Cooling Load Results
Detailed estimateLoad breakdown
Sizing notes and warnings
Step-by-step calculation
Formula Used
Base load: Floor area × base BTU factor × ceiling-height factor.
Adjusted envelope load: Base load × climate × insulation × sun × orientation × floor × exterior-wall × wall × roof factors.
Internal load: Occupants + lighting watts × 3.412 + equipment watts × 3.412 × diversity factor + kitchen load.
Ventilation load: 1.08 × CFM × temperature difference, plus a humidity allowance.
Final load: Subtotal × air-leakage factor × (1 + duct loss) × (1 + safety margin).
Cooling tons: Final BTU/h ÷ 12,000.
How to Use This Calculator
- Select quick, detailed, or multi-room calculation mode.
- Choose imperial or metric measurements before entering dimensions.
- Enter room size, exposure, windows, occupants, and internal heat sources.
- Add ventilation, duct loss, humidity, and a reasonable design margin.
- Enter efficiency, operating schedule, and electricity rate for cost estimates.
- Select Calculate AC tonnage and review warnings before choosing equipment.
AC Tonnage and BTU Reference
| Nominal size | Cooling capacity | Approximate cooling kW | Typical planning range |
|---|---|---|---|
| 0.75 ton | 9,000 BTU/h | 2.64 kW | Small bedroom or office |
| 1 ton | 12,000 BTU/h | 3.52 kW | Small room or compact zone |
| 1.5 tons | 18,000 BTU/h | 5.28 kW | Medium room or apartment zone |
| 2 tons | 24,000 BTU/h | 7.03 kW | Large room or small residence |
| 3 tons | 36,000 BTU/h | 10.55 kW | Medium residence or commercial zone |
| 5 tons | 60,000 BTU/h | 17.58 kW | Large residence or light commercial area |
Worked Example
| Input | Example value | Effect |
|---|---|---|
| Room size | 25 × 20 × 9 feet | Sets area and ceiling volume factor |
| Climate | Hot | Raises the envelope load |
| Windows | 60 ft², double-pane | Adds solar and conductive gain |
| Occupants | 4 people | Adds sensible and latent heat |
| Equipment | 800 watts | Adds internal heat |
| Design margin | 10% | Provides a limited planning reserve |
Understanding Air Conditioning Tonnage
Air conditioning tonnage describes cooling capacity, not equipment weight. One refrigeration ton equals twelve thousand BTU each hour. Correct capacity improves comfort, humidity control, and system reliability.
Floor area provides only a starting estimate for cooling. Ceiling height, sunlight, insulation, and windows change heat gain. Detailed inputs produce a more useful planning estimate overall.
People, lighting, computers, cooking, and machinery release indoor heat. Busy spaces therefore need more cooling than empty rooms. Diversity factors prevent every appliance being counted at maximum.
Fresh outdoor air also creates sensible and latent loads. Hot humid air can greatly increase moisture removal demand. Humid climates often require lower airflow for dehumidification control.
Ducts located outside conditioned space may lose useful cooling. Leaky returns can also pull hot air indoors. Good duct sealing protects capacity and reduces energy waste.
An oversized unit may cool quickly but cycle frequently. Short cycling can reduce comfort and humidity removal. Undersized equipment may run continuously during peak weather conditions.
Efficiency ratings estimate how much electricity cooling equipment consumes. Higher SEER2, SEER, EER, or COP values reduce usage. Actual bills still depend on runtime and local weather.
A safety margin should remain modest and technically justified. Excessive margins often produce oversized, inefficient equipment selections. Professional load calculations remain best for final design decisions.
Frequently Asked Questions
What does one ton of AC mean?
One ton of air conditioning equals 12,000 BTU of cooling per hour.
Can floor area alone determine tonnage?
No. Area offers a rough estimate, while climate, windows, insulation, people, and equipment can substantially change the required capacity.
Should I round up to the next standard size?
Usually the calculated load is compared with nearby standard sizes. Avoid automatically selecting a much larger unit without professional review.
Why does humidity matter?
Cooling systems must remove both temperature heat and moisture. Humid outdoor air increases the latent cooling requirement.
How much airflow does each ton need?
A common planning value is about 400 CFM per ton. Humid applications may use lower airflow under proper design controls.
What is duct loss?
Duct loss represents cooling lost through leakage, conduction, and poorly conditioned duct locations.
Does a higher SEER2 rating reduce tonnage?
No. Efficiency changes energy consumption, while tonnage describes the cooling capacity needed for the load.
Can this calculator size commercial systems?
It can provide a planning estimate for simple zones. Complex commercial projects need professional engineering and recognized load-calculation methods.
Is this a replacement for Manual J or engineered design?
No. Use the result for preliminary planning, then verify final equipment through an accepted professional calculation.