Before we dig into individual conversions, here's the master reference table with every HVAC-relevant conversion factor in one place.
Master BTU Conversion Reference Table
| Convert From | Convert To | Multiply By | Source |
|---|
| 1 kW | BTU/hr | 3,412.14 | NIST / EIA |
| 1 BTU/hr | kW | 0.000293 | NIST / EIA |
| 1 Watt | BTU/hr | 3.41214 | NIST / EIA |
| 1 BTU/hr | Watts | 0.29307 | NIST / EIA |
| 1 Ton (cooling) | BTU/hr | 12,000 (exact) | ASHRAE |
| 1 BTU/hr | Tons | 0.0000833 | ASHRAE |
| 1 kWh | BTU | 3,412 | EIA |
| 1 BTU | kWh | 0.000293 | EIA |
| 1 Therm | BTU | 100,000 (exact) | US legal def. |
| 1 BTU | Therms | 0.00001 | US legal def. |
| 1 HP (mech.) | BTU/hr | 2,544.43 | NIST |
| 1 BTU/hr | HP | 0.000393 | NIST |
| 1 MJ | BTU | 947.817 | NIST |
| 1 BTU | Joules | 1,055.06 | NIST SP 811 |
What Is a BTU (British Thermal Unit)?
A British Thermal Unit (BTU) is a traditional unit of heat energy. One BTU equals the amount of heat required to raise the temperature of one pound of liquid water by one degree Fahrenheit. It's roughly the energy released by burning a single wooden match.
The standard BTU used in HVAC engineering is the International Table BTU (BTUᵢₜ), adopted at the Fifth International Conference on Properties of Steam in London, 1956. One BTUᵢₜ equals exactly 1,055.05585 joules.
In HVAC, we almost always mean BTU per hour (BTU/hr) when we say "BTU." An air conditioner rated at 24,000 BTU removes 24,000 BTU of heat energy from your home every hour. This is a rate of energy transfer — or power — not just a quantity of energy.
How to Convert BTU to kW (and kW to BTU)
The kilowatt (kW) is the standard unit of power used across Europe, Asia, and most of the world. In the US, HVAC systems are rated in BTU/hr. Here's how to convert between them.
kW = BTU/hr ÷ 3,412.14
BTU/hr = kW × 3,412.14
Key fact: 1 kW = 3,412.14 BTU/hr. This is the single most important HVAC conversion factor. If you remember only one number from this page, make it 3,412.
BTU to kW Quick Reference Table
| BTU/hr | kW | Common Equipment |
|---|
| 6,000 BTU/hr | 1.76 kW | Small window AC |
| 9,000 BTU/hr | 2.64 kW | Mini-split (small room) |
| 12,000 BTU/hr | 3.52 kW | 1-ton AC / large mini-split |
| 18,000 BTU/hr | 5.27 kW | 1.5-ton AC |
| 24,000 BTU/hr | 7.03 kW | 2-ton AC |
| 36,000 BTU/hr | 10.55 kW | 3-ton AC |
| 48,000 BTU/hr | 14.07 kW | 4-ton AC |
| 60,000 BTU/hr | 17.58 kW | 5-ton AC |
If you're comparing AC units, you can also use our AC tonnage calculator to determine the right cooling capacity for your space (/ac-tonnage-calculator).
How to Convert BTU to Watts (and Watts to BTU)
For smaller equipment like space heaters and baseboard heaters, watts are the standard rating. The conversion is the same as kW, just without the "kilo" (thousandths) step.
Watts = BTU/hr ÷ 3.41214
BTU/hr = Watts × 3.41214
Key fact: 1 Watt = 3.412 BTU/hr. A standard 1,500-watt space heater produces 5,118 BTU/hr of heat output. That's a very common question (and a very useful number to remember for sizing electric heaters).
For a deeper look at electric heater costs, check our guide on the cost to run an electric heater (/cost-to-run-electric-heater).
