HVAC Load Calculator calculates heating and cooling loads for residential, commercial, or industrial spaces. Enter floor area, occupancy, and insulation data for HVAC sizing, and understand the role of units like watts, kilowatts, and BTU/h.
About watts (W). The watt (W) is the SI unit of power, defined as one joule per second. In HVAC, loads are often expressed as watts per square meter (W/m²) to show how much heating or cooling is required for each unit of area.
About kilowatts (kW). Large heating and cooling loads are typically expressed in kilowatts (kW). One kilowatt equals 1,000 watts. HVAC equipment such as boilers, chillers, or air conditioners is usually rated in kW to simplify comparison of system capacities.
About BTU/h. The British Thermal Unit per hour (BTU/h) is commonly used in Imperial systems to measure heating and cooling power. One BTU/h represents the heat required to raise the temperature of one pound of water by 1°F per hour. Air conditioners are often rated in BTU/h or “tons” (1 ton = 12,000 BTU/h).
Calculation. Heating and cooling loads are determined by multiplying the floor area with intensity factors and adding internal gains.
Cooling Load = (Cooling Intensity × Area) + (Internal Gains × Area) + (Occupants × 75 W)
Heating Load = (Heating Intensity × Area)
Convert results between kW and BTU/h: 1 kW = 3,412 BTU/h
- Example 1: A 120 m² office with 100 W/m² cooling intensity, 12 W/m² equipment, and 4 people → ≈17.3 kW cooling load.
- Example 2: The same office with 60 W/m² heating intensity → ≈7.2 kW heating load.
- Example 3: A 5 kW cooling load = 5 × 3,412 = 17,060 BTU/h.
Corresponding tools. To calculate HVAC loads by volume (using ceiling height and W/m³ values), try the HVAC Volume Load Calculator. You can also explore other HVAC and electrical calculators for duct sizing, voltage drop, and related MEP design tasks.
