Sensible Heat Load Calculator
Estimate sensible heat load for your project with our free calculator. Get accurate material quantities, costs, and specifications.
Formula
Q = 1.08 x CFM x Delta-T (at sea level)
Sensible heat (Q) in BTU per hour equals 1.08 multiplied by the air volume flow rate in CFM and the temperature difference in degrees Fahrenheit. The constant 1.08 is derived from the specific heat of air (0.24 BTU/lb/F), standard air density (0.075 lb/ft3), and 60 minutes per hour. An altitude correction factor adjusts for lower air density at elevation.
Worked Examples
Example 1: Office Building Cooling Load
Problem: Calculate the sensible cooling load for 1000 CFM of air cooled from 95 degrees F to 75 degrees F at sea level.
Solution: Delta-T = 95 - 75 = 20 degrees F\nQ = 1.08 x 1000 x 20 = 21,600 BTU/h\nTons = 21,600 / 12,000 = 1.80 tons\nWith 10% safety = 23,760 BTU/h = 1.98 tons
Result: Sensible heat load of 21,600 BTU/h or 1.80 tons of cooling
Example 2: High Altitude Warehouse Heating
Problem: Calculate sensible heat to warm 5000 CFM from 35 degrees F to 70 degrees F at 5000 feet elevation.
Solution: Delta-T = 70 - 35 = 35 degrees F\nDensity ratio at 5000 ft = 0.832\nQ = 0.832 x 1.08 x 5000 x 35 = 157,248 BTU/h\nWith 10% safety = 172,973 BTU/h
Result: Sensible heat load of 157,248 BTU/h (altitude-corrected)
Frequently Asked Questions
What is sensible heat load in HVAC?
Sensible heat load is the amount of thermal energy that must be added or removed from air to change its temperature without changing its moisture content. It is measured in BTU per hour and is the primary factor in sizing air conditioning and heating equipment. Sensible heat differs from latent heat, which involves moisture changes. In a typical cooling application, sensible heat accounts for 60 to 80 percent of the total cooling load.
How is the sensible heat formula derived?
The standard formula Q = 1.08 x CFM x Delta-T combines several constants. The specific heat of air is 0.24 BTU per pound per degree F, standard air density is 0.075 lb per cubic foot, and 60 minutes per hour converts CFM to cubic feet per hour. Multiplying these together gives 0.24 x 0.075 x 60 = 1.08. This constant is only accurate at sea-level standard conditions and must be adjusted for higher altitudes where air density decreases.
Why does altitude affect sensible heat calculations?
At higher altitudes, atmospheric pressure decreases, which reduces air density. Since the sensible heat formula depends on the mass flow rate of air (not just volume), lower density means less mass per cubic foot and therefore less heat transfer per CFM. At 5000 feet elevation, air density is about 83 percent of sea-level density, so the 1.08 factor drops to approximately 0.90. Failing to correct for altitude leads to undersized equipment.
What safety factor should I apply to sensible heat calculations?
Most HVAC engineers apply a 10 to 15 percent safety factor to calculated sensible heat loads to account for uncertainties in occupancy, equipment heat gains, solar gain variations, and aging of the system. Over-sizing beyond 20 percent should be avoided because it causes short cycling in cooling equipment, which reduces dehumidification performance and wastes energy. Variable speed systems can tolerate slightly higher safety factors without the short cycling penalty.
How do I calculate the load-bearing capacity of a beam?
Beam capacity depends on material, cross-section dimensions, span length, and support conditions. For a simple rectangular wood beam, bending strength = (F_b x b x d^2) / 6, where F_b is allowable stress, b is width, and d is depth. Always consult a structural engineer for critical applications.
Is my data stored or sent to a server?
No. All calculations run entirely in your browser using JavaScript. No data you enter is ever transmitted to any server or stored anywhere. Your inputs remain completely private.