🌡️ HVAC
HVAC & Thermal Energy
Convert heating and cooling energy, power and airflow. Choose a category, enter a value, then press Convert.
About the HVAC & Thermal Energy
HVAC calculations mix three different dimensions. Energy is measured in BTU, kWh, therms or joules; power in BTU/h, kW, tons of refrigeration or horsepower; airflow in CFM or m³/h. Converting between energy and power requires a time, so this converter keeps them in separate categories.
One ton of refrigeration is 12,000 BTU/h, about 3.517 kW — the heat absorbed by melting a ton of ice per day. A therm is 100,000 BTU, and 1 kWh is 3,412 BTU. Airflow conversion is simpler: 1 CFM is 1.699 m³/h, and 1 m³/h is 0.5886 CFM.
How the calculation works
- 1 kWh = 3,412.14 BTU = 0.0341214 therms.
- 1 ton of refrigeration = 12,000 BTU/h = 3.51685 kW.
- 1 horsepower = 0.7457 kW = 2,544.4 BTU/h.
- 1 CFM = 1.69901 m³/h = 0.471947 L/s.
Reference values
| HVAC quantity | Value | Equivalent |
|---|---|---|
| 1 ton cooling | 12,000 BTU/h | 3.517 kW |
| 1 kW | 3,412 BTU/h | 0.284 ton |
| 1 therm | 100,000 BTU | 29.31 kWh |
| 1 hp | 2,544 BTU/h | 0.746 kW |
| 1 CFM | 1.699 m³/h | 0.472 L/s |
| 1 m³/h | 0.5886 CFM | 0.2778 L/s |
Worked example: sizing a room unit
A 3-ton air conditioner is 36,000 BTU/h, or 10.55 kW. A 2 kW electric heater delivers 6,824 BTU/h, and a 1,500 W space heater delivers 5,118 BTU/h—about 0.43 ton of heating. A 1,000 CFM air handler moves 1,699 m³/h, which is 0.472 m³/s.
Keep energy and power separate when checking a quotation. A 3-ton unit is a power rating (12,000 BTU/h per ton); the energy it uses over an hour depends on how long it runs and its efficiency. A unit with a higher seasonal efficiency can use less electricity for the same cooling output.
Sizing by climate, insulation and room use
A rough sizing rule for cooling is 20 BTU/h per square foot in a well-insulated home, rising to 30 or more in a hot climate or a poorly insulated room. A 400 sq ft living room therefore needs roughly 8,000–12,000 BTU/h, or 0.67–1 ton. That is a starting point for a quote, not a substitute for a room-by-room heat-loss calculation.
Occupancy, glazing, ceiling height and appliances all shift the figure. A kitchen with an oven and a west-facing window can need as much again as a bedroom of the same size. Oversizing is not harmless: a unit that short-cycles cools the air without removing enough moisture, leaving the room cold and clammy.