Watts to BTU Quick Reference Table
| Watts | BTU/hr | Common Equipment |
|---|
| 500 W | 1,706 BTU/hr | Small personal heater |
| 750 W | 2,559 BTU/hr | Low-setting space heater |
| 1,000 W | 3,412 BTU/hr | Medium space heater |
| 1,500 W | 5,118 BTU/hr | Standard space heater |
| 2,000 W | 6,824 BTU/hr | Baseboard heater |
| 3,000 W | 10,236 BTU/hr | Large baseboard / wall heater |
| 5,000 W | 17,060 BTU/hr | Garage heater |
| 10,000 W | 34,121 BTU/hr | Commercial / 10 kW unit |
How to Convert BTU to Tons of Cooling (and Tons to BTU)
In the US and Canada, air conditioner capacity is almost always described in "tons." This has nothing to do with weight. One ton of refrigeration equals the rate of heat removal needed to melt one short ton (2,000 lb) of ice in 24 hours.
Tons = BTU/hr ÷ 12,000
BTU/hr = Tons × 12,000
Key fact: 1 Ton = 12,000 BTU/hr = 3.517 kW. According to ASHRAE Terminology, a ton of refrigeration is defined as a "time rate of cooling equal to 12,000 BTU/h (approximately 3,517 W)." This standard dates back to the 1880s ice trade and was formalized by the precursor to ASHRAE in 1903.
Need to figure out how many tons your home actually needs? Use our how many BTU AC guide (/how-many-btu-ac) or the heating BTU calculator (/heating-btu-calculator) for furnaces.
Tons to BTU to kW Conversion Table
| AC Size (Tons) | BTU/hr | kW | Typical Home Size |
|---|
| 1 Ton | 12,000 BTU/hr | 3.52 kW | 400-700 sq ft |
| 1.5 Ton | 18,000 BTU/hr | 5.27 kW | 700-1,000 sq ft |
| 2 Ton | 24,000 BTU/hr | 7.03 kW | 1,000-1,300 sq ft |
| 2.5 Ton | 30,000 BTU/hr | 8.79 kW | 1,300-1,600 sq ft |
| 3 Ton | 36,000 BTU/hr | 10.55 kW | 1,600-2,000 sq ft |
| 3.5 Ton | 42,000 BTU/hr | 12.31 kW | 2,000-2,400 sq ft |
| 4 Ton | 48,000 BTU/hr | 14.07 kW | 2,400-2,800 sq ft |
| 5 Ton | 60,000 BTU/hr | 17.58 kW | 2,800-3,500 sq ft |
How to Convert BTU to kWh (and kWh to BTU)
This is an energy-to-energy conversion (not power). A kilowatt-hour (kWh) is the unit on your electric bill. BTU is the unit on your gas bill. Here's how they connect.
kWh = BTU ÷ 3,412
BTU = kWh × 3,412
Key fact: 1 kWh = 3,412 BTU. This conversion is essential when comparing gas heating costs to electric heating costs. If natural gas costs $1.00 per therm (100,000 BTU) and electricity costs $0.15 per kWh (3,412 BTU), you can directly compare the cost per BTU of each fuel.
We use this exact conversion in our heating cost calculator (/heating-cost-calculator) and cost to run an air conditioner guide (/cost-to-run-air-conditioner).
How to Convert BTU to Therms (and Therms to BTU)
A therm is the standard billing unit for natural gas in the United States. It's a simple, exact conversion.
Therms = BTU ÷ 100,000
BTU = Therms × 100,000
Key fact: 1 Therm = 100,000 BTU (exactly, by legal definition). When you see your gas bill showing "5 therms," that means your furnace consumed 500,000 BTU of natural gas energy.
If your gas furnace has an AFUE rating (/afue-rating) of 90%, only 90% of those BTU actually heat your home — the rest goes up the flue. A furnace rated at 80,000 BTU input with 90% AFUE delivers 72,000 BTU of useful heat output per hour.
How to Convert BTU to Horsepower
Horsepower shows up occasionally in HVAC, especially for large commercial compressors and boilers.
