Load Calculation Rules of Thumb

At cfm we like rules of thumb. We have rules of thumb for airflow, air distribution, cooling capacities and more.

Today we provide you with a “Square Feet per Ton” cooling rule of thumb guide based on some common applications. 

Note: your project or application may vary widely from the following. This is for informational purposes only. 

Each rule of thumb is based on the following:

  • 98/78 db/wb summer ambient design temperature
  • 0 db/wb winter ambient design temperature
  • 72 degF space temperature at 55% Rh
  • Windows: double pane with mix of shaded and unshaded
  • Insulation: R-10 walls, R-19 ceiling
  • Average lighting
  • Fresh air requirements from the 2018 IMC ventilation tables

Office space with 8′ ceilings

  • 373 square feet per ton cooling
  • 20 btuh per square foot heating
  • 1.1 cfm per square foot
  • 0.50 cooling tons per person

Retail sales floor with 14′ ceilings

  • 321 square feet per ton cooling
  • 34 btuh per square foot heating
  • 1.2 cfm per square foot
  • 0.20 cooling tons per person

Religious worship with 18′ ceilings*

  • 115 square feet per ton cooling
  • 75 btuh per square foot heating
  • 3.9 cfm per square foot
  • 0.08 cooling tons per person

Classrooms with 8′ ceilings

  • 213 square feet per ton cooling
  • 48 btuh per square foot heating
  • 1.9 cfm per square foot
  • 0.15 cooling tons per person

Restaurant dining room with 8′ ceilings*

  • 132 square feet per ton cooling
  • 73 btuh per square foot heating
  • 3.1 cfm per square foot
  • 0.11 cooling tons per person

Theater or multiuse assembly with 14′ ceilings*

  • 107 square feet per ton cooling
  • 85 btuh per square foot heating
  • 3.7 cfm per square foot
  • 0.10 cooling tons per person

*Design tip: on applications that approach 3+ cfm per square foot, it might make sense to add an ERV. In our next article we will explain why adding an ERV could be beneficial, how it affects air distribution, and if they make financial sense. Subscribe here to get a copy sent direct to your inbox!

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Brad Telker
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