neutral)

Balance Ratio110%
Adjustment Needed-500 CFM
How to Use This Calculator
  1. Enter Supply Air, Return Air, and Exhaust Air.
  2. Set Outside Air and Transfer Air.
  3. Review Net Air Balance (CFM) and Pressurization ((1=Positive, 2=Negative, 3=Neutral)).
  4. Use Balance Ratio (%) and Adjustment Needed (CFM) to inform your decision.

How the result changes with Supply Air

Supply AirNet Air BalancePressurization
50,00045,500 CFM1 (1=Positive, 2=Negative, 3=Neutral)
175,000170,500 CFM1 (1=Positive, 2=Negative, 3=Neutral)
325,000320,500 CFM1 (1=Positive, 2=Negative, 3=Neutral)
450,000445,500 CFM1 (1=Positive, 2=Negative, 3=Neutral)

What each input means

Supply Air
Total supply air delivered to the space from AHU(s).
Return Air
Total return air drawn back to the AHU(s) from the space.
Exhaust Air
Total exhaust air removed from the building (restrooms, kitchen hoods, etc.).
Outside Air
Fresh outside air introduced through the AHU or dedicated unit per ASHRAE 62.1 minimum OA requirements. Offices: 5 CFM/person + 0.06 CFM/ft²; classrooms: 10 CFM/person; retail: 7.5 CFM/person + 0.12 CFM/ft².
Transfer Air
Air transferred from adjacent zones through ducts, door undercuts, etc.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Supply Air = 5000, Return Air = 4500, Exhaust Air = 500, Outside Air = 500 = 5 input(s) provided
  2. Calculate Net Air Balance
    Net Air Balance
    500 = 500
  3. Calculate Pressurization
    Pressurization
    1 = 1
  4. Calculate Balance Ratio
    Balance Ratio
    110 = 110
  5. Calculate Adjustment Needed
    Adjustment Needed
    -500 = -500

Engine last updated . Checked against 3 independently-derived tests — how we verify calculators.

Related Calculators

The questions that sit next to this one — chosen by subject, including calculators filed under a different category.

HVAC

Duct Sizing Calculator

Size round or rectangular ductwork using the equal friction method based on CFM and desired friction rate.

HVAC

Ventilation Rate Calculator

Calculate required outdoor air ventilation rates per ASHRAE Standard 62.1 based on occupancy and space type.

Hvac Controls

Commissioning Schedule Calculator

Cx timeline from point count and system complexity.

HVAC

BTU Calculator

Calculate heating and cooling BTU requirements for your room or home. Determine the right AC tonnage and furnace size based on room dimensions, insulation, and climate.

More in Construction & Building Trades.