The short answer
Cooling load is the heat—and often moisture—that must be removed at the cooling design condition. Heating load is the heat that must be added at the heating design condition. A building can need much more cooling than heating, or the opposite, depending on climate, envelope, glazing, schedules, and ventilation.
What changes between the calculations
| Question | Cooling load | Heating load |
|---|---|---|
| Design objective | Remove sensible heat and manage latent moisture where applicable. | Replace heat lost to outdoors and unconditioned spaces. |
| Outdoor condition | High dry-bulb temperature and humidity can both matter. | Low outdoor temperature drives heat loss. |
| Solar effect | Often a major peak contributor through glazing and roofs. | May offset loss at a particular time but should not be assumed available at the heating peak. |
| Internal gains | People, lighting, and equipment add to the removal requirement. | They may reduce net heating demand when they occur, but schedules matter. |
| Outdoor air | Adds sensible and potentially latent load. | Adds sensible heating load; moisture effects depend on the conditioning strategy. |
| Equipment check | Compare the calculated cooling requirement with delivered capacity at design conditions. | Compare the heating requirement with delivered heating capacity at design conditions. |
A small airflow example
For sensible heat only in U.S. customary units, BTU/h = 1.08 × CFM × ΔT°F. If 100 CFM of outdoor air is 30°F colder than the indoor target, the sensible heating effect is approximately 1.08 × 100 × 30 = 3,240 BTU/h. That same relationship does not determine cooling latent load, so it cannot by itself size cooling equipment.
Which result should guide the decision?
Use cooling load when selecting and checking the cooling side of the system, humidity approach, and cooling airflow. Use heating load when checking winter capacity and distribution. Do not choose a system from whichever number looks larger without checking manufacturer performance data, zoning, duct losses, ventilation, local requirements, and the project’s detailed design method.
Where estimates go wrong
- Assuming an equipment nameplate tonnage applies at all outdoor conditions.
- Ignoring latent cooling and treating all cooling load as sensible.
- Using a cooling result to size heating equipment, or vice versa.
- Counting the same solar, people, or ventilation effect twice.
FAQ
Are cooling load and heating load both measured in BTU/h?
They can both be expressed in BTU/h, kW, or other rates of heat transfer. The matching unit does not make their inputs or equipment checks interchangeable.
Why can heating load be larger in a small building?
A compact building in a cold design climate can have substantial envelope and outdoor-air heat loss even when its cooling-related solar and internal gains are modest.
Related tools and guides
- HVAC Load Calculator — compare preliminary cooling and heating components in one workflow.
- BTU to Tons Calculator and CFM Calculator.
- Cooling Load Calculation Explained and Heating Load Calculation Explained.