BTU to Watts Converter
Convert BTU/hr to watts and watts to BTU/hr. Used for air conditioning, heating, and appliance energy ratings. Free online converter, instant results.
BTU/hr to Watts Conversion Formula
The British Thermal Unit (BTU) is a traditional unit of heat energy defined as the amount of energy needed to raise the temperature of one pound of water by one degree Fahrenheit. When we talk about BTU per hour (BTU/hr), we are describing a rate of energy transfer—essentially power. The conversion factor to watts is: 1 BTU/hr = 0.293071 watts.
To convert BTU/hr to watts, multiply the BTU value by 0.293071. To convert watts to BTU/hr, divide the watt value by 0.293071 (or equivalently, multiply by 3.41214). These conversion factors are exact, based on the internationally agreed thermochemical definition of the BTU.
The formula is straightforward:
- Watts = BTU/hr × 0.293071
- BTU/hr = Watts × 3.41214
Common conversions you will encounter:
- 5,000 BTU/hr = 1,465 W (small window AC unit)
- 8,000 BTU/hr = 2,344 W (medium window AC unit)
- 10,000 BTU/hr = 2,931 W (large window AC unit)
- 12,000 BTU/hr = 3,517 W (1 ton of cooling)
- 18,000 BTU/hr = 5,275 W (1.5 tons of cooling)
- 24,000 BTU/hr = 7,034 W (2 tons of cooling)
- 36,000 BTU/hr = 10,551 W (3 tons of cooling)
- 60,000 BTU/hr = 17,584 W (5 tons of cooling)
The BTU is used predominantly in the United States, the United Kingdom, and a few other countries for rating heating and cooling equipment. The rest of the world uses watts and kilowatts exclusively. Understanding both units is essential when comparing equipment specifications from different manufacturers or when reading technical documentation from different regions.
What Is a BTU? History and Definition
The British Thermal Unit has a rich history dating back to the early 19th century. It was first introduced around 1845 as a practical unit for measuring heat energy in steam engineering and has remained in widespread use in North America ever since.
Formally, one BTU is defined as the amount of heat required to raise the temperature of one pound (0.4536 kg) of water by one degree Fahrenheit (0.5556 °C) at a constant pressure of one atmosphere. Because the specific heat of water varies slightly with temperature, several different definitions of the BTU exist:
- Thermochemical BTU: 1,054.350 joules (the most commonly used definition)
- International Table BTU: 1,055.056 joules
- Mean BTU: 1,055.87 joules (averaged over 0–100 °C)
- 39 °F BTU: 1,059.67 joules (at the temperature where water is densest)
For practical purposes in HVAC and appliance ratings, these differences are negligible. The International Table BTU (1,055.056 J) is the most commonly referenced in modern engineering standards. One BTU/hr equals approximately 0.293071 watts, which is the conversion factor used in this calculator.
In contrast, the watt is the SI (International System of Units) unit of power, defined as one joule per second. Named after James Watt, it is used universally in science and engineering and is the standard unit for electrical power ratings worldwide. While the BTU is gradually being phased out in some contexts, it remains deeply entrenched in the North American HVAC industry.
Air Conditioner BTU Ratings and Room Sizing
Air conditioners in the United States are almost universally rated in BTU/hr. Selecting the right BTU rating for your space is critical—too small and the unit will run continuously without adequately cooling the room, too large and it will short-cycle (turning on and off frequently), which wastes energy, increases wear on the compressor, and fails to dehumidify the air properly.
The general guideline from the U.S. Department of Energy for room air conditioners is approximately 20 BTU per square foot of living space, but this varies based on several factors:
| Room Size (sq ft) | Recommended BTU/hr | Equivalent Watts | Equivalent kW |
|---|---|---|---|
| 100–150 | 5,000 | 1,465 | 1.47 |
| 150–250 | 6,000 | 1,758 | 1.76 |
| 250–300 | 7,000 | 2,051 | 2.05 |
| 300–350 | 8,000 | 2,344 | 2.34 |
| 350–400 | 9,000 | 2,638 | 2.64 |
| 400–450 | 10,000 | 2,931 | 2.93 |
| 450–550 | 12,000 | 3,517 | 3.52 |
| 550–700 | 14,000 | 4,103 | 4.10 |
| 700–1,000 | 18,000 | 5,275 | 5.28 |
| 1,000–1,200 | 21,000 | 6,154 | 6.15 |
| 1,200–1,400 | 23,000 | 6,741 | 6.74 |
| 1,400–1,500 | 24,000 | 7,034 | 7.03 |
Additional adjustments to consider:
- If the room gets heavy sun exposure, add 10 percent to the BTU requirement.
- If the room is heavily shaded, reduce by 10 percent.
- If more than two people regularly occupy the room, add 600 BTU per additional person.
- If the unit is for a kitchen, add 4,000 BTU to account for heat from cooking appliances.
- For rooms with high ceilings (above 8 feet), increase BTU by roughly 20–25 percent.
