HVAC Load Calculator

Free online HVAC load calculator to estimate heating and cooling requirements for buildings. Calculate sensible and latent heat loads for proper HVAC system sizing.

The HVAC Load Calculator helps you estimate the total heating and cooling load for a room or building. Calculate sensible heat, latent heat, and total BTU requirements based on room characteristics, occupancy, and environmental factors.

What is HVAC Load Calculation?

HVAC load calculation is the process of determining the amount of heating and cooling energy required to maintain comfortable indoor conditions in a building. It's the foundation of proper HVAC system design. Load calculations account for building size, insulation quality, window area, occupancy, equipment heat, sun exposure, and local climate. Accurate calculations prevent oversized systems (which waste energy and short-cycle) or undersized systems (which can't maintain comfort). Professional calculations follow ACCA Manual J standards.

How to Use the HVAC Load Calculator

Enter room dimensions: length, width, and height in feet or meters
Specify number of occupants in the space
Select insulation quality: poor, average, good, or excellent
Choose sun exposure level: shaded, average, or sunny/high exposure
Select climate zone: cold, moderate, or hot/humid
Click Calculate to see cooling and heating load requirements
Results show total BTU/hr and recommended AC capacity in tons

Heat Load Components

Sensible heat: Temperature-based heat gain/loss through walls, roof, windows
Latent heat: Moisture from people, cooking, infiltration
Occupant heat: ~400 BTU/hr per person (250 sensible, 150 latent)
Equipment/lighting: Varies by wattage and usage
Solar gain: Through windows, varies by orientation and shading
Infiltration: Air leaks through building envelope

HVAC Load Calculation Formulas

1. Room Volume

Volume (cu ft) = Length × Width × Height

2. Sensible Heat Load

Q_sensible = U × A × ΔT + Solar Gain + Occupant Heat + Equipment Heat

3. Latent Heat Load

Q_latent = Occupant Moisture + Infiltration Moisture + Internal Sources

4. Total Cooling Load

Total BTU/hr = Sensible Load + Latent Load + Safety Factor (10-20%)

Factors Affecting HVAC Load

Building Envelope: Wall/roof U-values, insulation R-values, thermal mass

Windows: Area, orientation, shading, glazing type (single/double pane)

Infiltration: Air leakage through cracks, construction quality

Occupancy: Number of people, activity level, schedule

Internal Gains: Lighting, appliances, computers (3.41 BTU/hr per Watt)

Ventilation: Fresh air requirements, outdoor air temperature/humidity

Climate Zone Considerations

Hot/Humid: Higher cooling load, dehumidification critical, insulation less important

Moderate: Balanced heating and cooling, good insulation recommended

Cold: Heating load dominant, excellent insulation essential, air sealing critical

HVAC Sizing Tips

Always add 10-20% safety margin to calculated load
Never size based on square footage alone - many factors affect load
Oversized AC units short-cycle and don't dehumidify properly
Undersized units run constantly and can't maintain temperature
Improve insulation and air sealing before upsizing HVAC
Consider zoning for large or multi-story homes
Professional Manual J calculations are recommended for new installations
Local climate and weather extremes should be considered

Useful Conversions

1 Ton = 12,000 BTU/hr cooling capacity

Rule of thumb: 20-30 BTU/hr per square foot (varies by climate)

1 Watt = 3.41 BTU/hr heat output

Common HVAC Sizing Mistakes

Using square footage only without considering ceiling height, insulation, windows
Ignoring sun exposure and window orientation
Not accounting for occupancy and internal heat sources
Oversizing "to be safe" - causes short cycling and poor humidity control
Not considering ductwork design and static pressure
Using old rules of thumb instead of proper load calculations
Forgetting to add safety margin for extreme weather days

HVAC Load Calculator

Room Information

Building Factors