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Calcimator

Kitchen Ventilation Makeup Air Calculator

Size makeup air units based on exhaust CFM, pressurization balance, and climate heating requirements.

Inputs

%

Results

Makeup Air CFM

3,400

Pressure Deficit (CFM)600
Negative Pressure (%)15
Heating Capacity (BTU/hr)201,960
Est. Monthly Heating Cost ($)$727.00
MAU Fan HP1.25
MAU Duct Diameter (in)26
Pressure StatusSlight negative - ideal for kitchen isolation
How to Use This Calculator
  1. Enter the total exhaust CFM from all kitchen hoods.
  2. Set makeup air as a percentage of exhaust (80-90% is typical to maintain slight negative pressure).
  3. Enter the winter design outside temperature and desired supply air temperature.
  4. Review makeup air CFM and heating BTU/hr to size the makeup air unit.
  5. Use the estimated monthly heating cost for utility budget planning.

How the result changes with Total Exhaust CFM

Total Exhaust CFMMakeup Air CFM
5,0904,327
17,56514,930
32,53527,655
45,01038,259

What each input means

Total Exhaust CFM
Total kitchen exhaust airflow that the makeup air must replace.
Makeup Air % of Exhaust
Percentage of exhaust to replace. 80-90% is typical (creates slight negative pressure to contain cooking odors).
Winter Design Temp (°F)
Coldest outside temperature for heating capacity sizing.
Supply Air Temp (°F)
Desired temperature of makeup air entering the kitchen. Typically 60-70°F.

What each result means

Makeup Air CFM
Volume of makeup air to supply.
Pressure Deficit (CFM)
Exhaust minus makeup — creates negative pressure in kitchen.
Negative Pressure (%)
Percentage of exhaust not replaced. 10-20% is ideal.
Heating Capacity (BTU/hr)
Gas-fired heating capacity needed to temper makeup air.
Est. Monthly Heating Cost ($)
Estimated gas heating cost at $1.20/therm, 10 hrs/day.
MAU Fan HP
Makeup air unit fan motor horsepower.
MAU Duct Diameter (in)
Main makeup air duct diameter at 1000 FPM (low noise).

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Total Exhaust CFM = 4000, Makeup Air % of Exhaust = 85, Winter Design Temp (°F) = 10, Supply Air Temp (°F) = 65 = 4 input(s) provided
  2. Calculate Makeup Air CFM
    Makeup Air CFM
    3400 = 3400
  3. Calculate Pressure Deficit
    Pressure Deficit
    600 = 600
  4. Calculate Negative Pressure
    Negative Pressure
    15 = 15

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