Free HVAC Heat Load Calculator
Everything You Need for Fast HVAC Sizing
BuildMeP Engineering Tool
Heat Load Calculator
Estimate a room’s peak cooling load with a transparent sensible and latent breakdown.01 · SetupProject / location⌄
02 · GeometryRoom dimensions⌄
03 · ConditionsIndoor and outdoor design conditions⌄
Indoor design
Outdoor design editable example
Use coincident project design conditions. Defaults are preliminary hot-climate examples, not certified weather data.
04 · EnvelopeConstruction / exposure⌄
05 · Internal loadsPeople, lighting and equipment⌄
People
Electrical and process loads
06 · AirsideOutdoor air and sizing⌄
Outdoor-air rates are user inputs. Confirm them against the applicable project code and system ventilation calculation.
Transparent by design
What the estimate includes
Envelope
Opaque and glazed conduction using U × A × ΔT, plus a simplified sol-air allowance.Solar
Glazing area × SHGC × shading × orientation-specific incident solar allowance.Internal loads
People sensible/latent gains, lighting, equipment and editable process loads.Outdoor air
Ventilation and infiltration loads from coincident dry bulb and relative humidity.This preliminary estimator is not a substitute for an approved hourly calculation using ASHRAE Heat Balance/RTS, CIBSE admittance, or the project-required method. Verify thermal storage, hourly coincidence, duct and fan heat, system diversity, plenums, thermal bridges and equipment performance separately.
Free HVAC Heat Load CalculatorSelecting the correct air conditioning capacity starts with an accurate cooling load calculation. Oversized equipment increases installation costs and causes frequent cycling, while undersized systems struggle to maintain comfortable indoor conditions.The BuildMEP HVAC Heat Load Calculator helps engineers, HVAC technicians, facility managers, students, and homeowners estimate room cooling loads quickly using practical engineering assumptions. The calculator provides sensible heat, latent heat, total cooling load, and the recommended nominal cooling capacity in both kilowatts (kW) and tons of refrigeration (TR).Simply enter your room dimensions, indoor and outdoor design conditions, occupancy, lighting, equipment, and ventilation details. The calculator updates instantly, making it useful for preliminary HVAC design, equipment selection, and educational purposes.Although this tool is designed for fast and practical estimates, final HVAC system sizing should always follow detailed engineering calculations based on recognized standards such as ASHRAE Fundamentals and project-specific requirements.
How This Heat Load Calculator Works
Selecting the right air conditioning capacity begins with estimating the total cooling load of the space. The BuildMEP HVAC Heat Load Calculator analyzes the major sources of heat gain and combines them to estimate the required cooling capacity.
Simply enter your project details, room dimensions, indoor and outdoor design conditions, occupancy, lighting, electrical equipment, windows, building envelope, and ventilation information. The calculator processes these inputs instantly and displays the estimated sensible heat, latent heat, total cooling load, cooling capacity in kilowatts (kW) and Tons of Refrigeration (TR), sensible heat ratio (SHR), and recommended nominal air-conditioning capacity.
This calculator is intended for preliminary HVAC design, equipment selection, educational purposes, and quick engineering estimates. While it provides practical results for most applications, final system sizing should always be verified using detailed engineering calculations and applicable standards such as ASHRAE Fundamentals, local building codes, and project-specific requirements.
How the Heat Load Calculation Works
The BuildMEP Heat Load Calculator follows a structured engineering workflow to estimate the cooling load and recommend the appropriate air-conditioning capacity.
What Is Heat Load?
Heat load, also known as cooling load, is the total amount of heat that must be removed from a room or building to maintain the desired indoor temperature and humidity. HVAC engineers use cooling load calculations to determine the correct air conditioning capacity required for comfortable indoor conditions.
Heat enters a building from many different sources including outdoor weather, solar radiation through windows, occupants, lighting, electrical equipment, ventilation air, roofs, walls and other building components. An HVAC system must remove all of these heat gains to keep the space comfortable.
Why is Heat Load Calculation Important?
An oversized air conditioner increases installation cost, consumes more energy and may short-cycle without properly removing humidity. An undersized unit may run continuously and still fail to maintain the required indoor temperature. Performing a heat load calculation helps select equipment that delivers better comfort, improved efficiency and longer service life.
🌡 Outdoor Heat Gain
Heat entering through walls, roofs, windows and solar radiation.
👥 Occupants
People generate both sensible and latent heat depending on activity level.
💡 Lighting
Lighting fixtures convert electrical power into heat inside the room.
🖥 Equipment
Computers, printers, appliances and machinery contribute internal heat gains.
🌬 Ventilation
Fresh outdoor air introduces both sensible and latent cooling loads.
💧 Humidity
Moisture removal contributes to the latent heat portion of the cooling load.
Frequently Asked Questions
Find answers to common questions about HVAC heat load calculations, cooling capacity and air-conditioning system sizing.