How to Convert BTU per Hour to Watts
Converting BTU per hour to watts is an essential calculation in heating, ventilation, and air conditioning (HVAC), energy engineering, and building science. The BTU per hour (BTU/h) is a unit of power used primarily in the United States to rate the heating and cooling capacity of HVAC equipment, furnaces, water heaters, and other thermal systems. The watt (W) is the SI unit of power used internationally for all forms of energy transfer. One BTU per hour equals approximately 0.293071 watts. This conversion is critical for HVAC engineers designing systems for international markets, for building scientists comparing energy performance data across different standards, and for manufacturers exporting heating and cooling equipment from the US to metric-system countries. As global energy efficiency standards increasingly use watts and kilowatts, the ability to convert from BTU/h to watts has become a practical necessity for anyone involved in building energy management, equipment specification, or international trade in thermal systems. Understanding this conversion helps professionals communicate effectively across the American and international engineering communities.
Conversion Formula
To convert BTU per hour to watts, multiply the power in BTU/h by 0.293071. This factor is derived from the definition of the British Thermal Unit: one BTU is the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit, which equals approximately 1,055.06 joules. Since one watt equals one joule per second and there are 3,600 seconds in an hour, dividing 1,055.06 by 3,600 gives approximately 0.293071 watts per BTU/h.
Watts = BTU/h × 0.293071
5 btu per hour = 1.46535 watts
Step-by-Step Example
To convert 5 BTU/h to watts:
1. Start with the value: 5 BTU/h
2. Multiply by the conversion factor: 5 × 0.293071
3. Calculate: 5 × 0.293071 = 1.46535
4. Result: 5 BTU/h = 1.46535 watts
Five BTU/h is a very small amount of power. A more practical example: a window air conditioner rated at 12,000 BTU/h equals approximately 3,517 watts or 3.52 kilowatts.
Understanding BTU per Hour and Watts
What is a BTU per Hour?
The British Thermal Unit (BTU) was developed in the early 19th century as scientists sought to quantify heat energy. It was defined as the amount of heat needed to raise the temperature of one pound of water by one degree Fahrenheit. The "per hour" addition created a power unit (BTU/h) for measuring rates of heat transfer. The BTU became the standard unit for the American heating and cooling industry, which grew rapidly in the 20th century with the widespread adoption of central heating and air conditioning. Despite its name, the BTU is no longer commonly used in Britain, which has largely adopted SI units. In the United States, the BTU/h remains the primary unit for rating HVAC equipment, gas appliances, and heating fuel energy content.
What is a Watt?
The watt, named after James Watt, was adopted as the SI unit of power in 1882 and is defined as one joule per second. While originally associated primarily with mechanical and electrical power, the watt is equally valid for measuring thermal power (the rate of heat transfer). International energy standards, including those from the International Energy Agency and the European Union, use watts and kilowatts for thermal system ratings. The global trend toward using watts in HVAC and building energy performance has accelerated with international energy efficiency standards and the growing importance of building energy modeling, which standardizes on SI units for global comparability.
Practical Applications
BTU/h-to-watt conversion is used daily by HVAC engineers designing systems for buildings with international specifications. Air conditioning units sold in the US are rated in BTU/h (commonly 5,000 to 60,000 BTU/h for residential units), but must be converted to watts for markets using SI units. Building energy modeling software may require inputs in watts or kilowatts while equipment specifications are in BTU/h. Furnace and boiler manufacturers convert output ratings for export markets. Energy auditors convert between units when comparing heating system performance across different standards. Industrial process heating systems rated in BTU/h require watt conversions for electrical system planning and international reporting.
Tips and Common Mistakes
A critical mistake is confusing BTU (a unit of energy) with BTU per hour (a unit of power). BTU alone measures heat energy, while BTU/h measures the rate of heat transfer, which is power. Another common error is using the wrong BTU definition: the International Table BTU (1,055.06 J) is the most common, but the thermochemical BTU (1,054.35 J) and the 59 degree Fahrenheit BTU (1,054.80 J) also exist, each giving slightly different conversion factors. For HVAC purposes, the IT BTU is standard. When converting large values, divide by 3,412 to get kilowatts directly (since 1 kW = 3,412 BTU/h). Also, remember that HVAC efficiency ratings (like SEER or EER) involve BTU/h per watt of electrical input, so do not confuse rated capacity with electrical consumption.
Frequently Asked Questions
Twelve thousand BTU/h equals approximately 3,517 watts or about 3.52 kilowatts. This is the standard rating for a "1-ton" air conditioning unit, one of the most common residential cooling capacities. The calculation is 12,000 × 0.293071 = 3,516.85 watts.