HP (mechanical) = BTU/hr ÷ 2,544.43
BTU/hr = HP × 2,544.43
Key fact: 1 Mechanical HP = 2,544.43 BTU/hr. Note that boiler horsepower is completely different: 1 Boiler HP = 33,471 BTU/hr. Don't confuse the two.
Common HVAC Equipment BTU Conversions
Here's a practical reference showing real-world HVAC equipment and their BTU, kW, and watt equivalents.
Air Conditioners and Heat Pumps by Tonnage
| Size | BTU/hr | kW | Watts |
|---|
| 1 Ton | 12,000 | 3.52 | 3,517 |
| 1.5 Ton | 18,000 | 5.27 | 5,275 |
| 2 Ton | 24,000 | 7.03 | 7,034 |
| 2.5 Ton | 30,000 | 8.79 | 8,793 |
| 3 Ton | 36,000 | 10.55 | 10,551 |
| 4 Ton | 48,000 | 14.07 | 14,069 |
| 5 Ton | 60,000 | 17.58 | 17,586 |
For detailed heat pump sizing, see our heat pump sizing calculator (/heat-pump-sizing).
Electric Heaters (Watts to BTU)
| Heater Type | Watts | BTU/hr Output |
|---|
| Personal space heater | 500 W | 1,706 BTU/hr |
| Standard space heater | 1,500 W | 5,118 BTU/hr |
| Baseboard heater (4 ft) | 1,000 W | 3,412 BTU/hr |
| Baseboard heater (6 ft) | 1,500 W | 5,118 BTU/hr |
| Baseboard heater (8 ft) | 2,000 W | 6,824 BTU/hr |
| Wall heater | 2,000-4,000 W | ,824-13,649 BTU/hr |
| Garage/shop heater | 5,000 W | 17,060 BTU/hr |
Electric heaters are 100% efficient at point of use — every watt of electricity becomes heat. That means 1,500 W always equals 5,118 BTU/hr, regardless of the heater brand or type. For wattage context, see our generator sizing guide (/generator-sizing).
| Furnace Input | AFUE | BTU Output/hr | Therms Input/hr |
|---|
| 40,000 BTU/hr | 80% | 32,000 BTU/hr | 0.40 therms/hr |
| 60,000 BTU/hr | 90% | 54,000 BTU/hr | 0.60 therms/hr |
| 80,000 BTU/hr | 80% | 64,000 BTU/hr | 0.80 therms/hr |
| 80,000 BTU/hr | 96% | 76,800 BTU/hr | 0.80 therms/hr |
| 100,000 BTU/hr | 90% | 90,000 BTU/hr | 1.00 therms/hr |
| 120,000 BTU/hr | 96% | 115,200 BTU/hr | 1.20 therms/hr |
The difference between input and output BTU is the furnace's AFUE efficiency. Use our furnace sizing calculator (/furnace-sizing-calculator) to find the right size for your home, and learn more about AFUE ratings (/afue-rating) to understand how efficiency affects your gas bill.
Why Does HVAC Use Different Units in Different Countries?
The short answer: history. The BTU originated as a British unit of heat measurement in the 19th century. When the US HVAC industry formalized standards in the early 1900s, BTU and tons of refrigeration became the default. The rest of the world adopted the metric system's kilowatt.
The US remains the largest HVAC market globally, which is why manufacturers continue to list BTU as a primary rating even on equipment sold internationally. European and Asian manufacturers rate equipment in kW, following the International System of Units (SI).
In practice, you'll encounter both. A Daikin mini-split might be listed as 3.5 kW in Europe and 12,000 BTU in the US — same unit, different label. The UK officially replaced therms with joules for natural gas billing in January 2000, but "BTU" is still used informally in UK air conditioning.
ASHRAE publishes all standards in both I-P (inch-pound/BTU) and SI (kW) units, so either system is valid for engineering purposes.
Worked Examples
Example 1: Converting a 2-Ton AC to BTU and kW
Let's say you're shopping for a central air conditioner and the contractor recommends a 2-ton unit. What does that mean in BTU and kW?
Step 1: Multiply tons by 12,000.
2 Tons × 12,000 = 24,000 BTU/hr
Step 2: Convert BTU/hr to kW by dividing by 3,412.14.
