Loading Calculator...
Please wait a moment
Please wait a moment
Convert British Thermal Units to joules instantly. Free energy converter for HVAC ratings, heating capacity, cooling systems, and thermodynamics with conversion formulas and reference tables.
1055.06 J
per BTU
12,000 BTU/h
= 1 Ton AC
~0.293 W
per BTU/h
Common in HVAC systems
SI unit of energy
1 BTU = 1055.06 joules
Joules = BTU × 1055.06
BTU = Joules ÷ 1055.06
Or: 1 BTU ≈ 1.055 kJ (kilojoules)
| BTU | Joules (J) | Kilojoules (kJ) | Typical Use |
|---|---|---|---|
| 1 BTU | 1,055.06 J | 1.06 kJ | Small heat source |
| 5 BTU | 5,275.3 J | 5.28 kJ | Candle flame energy |
| 10 BTU | 10,550.6 J | 10.55 kJ | Match stick burn |
| 100 BTU | 105,506 J | 105.51 kJ | Small burner |
| 1,000 BTU | 1,055,060 J | 1,055.06 kJ | Space heater (per hour) |
| 5,000 BTU | 5,275,300 J | 5,275.3 kJ | Small window AC unit |
| 10,000 BTU | 10,550,600 J | 10,550.6 kJ | Medium window AC |
| 12,000 BTU | 12,660,720 J | 12,660.72 kJ | 1-ton air conditioner |
| 24,000 BTU | 25,321,440 J | 25,321.44 kJ | 2-ton central AC |
| 36,000 BTU | 37,982,160 J | 37,982.16 kJ | 3-ton AC system |
| 60,000 BTU | 63,303,600 J | 63,303.6 kJ | Small furnace |
| 100,000 BTU | 105,506,000 J | 105,506 kJ | Large furnace |
A British Thermal Unit (BTU) is a traditional unit of heat energy defined as the amount of energy required to raise the temperature of one pound of water by one degree Fahrenheit at sea level. One BTU equals exactly 1055.06 joules in the International System of Units (SI). Despite its British origins, the BTU is primarily used in the United States for rating heating and cooling equipment, natural gas appliances, and energy consumption.
In the HVAC (Heating, Ventilation, and Air Conditioning) industry, BTU is the standard measurement for equipment capacity. When you shop for an air conditioner, furnace, or space heater in the United States, the capacity rating appears in BTU per hour (BTU/h). A 12,000 BTU/h air conditioner can remove 12,000 BTU of heat energy from a space every hour. This measurement helps consumers and professionals compare equipment performance and determine appropriate sizing for different spaces.
The joule, in contrast, is the SI unit of energy named after physicist James Prescott Joule. One joule represents the energy transferred when a force of one newton moves an object one meter. In thermodynamics, joules measure all forms of energy: heat, mechanical work, and electrical energy. While most of the world uses joules and kilojoules for energy calculations, American HVAC professionals continue using BTU due to industry standardization and consumer familiarity.
Understanding both units is valuable for international engineering work, comparing equipment specifications from different markets, and scientific calculations. The conversion factor 1055.06 joules per BTU allows precise translation between Imperial and metric energy measurements. For HVAC professionals working with international equipment or energy efficiency standards like SEER (Seasonal Energy Efficiency Ratio), converting between BTU and joules ensures accurate performance calculations and compliance with regional energy codes.
Converting BTU to joules is straightforward: multiply the BTU value by 1055.06. This conversion factor is internationally standardized and exact, making calculations reliable for engineering and scientific applications.
Question: An 8,000 BTU window air conditioner removes how many joules per hour?
Question: A 80,000 BTU/h furnace produces how much energy in joules per hour?
Question: A 3-ton (36,000 BTU/h) central AC system equals how many kilojoules?
For rough estimates, remember that 1 BTU is approximately 1,000 joules (actual: 1055). This gives you a quick ballpark figure. For example, 10,000 BTU ≈ 10 million joules or 10 megajoules. This approximation is useful for quick mental calculations, though precise engineering work requires the exact factor of 1055.06.
| AC Type | Capacity (BTU/h) | Energy (kJ/h) | Room Size |
|---|---|---|---|
| Small window unit | 5,000 | 5,275 kJ | 100-150 sq ft |
| Medium window unit | 8,000 | 8,440 kJ | 250-350 sq ft |
| Large window unit | 12,000 | 12,661 kJ | 400-550 sq ft |
| 1.5 ton mini-split | 18,000 | 18,991 kJ | 600-900 sq ft |
| 2 ton central AC | 24,000 | 25,321 kJ | 1,000-1,400 sq ft |
| 3 ton central AC | 36,000 | 37,982 kJ | 1,500-2,100 sq ft |
| 4 ton central AC | 48,000 | 50,643 kJ | 2,000-2,700 sq ft |
| 5 ton central AC | 60,000 | 63,304 kJ | 2,500-3,300 sq ft |
| Heating System | Output (BTU/h) | Energy (MJ/h) | Application |
|---|---|---|---|
| Portable space heater | 5,000 | 5.28 MJ | Single room |
| Wall furnace | 25,000 | 26.38 MJ | Small apartment |
| Small home furnace | 40,000 | 42.20 MJ | 1,000 sq ft home |
| Medium furnace | 60,000 | 63.30 MJ | 1,500 sq ft home |
| Large furnace | 80,000 | 84.40 MJ | 2,000 sq ft home |
| Extra-large furnace | 100,000 | 105.51 MJ | 2,500+ sq ft home |
| Commercial boiler | 200,000 | 211.01 MJ | Small building |
| Industrial boiler | 500,000 | 527.53 MJ | Large facility |
| Appliance | Input (BTU/h) | Energy (kJ/h) | Usage |
|---|---|---|---|
| Gas stove burner | 10,000 | 10,551 kJ | Single burner |
| Gas water heater | 40,000 | 42,202 kJ | Residential |
| Gas dryer | 20,000 | 21,101 kJ | Clothes drying |
| Tankless water heater | 150,000 | 158,259 kJ | On-demand hot water |
| Gas fireplace | 30,000 | 31,652 kJ | Supplemental heat |
| Pool heater | 400,000 | 422,024 kJ | Swimming pool |
Proper equipment sizing requires accurate energy calculations. Engineers converting BTU ratings to joules can perform load calculations using SI units, ensuring systems aren't oversized (wasting energy) or undersized (failing to maintain comfort). International projects especially require conversion between American BTU specifications and metric standards.
