Room Inputs
Enter gross envelope values carefully. Use opaque wall area excluding windows.
Example Data Table
| Input | Example Value | Purpose |
|---|---|---|
| Room dimensions | 16 ft × 14 ft × 9 ft | Finds area and volume. |
| Outdoor and indoor temperatures | 95°F and 75°F | Sets the sensible temperature difference. |
| Occupants | 2 people | Adds sensible and latent gains. |
| Lighting and equipment | 180 W and 250 W | Converts internal electrical use to heat. |
| Window solar gain | 48 ft², SHGC 0.45, factor 164 | Estimates solar heat through glass. |
| Air leakage and ventilation | 0.35 ACH and 30 CFM | Adds sensible and moisture loads. |
| Expected estimate | About 9,682 Btu/h | Includes a 10% design margin. |
Formula Used
The calculator uses practical steady-state heat-gain relationships. Values are estimates and should be checked against local design conditions.
One refrigeration ton equals 12,000 Btu/h. Nominal equipment capacity is rounded upward to the next half ton.
How to Use This Calculator
- Measure the room length, width, and ceiling height.
- Set realistic outdoor design and indoor target temperatures.
- Enter envelope areas and U-values. Exclude windows from opaque wall area.
- Add occupants, lighting, equipment, ventilation, and infiltration assumptions.
- Use humidity difference for latent airflow estimates.
- Choose a modest margin, then select the next suitable nominal capacity.
- Review the component table before using the result for equipment planning.
Cooling Load Basics
A cooling load is the heat a room must remove during design conditions. It is more than room size. Sunlight, people, lights, appliances, fresh air, and construction all matter. Western glass can make a small room load heavily. The calculator combines these gains. It separates sensible heat from latent heat. Sensible heat changes air temperature. Latent heat comes from moisture. Both affect comfort.
Heat Sources Inside a Room
Internal gains come from people and equipment. Occupants release heat and moisture. Lighting changes electrical watts into heat. Computers, appliances, and motors produce heat. Enter realistic operating watts. Some equipment runs intermittently. Consider expected use during the hottest period. This avoids an inflated result from a rarely used load.
Envelope and Solar Gains
Walls, roofs, and windows transfer outdoor heat inward. Their effect depends on area, insulation, and temperature difference. Lower U-values indicate better insulation. Solar gain through glass can dominate afternoon loads. Window area, shading, orientation, and glazing change this effect. This method uses a solar factor and glass coefficient. Choose values that match expected exposure. External shading can reduce loads far more effectively than interior blinds.
Ventilation and Moisture
Warmer outdoor air adds sensible heat. It adds latent heat when outdoor air contains more moisture. Infiltration is uncontrolled air leakage. Ventilation is intentional outdoor airflow. Both are calculated from airflow and humidity difference. Tight construction can reduce infiltration. Do not remove required outdoor air. Use local ventilation requirements and verified moisture conditions for final design.
Using Results Safely
The result is an early estimate, not a stamped design. Add reasonable margin for uncertainty. Do not use margin to hide poor assumptions. Check every area, U-value, wattage, and airflow entry carefully. Compare results with equipment capacity at actual conditions. Duct losses, distribution balance, compressor performance, and climate data can change final selection. Consult a qualified designer for permit work, critical spaces, or complex buildings.
Planning Better Systems
Use the estimate to compare insulation, shading, glazing, and equipment choices. Reduce loads before choosing a larger unit. Better envelopes can improve comfort and reduce operating cost. Divide buildings into separate zones when exposure or schedules differ. Confirm that selected equipment can handle sensible and latent demand. Keep calculation records with project assumptions. Clear records make later reviews and revisions easier.
Frequently Asked Questions
1. What does this calculator estimate?
It estimates a room’s sensible and latent cooling demand from envelope heat, sunlight, people, electrical loads, ventilation, infiltration, and a selectable margin.
2. Is room area enough for equipment sizing?
No. Floor area omits sun exposure, insulation, glass, occupancy, moisture, ventilation, and equipment heat. Those factors can change capacity substantially.
3. What is sensible cooling load?
Sensible load is heat that changes air temperature. Walls, solar gain, lights, equipment, and warm outdoor air are common sensible sources.
4. What is latent cooling load?
Latent load is moisture removal. People and humid outdoor air create latent demand. It affects comfort even when the thermostat temperature seems correct.
5. What is a U-value?
A U-value describes heat transmission through a building element. Lower values generally mean better insulation and lower conductive heat gain.
6. Should window area be included in wall area?
No. Enter opaque wall area after subtracting window area. Windows are calculated separately because their conduction and solar gains differ.
7. How do I choose the solar factor?
Use a value reflecting window orientation, shading, season, and local design conditions. Higher exposure needs a larger solar factor. Professional design tools refine this value.
8. Why is design margin included?
A modest margin addresses uncertainty in inputs and operating conditions. Excessive margin can cause short cycling, poor dehumidification, and inefficient operation.
9. What is ACH?
Air changes per hour estimates uncontrolled leakage. It describes how many room volumes of air enter or leave during one hour.
10. Can I use this for an entire building?
Use it room by room for early comparisons. Whole-building selection needs zone diversity, duct heat, system performance, schedules, and local climate analysis.
11. When should I seek professional review?
Seek review for permits, critical occupancies, complex glazing, specialized equipment, humid climates, or any final equipment purchase. Good inputs improve estimates and support safer cooling choices.