The term "1 ton of cooling" equals 12,000 BTU/hr, which equals 3,517 watts or 3.52 kW. This unit originated from the era of ice-based cooling, where one ton referred to the cooling power provided by melting one short ton (2,000 pounds) of ice over a 24-hour period.
Heating Systems and BTU Ratings
Furnaces, boilers, water heaters, and other heating appliances are also rated in BTU/hr in North America. Understanding these ratings helps homeowners compare systems, estimate fuel costs, and ensure their heating equipment is properly sized for their home.
Typical BTU ratings for common heating systems:
- Gas furnace (residential): 40,000–120,000 BTU/hr (11.7–35.2 kW)
- Gas boiler (residential): 50,000–200,000 BTU/hr (14.7–58.6 kW)
- Tank water heater (40 gal): 30,000–40,000 BTU/hr (8.8–11.7 kW)
- Tankless water heater: 150,000–200,000 BTU/hr (44.0–58.6 kW)
- Gas fireplace insert: 20,000–40,000 BTU/hr (5.9–11.7 kW)
- Pellet stove: 8,000–90,000 BTU/hr (2.3–26.4 kW)
- Portable propane heater: 4,000–18,000 BTU/hr (1.2–5.3 kW)
An important concept with heating systems is efficiency rating. A furnace rated at 100,000 BTU/hr input with 96 percent AFUE (Annual Fuel Utilization Efficiency) delivers 96,000 BTU/hr of actual heat to your home. The remaining 4 percent is lost through exhaust gases. When comparing heating systems, always consider the output BTU rating (or convert to watts) after accounting for efficiency.
To estimate your home's heating requirement, a simplified rule of thumb is 25–30 BTU per square foot in cold climates (Northern US, Canada) and 15–20 BTU per square foot in mild climates (Southern US). A 2,000-square-foot home in Minnesota might need 50,000–60,000 BTU/hr (14.7–17.6 kW), while the same home in Georgia might need 30,000–40,000 BTU/hr (8.8–11.7 kW). A proper Manual J load calculation performed by an HVAC professional provides a much more accurate estimate.
Energy Efficiency: EER, SEER, and COP
When shopping for air conditioners and heat pumps, you will encounter various efficiency metrics. Understanding how these relate to BTU and watts helps you make informed purchasing decisions and estimate operating costs.
EER (Energy Efficiency Ratio): Defined as the cooling capacity in BTU/hr divided by the power input in watts, measured at a specific outdoor temperature (typically 95°F). An air conditioner with a 12,000 BTU/hr capacity that consumes 1,200 watts has an EER of 10. Higher EER values indicate better efficiency.
SEER (Seasonal Energy Efficiency Ratio): Similar to EER but averaged over an entire cooling season with varying outdoor temperatures. SEER values are typically higher than EER values for the same equipment. Modern split-system air conditioners in the US must have a minimum SEER of 14 (15 in southern states as of 2023). High-efficiency models achieve SEER 20–25 or higher.
COP (Coefficient of Performance): Used for heat pumps. COP equals the heating or cooling output in watts divided by the electrical input in watts. A COP of 3.0 means the system delivers 3 watts of heating for every 1 watt of electricity consumed. To convert EER to COP, divide by 3.412: EER 12 ÷ 3.412 = COP 3.52.
HSPF (Heating Seasonal Performance Factor): The heating equivalent of SEER for heat pumps. Defined as total heating output in BTU over a heating season divided by total electrical input in watt-hours. Minimum HSPF for new equipment in the US is 8.8. High-efficiency heat pumps achieve HSPF 10–13.
To estimate annual electricity cost for an air conditioner: divide the BTU capacity by the SEER rating to get average watts consumed, multiply by estimated cooling hours per year, divide by 1,000, and multiply by your electricity rate. For example, a 24,000 BTU/hr unit with SEER 16 consumes an average of 1,500 watts. Over 1,000 cooling hours per year at $0.13/kWh, that equals $195 per year in electricity.
BTU to Watts Conversion Reference Table
Use this comprehensive reference table for quick BTU/hr to watts conversions. The table covers common values encountered in HVAC, heating, water heating, and industrial applications. Remember: 1 BTU/hr = 0.293071 W.
| BTU/hr | Watts | Kilowatts | Typical Application |
|---|---|---|---|
| 1,000 | 293 | 0.29 | Small space heater (low) |
| 3,000 | 879 | 0.88 | Portable radiator (low) |
| 5,000 | 1,465 | 1.47 | Small window AC |
| 6,000 | 1,758 | 1.76 | Medium window AC |
| 8,000 | 2,344 | 2.34 | Large window AC |
| 10,000 | 2,931 | 2.93 | Large window AC |
| 12,000 | 3,517 | 3.52 | 1 ton / mini-split |
| 18,000 | 5,275 | 5.28 | 1.5 ton mini-split |
| 24,000 | 7,034 | 7.03 | 2 ton split system |
| 30,000 | 8,792 | 8.79 | 2.5 ton split system |
| 36,000 | 10,551 | 10.55 | 3 ton central AC |
| 48,000 | 14,067 | 14.07 | 4 ton central AC |
| 60,000 | 17,584 | 17.58 | 5 ton central AC / furnace |
| 80,000 | 23,446 | 23.45 | Residential furnace |
| 100,000 | 29,307 | 29.31 | Large furnace |
| 150,000 | 43,961 | 43.96 | Tankless water heater |
| 200,000 | 58,614 | 58.61 | Commercial boiler |
| 400,000 | 117,228 | 117.23 | Light commercial HVAC |
How to Use This BTU to Watts Calculator
This free online converter makes it easy to switch between BTU/hr and watts. It works in both directions simultaneously, so you can enter either value and see the conversion instantly.
