About this calculator
This calculator determines the Air Sensible Heat Factor, which relates airflow (CFM), temperature difference (ΔT), and sensible heat load (BTU/hr) in the formula BTU/hr = CFM × Cs × ΔT. Enter the site altitude and the air's humidity ratio to get Cs corrected for both. Use it in place of the textbook 1.08 when the site is well above sea level or the air is humid.
Use when You need to determine Cs for sensible heat load calculations at a given altitude and humidity ratio.
Formula Cs = 60 × 0.075 × (0.24 + 0.45 × W) × Density Factor
Variables
Altitude Elevation above sea level in feetHumidity Ratio W Mass of water vapor per mass of dry air (lb/lb)
Altitude (ft)
Installation altitude — autofilled from weather station
Humidity Ratio W (lb/lb)
W = 0.01 at approximately 75°F / 50% RH
Air Sensible Heat Factor 1.1002

What is the Air Sensible Heat Factor?

The Air Sensible Heat Factor is a coefficient used in the sensible heat equation BTU/hr = CFM × Cs × ΔT. It combines the effects of air density, specific heat of moist air, and unit conversion into a single factor. Cs is calculated as: Cs = 60 × 0.075 × (0.24 + 0.45 × W) × Density Factor, where 60 converts minutes to hours, 0.075 lb/ft³ is standard sea-level air density, (0.24 + 0.45 × W) is the specific heat of moist air (BTU/lb-°F), W is the humidity ratio in lb/lb, and the Density Factor corrects for altitude. At sea level with completely dry air (W=0), Cs = 1.08 — the classic constant used in simplified heating and cooling calculations. At W=0.01 (approximately 75°F / 50% RH, typical design conditions), Cs ≈ 1.10. At higher altitudes, Cs decreases proportionally to the reduction in air density, about 3.5% per 1,000 ft of elevation. This is not the sensible heat ratio (SHR), which is the sensible share of a total cooling load.

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Cooling Density Factor

Sensible + Latent CFM