Heat Rate Converter
Convert heat rate and thermal power between watts, BTU/h, calories per second, tons of refrigeration, and boiler horsepower with instant results.
Heat Rate Converter
Calculator
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Formula: Converted Value = Input Value x (From Unit Factor / To Unit Factor)
Worked example — 36,000 BTU/h = 10.55 kW = 3.0 TR
Formula
Converted Value = Input Value x (From Unit Factor / To Unit Factor)
Heat rate conversion uses watts as the base unit. Each unit has a known factor relative to watts. For instance, 1 BTU/h = 0.29307 W and 1 ton of refrigeration = 3,516.853 W. To convert, multiply the input by its factor to get watts, then divide by the target unit factor to get the result.
Worked Examples
Example 1: HVAC System Conversion
Problem:An air conditioning unit is rated at 36,000 BTU/h. Convert to kilowatts and tons of refrigeration.
Solution:To kW: 36,000 BTU/h x 0.29307107 W per BTU/h = 10,550.6 W = 10.55 kW To TR: 36,000 / 12,000 = 3.0 tons of refrigeration
Result:36,000 BTU/h = 10.55 kW = 3.0 TR
Example 2: Boiler Rating Conversion
Problem:A steam boiler is rated at 5 boiler horsepower. What is this in kW and BTU/h?
Solution:To watts: 5 x 9,809.5 = 49,047.5 W = 49.05 kW To BTU/h: 49,047.5 / 0.29307107 = 167,375 BTU/h Alternatively: 5 x 33,475 = 167,375 BTU/h
Result:5 boiler HP = 49.05 kW = 167,375 BTU/h
Frequently Asked Questions
What is heat rate and how is it measured?
Heat rate is the rate of thermal energy transfer per unit of time. It is essentially thermal power and is measured in watts (W) in the SI system. In HVAC and power generation, BTU per hour is commonly used. Heat rate in power plants specifically refers to the amount of fuel energy required to generate one kilowatt-hour of electricity, typically expressed as BTU/kWh. Lower heat rates indicate higher efficiency.
How do you convert BTU/h to watts?
To convert BTU per hour to watts, multiply the BTU/h value by 0.29307107. This conversion factor comes from the definition that 1 BTU equals 1,055.0559 joules and 1 hour equals 3,600 seconds. So 1 BTU/h = 1,055.0559 J / 3,600 s = 0.29307 W. For quick mental math, roughly 3.412 BTU/h equals 1 watt.
What is a ton of refrigeration?
A ton of refrigeration (TR) is a unit of heat rate used in HVAC and refrigeration industries. It equals the rate of heat transfer needed to melt one short ton (2,000 pounds) of ice at 0 degrees C in 24 hours. Numerically, 1 TR = 12,000 BTU/h = 3,516.853 watts = 3.517 kW. This unit originated in the ice harvesting industry and remains the standard for rating air conditioning system capacity in North America.
What is boiler horsepower?
Boiler horsepower is a unit of heat rate used to measure the output of steam boilers. One boiler horsepower equals 33,475 BTU/h or approximately 9,809.5 watts. It was originally defined as the power needed to evaporate 34.5 pounds of water per hour at 212 degrees F. Despite its name, boiler horsepower is roughly 13.15 times larger than mechanical horsepower. Modern usage has declined in favor of BTU/h or kW ratings.
What is the difference between power-plant heat rate and HVAC thermal power?
They share a name but not a dimension. HVAC thermal power is energy per unit time, expressed in watts or BTU/h, and describes how fast heat moves. Power-plant heat rate is fuel energy input per unit of electrical energy output, expressed in BTU/kWh or kJ/kWh, and the time units cancel out. This converter handles the first kind, the thermal power form. Feeding a BTU/kWh figure through a BTU/h factor is a dimensional error and produces a meaningless number.
How do you turn a plant heat rate in BTU/kWh into thermal efficiency?
One kilowatt-hour of electricity equals 3,412.14 BTU of energy, so efficiency is that constant divided by the heat rate. A unit with a heat rate of 10,000 BTU/kWh converts 3,412.14 / 10,000 = 34.1 percent of its fuel energy into electricity. A combined-cycle plant near 6,800 BTU/kWh reaches roughly 50 percent. Because the constant is fixed, a lower heat rate always means higher efficiency, and the two quantities are simple reciprocals of each other scaled by 3,412.14.
What does MBH mean on an HVAC equipment nameplate?
MBH means thousands of BTU per hour, where the leading M is the Roman numeral for one thousand rather than the metric mega prefix. One MBH therefore equals 1,000 BTU/h, which is 293.07 watts or 0.29307 kW. The notation survives on boiler, furnace and coil nameplates in North America. The ambiguity is a real hazard: reading MBH as megaBTU/h overstates capacity by a factor of a thousand, so confirm from the equipment class whether a rating of 400 means 400,000 BTU/h.
How many kilowatts of cooling is one ton of refrigeration?
One ton of refrigeration equals 12,000 BTU/h, which converts to 3,516.85 watts, about 3.517 kW of heat removal. Running it the other way, 1 kW of cooling is 1,000 / 3,516.85 = 0.2843 tons. Note that this is cooling capacity, not electrical input: a chiller rated at 100 tons removes about 352 kW of heat while drawing considerably less electrical power, and the ratio between the two is what coefficient of performance and energy efficiency ratio describe.
What is the relationship between calories per second and kilocalories per hour?
One calorie per second equals 4.1868 watts and one kilocalorie per hour equals 1.163 watts, so dividing gives 4.1868 / 1.163 = 3.6. One cal/s is therefore exactly 3.6 kcal/h. The factor follows directly from multiplying by 3,600 seconds per hour and dividing by 1,000 calories per kilocalorie. Kilocalories per hour appear in older European heating literature and in food science, while calories per second show up in laboratory calorimetry.
Why is the same watt used for both thermal and electrical power?
The watt is defined purely as one joule per second, with no reference to the form the energy takes. Because the first law of thermodynamics treats heat and work as interchangeable expressions of energy, a resistive heater drawing 1,500 electrical watts dissipates 1,500 thermal watts. That equivalence is why electric resistance heating is effectively 100 percent efficient at the appliance, and why a cooling load calculation can add lighting watts, equipment watts and solar gain into a single figure in BTU/h.
References
Reviewed for accuracy by Manoj Kumar, Mathematics Educator · Editorial policy
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