Heating Load Calculator estimates the heating requirements of a space based on either area intensity or a detailed heat loss approach using U-values, temperature difference, and ventilation. It helps architects and HVAC designers size heating systems during early design stages.
About heating load. Heating load is the amount of heat energy required to maintain comfortable indoor conditions during cold weather. It accounts for heat loss through the building envelope (walls, windows, roofs), infiltration and ventilation losses, and is offset by internal gains from people and equipment.
About area intensity method. The area-based method uses a typical heating load intensity (HLI) in watts per square meter (W/m²) or BTU per hour per square foot (BTU/h·ft²). It gives quick results using known reference values from building type and climate. Internal gains and occupants are subtracted to avoid oversizing.
About detailed ΔT + ventilation method. This method uses the building’s thermal transmittance (U·A per area), the indoor-outdoor temperature difference (ΔT), air change rate (ACH), and ceiling height to estimate heat losses. It calculates both transmission losses through the building envelope and ventilation losses from outdoor air, then subtracts internal gains and occupant heat.
About internal gains and occupants. Internal gains are heat from appliances, lighting, and equipment, typically measured in W/m². People also release heat, contributing about 75 W each on average. These reduce the heating load, especially in small or densely occupied spaces.
Calculation. The calculator offers two workflows:
Area Intensity method: Q = A × (HLI − IG) − (P × 75)
ΔT + Ventilation method: Q = A × UA × ΔT + 0.33 × ACH × (A × H) × ΔT − (A × IG + P × 75)
- Example 1: Area = 120 m², HLI = 60 W/m², IG = 5 W/m², People = 3 → 120×(60−5)−3×75 ≈ 6.5 kW.
- Example 2: Area = 150 m², UA = 1.2 W/m²·K, ΔT = 25 °C, ACH = 0.5, Height = 2.7 m, IG = 5 W/m², People = 3 → ≈ 8.9 kW.
- Example 3: Imperial: Area = 1615 ft², UA = 0.21 BTU/h·ft²·°F, ΔT = 45 °F, ACH = 0.7, Height = 9 ft → ≈ 30,300 BTU/h.
Corresponding tools. Use the Cooling Load Calculator to size cooling systems, the HVAC Load Calculator for combined heating/cooling, and the CFM Calculator to determine ventilation airflow rates.