Comparing energy efficiency across different measurement systems requires BTU-to-joules conversion. Energy codes and efficiency standards vary by region—some use SEER (BTU/watt-hour), others use metric coefficients of performance. Converting allows apples-to-apples comparisons and compliance verification.
Natural gas bills often show consumption in therms or BTU, while electrical energy appears in kilowatt-hours. Converting BTU to joules (and then to kWh) allows homeowners to compare heating costs between gas and electric systems, calculate total energy consumption, and identify savings opportunities.
Thermodynamics research and engineering publications use joules as the standard energy unit. Converting BTU data from HVAC equipment specifications, building performance studies, or field measurements to joules ensures compatibility with scientific literature, peer review standards, and international collaboration.
HVAC equipment ratings show BTU per hour (BTU/h), which is power. One BTU/h equals 0.293 watts. When converting to joules, consider whether you're converting total energy or power over time.
The exact conversion factor is 1055.06 joules per BTU. While rounding to 1055 or 1000 works for estimates, engineering calculations require the precise value to avoid cumulative errors in large systems.
HVAC capacities in joules create large numbers. Divide by 1,000 to get kilojoules (kJ) for easier reading. For example, 12,000 BTU = 12,660,720 J = 12,660.72 kJ.
One ton of cooling equals 12,000 BTU/h (not related to weight). This comes from melting one ton of ice in 24 hours. A 3-ton AC removes 36,000 BTU/h or 37,982 kJ/h.
Furnaces show input BTU (gas consumption) and output BTU (heat delivered). A 100,000 BTU input furnace at 80% efficiency delivers 80,000 BTU output. Know which value you're converting.
The BTU rating shows theoretical capacity. Real-world performance depends on ductwork, insulation, and maintenance. A 24,000 BTU system might deliver less effective cooling if poorly installed.
While you can convert kWh to BTU (1 kWh = 3,412 BTU), electrical energy is better expressed in kilowatt-hours or joules. BTU is specifically for thermal energy in heating/cooling contexts.
To convert BTU to joules, multiply the BTU value by 1055.06. For example, 10 BTU = 10 × 1055.06 = 10,550.6 joules or approximately 10.55 kilojoules. This conversion factor is based on the international definition where 1 BTU equals exactly 1055.06 joules.
For air conditioning, multiply your room's square footage by 20 BTU per square foot. A 200 sq ft room needs about 4,000 BTU. For heating, consider additional factors like insulation quality, number of windows, ceiling height, and climate zone. Consult an HVAC professional for precise calculations.
BTU/h (BTU per hour) is a unit of power, indicating the rate of energy transfer. Most HVAC equipment is rated in BTU/h, showing how much heating or cooling it can provide per hour. This is equivalent to power in watts (1 BTU/h ≈ 0.293 watts).
BTU remains common in the United States HVAC industry due to historical usage and familiarity among professionals and consumers. While most of the world uses metric units, the American market continues to rate heating and cooling equipment in BTU. Understanding both systems is valuable for international work.
A British Thermal Unit (BTU) is the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit at sea level. In practical terms, one BTU equals about 1055 joules. It's commonly used to rate air conditioners, furnaces, and heating systems in the United States.
Window air conditioners typically range from 5,000 BTU (small room) to 18,000 BTU (large room). Central air systems range from 18,000 BTU (1.5 tons) to 60,000 BTU (5 tons) or more for whole-home cooling. One ton of cooling equals 12,000 BTU/h.
Not necessarily. Higher BTU means more heating or cooling capacity, but oversized units cycle on/off frequently, reducing efficiency and comfort. An undersized unit runs constantly without reaching desired temperatures. Proper sizing based on room volume, insulation, and climate is essential for optimal performance and energy efficiency.
To convert joules to BTU, divide the joule value by 1055.06. For example, 5,000 joules ÷ 1055.06 = 4.74 BTU. Alternatively, multiply joules by 0.000947817 to get BTU directly.
One watt equals approximately 3.412 BTU per hour (BTU/h). To convert BTU/h to watts, divide by 3.412. For example, a 12,000 BTU/h air conditioner uses about 3,517 watts (12,000 ÷ 3.412). Note that BTU is energy while BTU/h is power, similar to joules and watts.
The United States has historically used Imperial units, and the HVAC industry developed using BTU as the standard measurement before the metric system was widely adopted internationally. While other countries use watts or kilowatts for heating/cooling capacity, American manufacturers continue using BTU because it's familiar to consumers and professionals in the US market.
This calculator uses the internationally standardized conversion factor where 1 BTU = 1055.06 joules exactly. For critical HVAC system sizing, equipment selection, or energy efficiency compliance, always consult qualified HVAC professionals and refer to manufacturer specifications and local building codes.