Calculate required room air-conditioner capacity from room dimensions, ceiling height, sun exposure, occupancy, and kitchen use, with results in BTU/h, kW, and refrigeration tons.
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Cooling Capacity Formula
The calculator estimates room-unit cooling capacity or converts an existing capacity. General heat-transfer formulas below provide background; they are not additional calculator modes.
Room AC BTU Formula
- BTU/hr = estimated cooling capacity in British thermal units per hour
- B = base cooling capacity from the room area table
- M_h = retained approximate ceiling factor: height divided by 8 ft, minimum 0.85; not an ENERGY STAR scaling rule
- P_a = people adjustment, equal to 600 BTU/hr for each person above 2 people
- R_a = kitchen allowance of 4,000 BTU/hr when selected
- Insulation is not an input in this simplified guide.
- M_s = sun exposure multiplier
- Climate is not an input in this simplified guide.
- kW = equivalent cooling power in kilowatts
- Tons = refrigeration tons
The Room AC estimate uses the ENERGY STAR area guide for an 8 ft ceiling, applies the disclosed approximate ceiling and sun factors, then adds occupancy and kitchen allowances. Areas must be 100–2,500 sq ft. Insulation, climate and equipment loads require separate assessment.
Detailed load assessment
A general building load calculation also needs envelope, ventilation, humidity and climate data. This simplified room guide does not calculate those loads or prescribe system airflow.
Water Cooling Formula
- Q = cooling capacity in kW
- m_dot = mass flow rate in kg/s
- Cp = specific heat capacity in kJ/kg·K
- DeltaT = absolute temperature difference between inlet and outlet in K or °C
- BTU/hr = heat transfer rate in British thermal units per hour
- Tons = refrigeration tons
For the background water example, convert volume flow to mass flow and multiply by specific heat and temperature difference. The calculator above does not take water-flow or temperature inputs.
Typical Cooling Capacity Reference Values
Use these values as a quick check against the result. Actual sizing can change with insulation, windows, sun exposure, occupancy, and equipment heat.
| Room area | Typical base capacity | Approximate tons |
|---|---|---|
| 100 to 150 sq ft | 5,000 BTU/hr | 0.42 tons |
| 250 to 300 sq ft | 7,000 BTU/hr | 0.58 tons |
| 350 to 400 sq ft | 9,000 BTU/hr | 0.75 tons |
| 450 to 550 sq ft | 12,000 BTU/hr | 1.00 ton |
| 700 to 1,000 sq ft | 18,000 BTU/hr | 1.50 tons |
| 1,000 to 1,200 sq ft | 21,000 BTU/hr | 1.75 tons |
| Conversion | Value | Use |
|---|---|---|
| 1 refrigeration ton | 12,000 BTU/hr | Common air conditioner sizing |
| 1 kW | 3,412.142 BTU/hr | Power and heat transfer conversion |
| Typical AC airflow | System-specific; follow design specifications | Not determined by this calculator |
| Water specific heat | 4.186 kJ/kg·K | Water cooling calculation |
| Water density | About 1000 kg/m³ | Flow-to-mass-flow conversion |
Cooling Capacity Examples
Example 1: Room AC cooling capacity
You have a 400 sq ft room with an 8 ft ceiling, 2 regular occupants, typical sun exposure and standard room use; no separate insulation or climate factors.
The estimated cooling capacity is 9,000 BTU/hr, which is 0.75 tons or about 2.64 kW.
Example 2: Water cooling capacity
You have water flowing at 1 L/s, with an inlet temperature of 20°C and an outlet temperature of 15°C. Use water properties of 4.186 kJ/kg·K and 1000 kg/m³.
The cooling capacity is about 20.93 kW, or about 71,415 BTU/hr.
FAQ
What is cooling capacity?
Cooling capacity is the rate at which a cooling system removes heat. It is commonly shown in BTU/hr, kW, or refrigeration tons. A larger value means the system can remove more heat per hour.
Is a bigger cooling capacity always better?
No. An oversized air conditioner may cool the space too quickly without running long enough to remove humidity well. It can also cycle on and off more often. An undersized unit may run continuously and still not reach the desired temperature. The best size is close to the actual load, with reasonable allowance for sun, insulation, occupancy, and equipment heat.
Why does water cooling use inlet and outlet temperature difference?
Water cooling is based on how much heat the water gains or loses as it flows through the system. The larger the flow rate or temperature difference, the larger the heat transfer. That is why the formula uses mass flow rate, specific heat capacity, and the inlet-to-outlet temperature difference.
