Cooling Density Factor

A density correction factor adjusts HVAC capacity calculations for air density changes caused by altitude. At higher elevations, air is less dense, which reduces the mass flow rate through equipment for a given volumetric airflow (CFM). This means each CFM carries less heat, so the air-side capacity of a given airflow drops in proportion to density. The correction factor is calculated using the barometric formula: Factor = (1 - 0.00000687 × Altitude)^5.256, where Altitude is the elevation in feet above sea level. At 5,000 feet, the factor is approximately 0.83, meaning a given CFM carries roughly 83% of the heat it would at sea level. Gas burners and refrigerant coils also have their own manufacturer altitude derates, which should be used where published. Most HVAC manufacturers rate equipment at standard conditions (sea level, 70°F), so this correction must be applied during equipment selection for any installation above approximately 1,000 feet to avoid undersizing.