24,000 ÷ 3,412.14 = 7.03 kW
Result: A 2-ton AC has a cooling capacity of 24,000 BTU/hr or 7.03 kW.
Example 2: Converting a European 8 kW Heat Pump to BTU
You're looking at a European heat pump rated at 8 kW heating capacity. How does that compare to US units?
Step 1: Multiply kW by 3,412.14.
8 kW × 3,412.14 = 27,297 BTU/hr
Step 2: Convert to tons by dividing by 12,000.
27,297 ÷ 12,000 = 2.27 Tons
Result: An 8 kW European heat pump equals roughly a 27,297 BTU/hr or 2.3-ton US unit. You can fine-tune this with our heat pump sizing calculator (/heat-pump-sizing).
Example 3: Converting a 1,500W Electric Heater to BTU Output
A standard electric space heater draws 1,500 watts. How many BTU of heat does it produce?
Step 1: Multiply watts by 3.41214.
1,500 W × 3.41214 = 5,118 BTU/hr
Result: A 1,500-watt heater produces 5,118 BTU/hr of heat. Since electric heaters are 100% efficient at point of use, all 1,500 watts become heat. For running cost info, check our cost to run an electric heater guide (/cost-to-run-electric-heater).
Example 4: Converting Gas Furnace Therms to BTU Output
Your gas bill shows you used 50 therms last month. Your furnace has a 96% AFUE rating. How many BTU of useful heat did your furnace actually deliver?
Step 1: Convert therms to BTU.
50 Therms × 100,000 = 5,000,000 BTU (total gas energy input)
Step 2: Apply the AFUE efficiency.
5,000,000 BTU × 0.96 = 4,800,000 BTU (useful heat output)
Result: Out of 5 million BTU of gas energy, your furnace delivered 4,800,000 BTU of actual heat to your home. The remaining 200,000 BTU (4%) was lost as exhaust.
A heat pump consumes 3 kW of electrical input and has a COP of 3.5. What is the total heating output in BTU/hr?
Step 1: Calculate total thermal output in kW.
3 kW input × 3.5 COP = 10.5 kW thermal output
Step 2: Convert kW to BTU/hr.
10.5 kW × 3,412.14 = 35,827 BTU/hr
Result: The heat pump delivers 35,827 BTU/hr (approximately 3 tons) of heating while only consuming 3 kW of electricity. That's the magic of heat pumps — they move heat rather than generating it. Learn more in our COP calculator (/cop-calculator).
Frequently Asked Questions
What is a BTU in HVAC?
A BTU (British Thermal Unit) measures heat energy. In HVAC, we use BTU/hr to describe how much heat an air conditioner removes or a furnace produces per hour. One BTU is the energy needed to raise 1 pound of water by 1°F.
How many BTU are in 1 ton of cooling?
1 ton of cooling = 12,000 BTU/hr. This standard was set by ASHRAE and originates from the ice trade — it's the rate of heat removal needed to melt one short ton (2,000 lb) of ice in 24 hours.
How do I convert BTU to kW?
Divide the BTU/hr value by 3,412.14. For example, 24,000 BTU/hr ÷ 3,412.14 = 7.03 kW. To go from kW to BTU, multiply by 3,412.14.
How many BTU does a 1,500-watt heater produce?
A 1,500-watt electric heater produces 5,118 BTU/hr. Multiply watts by 3.412 to get BTU/hr. Electric heaters convert 100% of electricity to heat, so the conversion is exact.
What is the difference between BTU and BTU/hr?
BTU is a unit of energy (like a gallon of gas). BTU/hr is a unit of power (like miles per hour). When HVAC manufacturers say "12,000 BTU," they almost always mean 12,000 BTU/hr — the rate at which the equipment transfers heat.
Why do some countries use kW instead of BTU for HVAC?
The US and Canada use BTU because the HVAC industry standardized on this unit in the early 1900s. Most other countries use kilowatts (kW) as part of the metric International System of Units (SI). Both are valid — ASHRAE publishes standards in both systems.