HVAC Unit Converter Widget

How it works

Each unit is held as its exact size in watts and a conversion multiplies by the source size and divides by the target size, so no rounded intermediate creeps in. The factors are the NIST SP 811 ones: one international-table BTU per hour is 0.2930711 W, so 1 kW is 3,412.142 BTU/h; a ton of refrigeration is defined as 12,000 BTU/h, or 3.516853 kW; MBH is a thousand BTU/h. Kilocalories per hour use the international-table calorie of 4.1868 J, which makes 1 kcal/h exactly 1.163 W - the convention of European and Asian chiller catalogues. Mechanical horsepower (550 ft.lbf/s) is 745.6999 W and boiler horsepower, still used for steam and hot-water boilers, is 9,809.5 W. The answer is shown with sensible precision, alongside BTU/h, tons, kW and kcal/h for the same figure.

Method

• result = value x size(from) / size(to), with every size in watts
• 1 BTU_IT/h = 1055.05585262 J / 3600 s = 0.2930711 W; 1 kW = 3,412.142 BTU/h
• 1 ton of refrigeration (TR) = 12,000 BTU/h = 3,516.853 W; 1 MBH = 1,000 BTU/h
• 1 kcal_IT/h = 4,186.8 J / 3600 s = 1.163 W
• 1 hp (550 ft.lbf/s) = 745.6999 W; 1 boiler horsepower = 9,809.50 W

Worked examples

Limitations

• Converts capacity (a heat rate) only; it does not convert efficiency ratings such as EER, SEER, COP or kW per ton.
• Nameplate capacities are measured at standard rating conditions; real output changes with outdoor temperature and humidity.
• Refrigeration tons are the US/IT definition (12,000 BTU/h); the rarely used metric or Japanese refrigeration tons are not included.

Where publishers use it

• Split-system and mini-split product pages that list capacity in BTU/h for one market and kW for another
• Chiller and cooling-tower quotes where an engineer needs tons of refrigeration next to kW
• Boiler retrofit articles translating boiler horsepower and MBH ratings into kW
• HVAC apprentice and refrigeration-course pages that drill the 12,000 BTU/h ton
• Import listings of Asian air conditioners rated in kcal/h

Questions

Sources

1. NIST Guide to the SI, Appendix B.8: Factors for Units Listed Alphabetically (SP 811) - National Institute of Standards and Technology . Btu_IT per hour = 2.930711 E-01 W; ton of refrigeration (12 000 Btu_IT/h) = 3.516853 E+03 W; horsepower (550 ft.lbf/s) = 7.456999 E+02 W; horsepower (boiler) = 9.80950 E+03 W; kilocalorie_IT = 4.1868 E+03 J. Checked 2026-10-01.
2. NIST Guide to the SI, Appendix B.9: Factors for units listed by kind of quantity - National Institute of Standards and Technology . The POWER section groups the same four power factors. NIST has no kcal per hour row; 1 kcal_IT/h = 4186.8 J / 3600 s = 1.163 W is derived from the kilocalorie_IT.

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