This cooling coil calculator finds the total, sensible, and latent capacity a coil must deliver to move air from its entering condition to its leaving condition. Enter the entering and leaving dry-bulb and wet-bulb temperatures, the airflow in CFM, and the site elevation; the tool returns capacity in BTU/h and tons, the sensible heat ratio (SHR), the moisture removed in lb/hr and gallons per hour, and an optional face velocity from the coil dimensions.
Working from the full psychrometric state of each air stream — not just a temperature difference — lets the tool separate sensible cooling from the latent (dehumidification) load. That split drives coil row and circuit selection, chilled-water flow, and reheat strategy, so getting it right early avoids undersized coils and humidity-control problems downstream.
Humidity ratio W comes from each dry-bulb/wet-bulb pair through the ASHRAE Handbook—Fundamentals (2021) Chapter 1 wet-bulb equation, and h = 0.240·T + W·(1061 + 0.444·T), at the standard-atmosphere barometric pressure for your elevation. The airflow is taken as actual CFM at the entering condition, so the dry-air mass flow uses the entering specific volume vin = 0.370486·(T + 459.67)·(1 + 1.607858·W)/P rather than the standard-air 0.075 lb/ft³. Standard-air shortcuts (4.5 × CFM × Δh, 1.08 × CFM × ΔT) read about 4 % higher at 80 °F entering air. Sensible heat uses the moist-air specific heat 0.240 + 0.444·W, so sensible plus latent equals the enthalpy change exactly. 12,000 BTU/h equals one ton of refrigeration, and 8.34 lb/gal converts condensate mass to gallons per hour.
Frequently Asked Questions
How is total cooling coil capacity calculated?
Total capacity is the air mass flow times the enthalpy drop across the coil: BTU/h = mass flow (lb/hr) times (h entering minus h leaving). Mass flow comes from the airflow in CFM times 60 times the actual air density, and enthalpy is found from each air stream's dry-bulb and humidity ratio. Dividing by 12,000 converts BTU/h to tons of refrigeration.
What is sensible heat ratio (SHR) and why does it matter?
SHR is the sensible capacity divided by the total capacity. It tells you how much of the coil's work goes to lowering temperature versus removing moisture. A high SHR near 0.9 means mostly dry-cooling, while a low SHR near 0.6 means heavy dehumidification. Matching coil SHR to the space load is essential for humidity control.
How does elevation affect the coil capacity?
Higher elevation lowers barometric pressure and therefore air density, so a given CFM carries less mass. Pressure also changes the humidity ratio a wet-bulb reading implies, so at altitude the same entering and leaving temperatures mean more moisture removed per pound of air. This tool corrects barometric pressure for elevation and uses the actual dry-air density at entering conditions rather than the standard 0.075 lb/ft3, which keeps capacity and moisture-removal numbers consistent at altitude.
What is a typical coil face velocity?
Cooling coils are usually designed for a face velocity of about 400 to 500 fpm. Below roughly 300 fpm the coil is oversized for the airflow; above about 500 fpm condensate carryover becomes a concern, and above roughly 550 to 600 fpm water can be blown off the fins and carried downstream unless eliminators are used. Enter both coil face dimensions and the tool flags velocities below 300 or above 500 fpm. These are typical design-practice limits, not code requirements.
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