- Enter BTU/hr: Type the BTU per hour rating from your appliance specification sheet, product listing, or owner's manual into the BTU/hr field.
- Enter Watts: Alternatively, enter a wattage value if you want to know the equivalent in BTU/hr.
- Read both results: The calculator instantly displays both conversions—BTU/hr to watts and watts to BTU/hr—so you always get the information you need.
Example 1: You are shopping for a window air conditioner rated at 8,000 BTU/hr and want to know the electrical load. Enter 8,000 in the BTU/hr field. Result: 2,344 watts. This tells you the unit's cooling capacity in metric terms, but note that the actual electrical consumption will be lower, depending on the unit's EER rating.
Example 2: You have a 1,500-watt portable electric heater and want to know its heat output in BTU/hr. Enter 1,500 in the Watts field. Result: 5,118 BTU/hr. Since electric heaters convert nearly 100 percent of electricity to heat, this is the actual heat delivered to the room.
Example 3: A furnace is rated at 80,000 BTU/hr input. Enter 80,000 in the BTU/hr field to see 23,446 watts (23.4 kW). If the furnace has 95 percent efficiency, the actual heat output is 76,000 BTU/hr (22,273 W).
Frequently Asked Questions
How many watts is 12,000 BTU?
12,000 BTU/hr × 0.293071 = 3,517 watts (3.52 kW). This is equivalent to 1 ton of cooling capacity, the standard unit used in the HVAC industry. A 12,000 BTU/hr air conditioner's actual electrical consumption will be lower than 3,517 watts because the EER or SEER rating indicates how efficiently it converts electricity into cooling.
How do I convert BTU to watts?
Multiply BTU/hr by 0.293071. For example, 5,000 BTU/hr × 0.293071 = 1,465.4 watts. For a quick mental estimate, divide BTU/hr by 3.4 to get an approximate wattage.
What does 1 ton of cooling mean in watts?
One ton of cooling equals 12,000 BTU/hr, which equals 3,516.9 watts (3.52 kW). The term originates from the amount of cooling provided by melting one short ton (2,000 pounds) of ice over 24 hours. Residential central air conditioners typically range from 1.5 to 5 tons (18,000–60,000 BTU/hr or 5.3–17.6 kW).
How do I convert watts to BTU/hr?
Multiply watts by 3.41214. For example, 2,000 watts × 3.41214 = 6,824 BTU/hr. This is useful when comparing electric heaters (rated in watts) to gas heaters (rated in BTU/hr).
What size air conditioner do I need for a 500-square-foot room?
For a 500-square-foot room, you generally need approximately 10,000–12,000 BTU/hr (2,931–3,517 watts). Adjust upward for sunny exposure, high ceilings, or hot climates, and downward for shaded rooms or mild climates. A Manual J calculation provides the most accurate sizing.
Are BTU and BTU/hr the same thing?
No. BTU is a unit of energy (like joules), while BTU/hr is a unit of power (like watts). When HVAC manufacturers list a product as "12,000 BTU," they almost always mean 12,000 BTU/hr—the rate of energy transfer. One BTU of energy equals 1,055 joules or 0.000293 kilowatt-hours.
Why do American appliances use BTU instead of watts?
The BTU has been used in American engineering since the mid-1800s and became deeply embedded in the HVAC, plumbing, and natural gas industries. While the scientific and electrical communities use watts, the HVAC industry in North America has continued with BTU/hr by tradition. Equipment sold internationally typically lists both BTU/hr and watts or kilowatts.
How many BTU does a 1,500-watt heater produce?
1,500 watts × 3.41214 = 5,118 BTU/hr. Electric heaters are nearly 100 percent efficient at converting electricity to heat (all the electricity becomes heat in the room), so the electrical input and heat output are essentially the same.
What is the difference between EER and SEER?
EER (Energy Efficiency Ratio) measures efficiency at a single test condition (typically 95°F outdoor temperature). SEER (Seasonal Energy Efficiency Ratio) averages efficiency over an entire cooling season with varying temperatures. SEER values are usually higher than EER for the same equipment. Both are expressed as BTU/hr per watt.
How do I calculate the running cost of an air conditioner in BTU?
Divide the BTU/hr rating by the EER to get watts consumed. Multiply watts by hours of use, divide by 1,000 to get kWh, and multiply by your electricity rate. Example: A 12,000 BTU/hr unit with EER 12 uses 1,000 watts. Running 8 hours a day at $0.15/kWh costs $1.20 per day or about $36 per month.