Enter Cooling Load Details
This tool gives a preliminary compressor size. Final HVAC selection should follow local codes, equipment data, duct design, and a professional load calculation.
Example Data Table
| Room Type | Area | Windows | Occupants | Estimated Size | Approx. Tons |
|---|---|---|---|---|---|
| Small bedroom | 150 sq ft | 20 sq ft | 1 | 6,000 to 9,000 BTU/hr | 0.50 to 0.75 |
| Living room | 350 sq ft | 55 sq ft | 3 | 18,000 to 24,000 BTU/hr | 1.50 to 2.00 |
| Open office | 900 sq ft | 120 sq ft | 8 | 48,000 to 60,000 BTU/hr | 4.00 to 5.00 |
| Retail zone | 1,500 sq ft | 220 sq ft | 15 | 72,000 to 90,000 BTU/hr | 6.00 to 7.50 |
Formula Used
The calculator uses a simplified physics-based cooling load method. It combines envelope heat gain, people load, window gain, equipment heat, infiltration load, duct loss, and safety margin.
Area: Area = Length × Width × Number of zones
Volume: Volume = Area × Ceiling height
Envelope load: Area × 18 × Height factor × Climate × Insulation × Sun × Floor factor
People load: Occupants × 600 BTU/hr
Window load: Window area × Window BTU factor × Sun factor
Appliance load: Watts × 3.412142
Infiltration load: 1.08 × CFM × Temperature difference
CFM: Room volume × ACH ÷ 60
Recommended capacity: Subtotal + Duct loss + Safety margin
Tons: BTU/hr ÷ 12,000
Compressor watts: BTU/hr ÷ EER
Horsepower: Watts ÷ 746
COP: EER ÷ 3.412142
How to Use This Calculator
Enter the room length, width, and ceiling height first. Add the number of similar zones if the same compressor will serve more than one room. Then choose climate, insulation, sunlight, floor condition, and humidity. Add people, window area, appliance watts, air leakage, duct loss, and safety margin.
Use EER when you want electrical power, horsepower, and current estimates. A higher EER means lower compressor input power for the same cooling capacity. Press the calculate button. The result appears above the form and below the header. Use the CSV or PDF buttons to save the sizing report.
Physics of AC Compressor Sizing
Cooling Capacity Matters
An air conditioner removes heat from indoor air. The compressor drives the refrigerant cycle. It raises refrigerant pressure and temperature. This makes heat rejection possible at the outdoor coil. A correct compressor size helps the system cool steadily. It also protects comfort, moisture control, and energy use.
Heat Load Sources
A room gains heat in many ways. Walls, ceilings, and floors conduct heat. Windows admit solar radiation. People release sensible and latent heat. Lights and appliances convert electricity into heat. Outdoor air also enters through cracks, doors, and ventilation paths. Each source adds to the total cooling load.
Why Tonnage Is Used
Cooling capacity is often shown in BTU per hour. It is also shown in tons. One ton equals 12,000 BTU per hour. A small room may need less than one ton. A large open zone may need several tons. The calculator converts BTU per hour into tons for easy equipment comparison.
Compressor Power
Compressor power depends on cooling load and efficiency. EER links delivered cooling to electrical input. Higher EER means the compressor needs fewer watts. The tool also estimates horsepower and running current. These values help compare electrical demand. They are not a replacement for nameplate ratings.
Safety Margin and Oversizing
A small safety margin covers uncertain field conditions. Too much margin can oversize the equipment. Oversized systems may short cycle. They can cool quickly but remove less moisture. Undersized systems may run continuously during hot weather. Balanced sizing gives better comfort and steadier performance.
Best Practical Use
Use this calculator for early design checks, comparisons, and planning. Try several scenarios. Change insulation, windows, sunlight, and air leakage. Watch how the required compressor size changes. For final installation, compare the result with manufacturer tables and a detailed local load calculation.
FAQs
1. What does AC compressor size mean?
It means the cooling capacity and power level needed to remove heat from a room or zone. It is commonly shown in BTU/hr, tons, kilowatts, or horsepower.
2. How many BTU are in one ton of cooling?
One ton of cooling equals 12,000 BTU per hour. Divide the required BTU/hr by 12,000 to estimate the cooling tonnage.
3. Is a larger compressor always better?
No. Oversized compressors can short cycle, waste energy, and reduce moisture removal. Correct sizing usually gives better comfort and equipment life.
4. Why does window area affect compressor size?
Windows can add heat through sunlight and conduction. Large or single-pane windows often increase the cooling load and require more capacity.
5. What is EER in this calculator?
EER means energy efficiency ratio. It compares cooling output in BTU/hr with electrical input in watts. Higher EER reduces estimated compressor power.
6. Why add a safety margin?
A safety margin covers uncertain factors, such as leakage, future appliance loads, or unusual heat gain. Keep it moderate to avoid oversizing.
7. Can this replace a professional load calculation?
No. It is a planning calculator. Final equipment selection should consider building codes, duct design, refrigerant data, orientation, and local conditions.
8. Why does humidity increase the result?
Humid air adds latent cooling load. The system must remove moisture as well as heat, so humid spaces may need extra capacity.