HVAC Unit Converter
Instant, standards-based conversions for HVAC design, commissioning and site work.
Cooling capacity
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HVAC Unit Conversion Reference
Most conversion errors in HVAC are not arithmetic. They come from mixing up a quantity with a rate, or a cooling output with an electrical input. The three below account for the majority of them.
What is a refrigeration ton?
A refrigeration ton is a unit of cooling capacity, not equipment weight. The name comes from the rate of heat absorption of a ton of ice melting over 24 hours. One TR equals 12,000 International Table BTU per hour.
1 TR = 12,000 BTU/h = 3.51685 kWTR and kW
Both describe the rate at which heat is removed. Multiply TR by 3.51685 to get cooling capacity in kW. This is not the electrical power the unit draws, which is a much smaller number.
Cooling kW = TR × 3.51685BTU and watts
A BTU is an amount of energy. BTU/h is a rate of heat transfer. Equipment capacity should always be written as BTU/h, and a bare "BTU" on a nameplate almost always means BTU/h.
1 W = 3.41214 BTU/hCommon HVAC Unit Conversions
| Quantity | Conversion | Where it comes up |
|---|---|---|
| Cooling capacity | 1 TR = 3.51685 kW | Chillers, DX units, load schedules |
| Cooling capacity | 12,000 BTU/h = 1 TR | Residential and commercial AC ratings |
| Airflow | 1 CFM = 0.471947 L/s | Diffusers, fans, ventilation rates |
| Airflow | 1 CFM = 1.69901 m³/h | AHU and duct schedules |
| Pressure | 1 Pa = 0.101972 mmWC | Duct static pressure, filter drop |
| Velocity | 1 m/s = 196.850 FPM | Duct and grille air velocity |
| Area | 1 m² = 10.7639 ft² | Room and envelope calculations |
Two definitions of the BTU are in circulation. The International Table BTU is the one used throughout HVAC, and it is what the figures above assume. The thermochemical BTU is about 0.07 percent smaller, which is immaterial on a single unit but can produce a visible discrepancy when you are reconciling a large schedule against a manufacturer's total.
Frequently Asked Questions
How do I convert TR to kW?
Multiply refrigeration tons by 3.51685. For example, 5 TR is approximately 17.5843 kW of cooling capacity.
How do I convert BTU/h to kW?
Multiply BTU/h by 0.000293071. For example, 24,000 BTU/h is approximately 7.0337 kW.
What is the difference between cooling kW and electrical kW?
Cooling kW is the rate of heat removed from the space. Electrical kW is the power the unit draws to do it. The ratio between them is the coefficient of performance. A 5 TR unit delivering about 17.58 kW of cooling at a COP of 3.0 draws roughly 5.86 kW electrically. Confusing the two is the most expensive conversion mistake in HVAC, because it leads to cable and breaker sizing that is wrong by a factor of three or more.
How do I convert CFM to L/s?
Multiply CFM by 0.471947. For example, 1,000 CFM is approximately 471.947 L/s.
How do I convert CFM to m³/h?
Multiply CFM by 1.69901. For example, 500 CFM is approximately 849.505 m³/h.
How do I convert Pa to mmWC?
Divide pascals by 9.80665. So 100 Pa is approximately 10.1972 mmWC using the conventional water-column definition.
Which horsepower definition is used?
Mechanical horsepower, where 1 HP equals approximately 745.700 W. Metric horsepower is a different unit at about 735.499 W and is not treated as HP here. Equipment from European manufacturers sometimes quotes the metric figure, so check which one a datasheet means before converting.
Why does my conversion differ slightly from the manufacturer's figure?
Usually rounding, or a different BTU definition. Many datasheets round 3.51685 to 3.5 or 3.517, which shifts a large total by a noticeable amount. Some use the thermochemical BTU rather than the International Table BTU. Neither is wrong, but mixing them within one schedule produces totals that do not reconcile.
Engineering References
Conversion factors here follow the definitions published by NIST and BIPM.
- NIST SP 811, Appendix B — Conversion Factors
- NIST Appendix B.8 — Alphabetical Unit Factors
- BIPM — The International System of Units (SI)
Where These Units Come From
Converting a figure is usually one step inside a larger calculation. These tools produce the numbers you are most likely to be converting.
