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.
Everything You Need for Fast HVAC Sizing
Why the Load Comes Before the Equipment
It is a guesswork to buy an air conditioner without determining the load. Under sized and you have to pay more up front and the unit will short cycle and humidity control won't work as the compressor won't run long enough to dehumidify. Oversize it and the nights will be too hot.Make it smaller and the nights will not get down to setpoint when they count.
This is a calculator to estimate the Maximum Cooling load of a single room based on geometry, design conditions, envelope, internal gains and ventilation. It returns sensible and latent heat separately, total load in kW and TR, sensible heat ratio and a suggested nominal with the desired safety value, and round value.All input values are displayed and can be modified, allowing you to see which input is influencing the output.
The glazing area or the outdoor design temperature can be changed and the breakdown changes instantly, which is useful in determining if an outside unit size is defensible prior to selection.It is an approximation for a steady-state situation, rather than an approximation for a time-of-day calculation. To ensure final selection, check performance against ASHRAE Fundamentals, local code and project specification.
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.
What is a heat load calculator?
Is heat load the same as cooling load?
Why are sensible and latent heat calculated separately?
Can I use this calculator for homes and offices?
How accurate is this calculator?
What does TR mean?
Which standards are commonly used for cooling load calculations?
Engineering References
Cooling load estimates should be verified against a recognised calculation method before equipment selection.
