Heat Load Calculator
This heat load calculator performs an HVAC load calculation for a room, estimating the cooling it needs from its area, occupants, and equipment. Enter those figures and the heat load calculator returns the load in watts, kilowatts, and BTU per hour, giving you a fast heat load estimation for sizing air conditioning.
Results
The Heat Load Calculator is part of our Cooling & Heating collection. Browse more cooling & heating to size, convert, and check your work alongside this tool.
What the heat load calculator does
The heat load calculator runs an HVAC load calculation that adds up the heat a room gains, so you can size cooling to match. This cooling load calculation counts three sources: the room itself, the people inside, and the equipment running. A good heat load estimation prevents an air conditioner that either struggles or short-cycles.
Heat load calculation formula
The heat load calculator sums a baseline per square meter, the heat from people, and the equipment load:
The baseline of 40 watts per square meter covers a typical sensible load, and each person adds about 100 watts. This heat load calculation formula gives a solid working HVAC load calc for most rooms.
Heat load calculator example
A 25 square meter room with 2 people and 500 watts of equipment, run through the HVAC load calculation:
That heat load is 1.7 kW, or about 5800 BTU/h from the cooling load calculation.
How to use the heat load calculator
Enter the room area in square meters, the number of occupants, and the heat from equipment in watts. The heat load calculation runs at once, giving the total in watts, kilowatts, and BTU per hour. As an AC heat load calculation it points straight to the cooling capacity to buy.
Reading the heat load calculator result
The result is the cooling capacity the room needs. Match an air conditioner to this heat load, rounding up to the nearest available size. Because this is a sensible heat load estimation, add margin for very sunny rooms or spaces with extra equipment beyond what you entered.
When to use the heat load calculator
- Sizing an air conditioner from an HVAC load calculation
- Checking existing cooling with an AC heat load calculation
- Planning cooling for an equipment-heavy office
- Getting a fast heat load estimation before you buy
Common heat load mistakes
- Ignoring equipment. Computers and appliances add real heat load; include their watts.
- Forgetting sun. Sunny rooms need margin above the baseline in the HVAC load calculation.
- Treating it as a full load calc. This is a sensible heat load estimation, not a detailed building study.
Tips for accurate heat load results
- Add all equipment watts for a realistic HVAC load calculation.
- Give sun-facing rooms extra margin over the heat load result.
- Round the cooling load up to the nearest unit size.
What goes into an HVAC load calculation
A room gains heat from more directions than people expect, and a good heat load calculator accounts for the main ones. The building fabric conducts heat through walls and roof, occupants radiate body heat, lighting and equipment convert electricity into warmth, and sunlight pours energy through glass. This HVAC load calculation rolls the common contributors into a working estimate, which covers most rooms while staying quick, unlike a full-blown cooling load calculation that can take hours.
Why an accurate heat load estimation matters
Sizing from a proper heat load calculation protects comfort and efficiency at once. Undersize the cooling and the room never reaches temperature on hot days; oversize it and the unit cools the air fast, shuts off before it removes humidity, and short-cycles wastefully. The AC heat load calculation steers you to the middle, where the cooling matches the room and the equipment runs long, steady cycles that dehumidify properly. That is the whole point of running the HVAC load calc before you buy.
Heat load source chart
Typical contributors in an HVAC load calculation:
| Source | Typical load |
|---|---|
| Room baseline | ~40 W/m² |
| Each person | ~100 W |
| Computer | ~150 W |
Heat Load Calculator FAQ
How do I do an HVAC load calculation?
Add a baseline for the floor area, the heat from occupants, and the equipment load. This heat load calculator uses 40 watts per square meter plus 100 watts per person plus your equipment figure.
What is the heat load calculation formula?
Heat Load = (Area × 40) + (People × 100) + Equipment, in watts. It is a solid sensible heat load estimation; a full cooling load calculation also weighs insulation, glazing, and orientation.
How do I convert the heat load to BTU?
Multiply watts by 3.412. The heat load calculator shows the BTU/h figure automatically alongside watts and kW for the AC heat load calculation.
Is this a full cooling load calculation?
It is a solid working HVAC load calc for a typical room. A detailed cooling load calculation for a whole building weighs many more factors, but this covers most single rooms well.