Convert BTU to Watts: The Formula and When to Use It

One BTU per hour equals approximately 0.2931 watts. To convert BTU/hr to watts, multiply by 0.2931; to convert watts to BTU/hr, multiply by 3.412. This conversion applies to the rate of thermal energy transfer. It does not, by itself, tell you the electrical wattage a heater or air conditioner draws from the wall, which is a separate spec.

Spec sheets in this industry were written by engineers for engineers, and the same word can mean two different things on the same page. If you have ever stared at a mini split brochure with kilowatts, BTU per hour, and a separate wattage figure all fighting for attention, you already know the problem. For a quick sanity check on room sizing before you dive into unit math, our BTU heater calculator guide is the sensible starting point.

A quick note on where AC Direct fits in this. We sell the equipment (Goodman, Daikin, MRCOOL, Mitsubishi, ACiQ) direct to homeowners and contractors, ship it nationally, and the reader hires an installer to put it in. When you know the conversion cold and read the spec sheet correctly, you buy the right unit the first time, and our convert btu to watts calculator in the learning center handles the arithmetic for you.

What is the BTU to watts formula?

The precise thermal conversion is 1 BTU/hr = 0.293071 watts, and its inverse is 1 watt = 3.412141633 BTU/hr. To go from BTU/hr to watts, multiply. To go the other way, multiply by 3.412. These are the same numbers every HVAC engineer uses; there is no rounded "shortcut" version worth memorizing separately.

Worked examples using the exact factor:

• 5,000 BTU/hr × 0.293071 = 1,465 W (roughly 1.47 kW)
• 12,000 BTU/hr × 0.293071 = 3,517 W (one ton of cooling, roughly 3.52 kW)
• 36,000 BTU/hr × 0.293071 = 10,551 W (three tons, roughly 10.55 kW)
• 1,500 W electric heater × 3.412 = 5,118 BTU/hr of heat output

Notice what those numbers describe. The first three are thermal capacity, meaning the rate at which the machine moves heat into or out of your house. The fourth is different, and this is where readers get sideways.

Why does the conversion exist?

BTU is an imperial thermal energy unit; the watt is the SI unit of power. Both measure the rate of energy transfer when BTU is expressed per hour, so a fixed mathematical relationship links them. The conversion exists because American HVAC equipment is rated in BTU/hr while most of the rest of the world (and every electrical appliance) uses watts.

The National Institute of Standards and Technology defines the watt as the SI unit for all forms of power, including heat flow rate. The British Thermal Unit came from a different tradition: the heat needed to raise one pound of water by one degree Fahrenheit. Both measure the same physical thing. They just measure it in different languages.

Thermal output vs electrical input: know the difference

Converting 12,000 BTU/hr to 3,517 watts describes the rate of thermal energy the equipment moves, its cooling or heating capacity. It does not describe the electricity that unit draws from the wall. A 12,000 BTU/hr mini split does not pull 3,517 W from a receptacle. It pulls a fraction of that, because a heat pump moves heat rather than manufacturing it.

The bridge between the two numbers is efficiency. The ENERGY STAR heat pump program uses two metrics you should recognize on any spec sheet:

• EER (Energy Efficiency Ratio): cooling capacity in BTU/hr divided by electrical input in watts, measured at one fixed operating condition.
• COP (Coefficient of Performance): thermal output divided by electrical input, both in the same units. An electric resistance heater has a COP of 1.0. A heat pump routinely runs 2.5 to 4.0 or higher.

The math falls out cleanly: EER = COP × 3.412. If a 12,000 BTU/hr mini split draws 1,000 W to produce its rated cooling, its EER is 12.0 and its COP for that condition is roughly 3.5. Same equipment, same physics, expressed two ways because two different standards bodies got there first.

Now for the observation that matters when you shop. A 1,500 W plug-in electric heater and an efficient mini split producing the same 5,118 BTU/hr of heat do the same thermal work. The mini split gets there on roughly 500 W of input; the resistance heater needs the full 1,500 W. On your bill, that is a three-to-one difference for the identical amount of warmth in the room.

How to read a spec sheet correctly

On any spec sheet, there are typically two power numbers you care about: the thermal capacity (what the machine delivers to the room) and the electrical input (what the meter charges you for). The trick is knowing which is which, because both may appear as watts or kilowatts depending on the manufacturer's home market.

Electric resistance heaters

Simple case. The listed wattage (say 1,500 W) is electrical input, and because resistance heaters convert electricity to heat at effectively 100%, that same 1,500 W is also the thermal output. Convert it to 5,118 BTU/hr if you want to compare it to a room's heat loss calculation.

Air conditioners and heat pumps

Here you will see multiple numbers. Read them carefully:

• Cooling Capacity or Heating Capacity in BTU/hr, sometimes also shown in kW: this is thermal output.
• Rated Power Input, Power Consumption, or Nominal Input Power in watts: this is what the compressor and fan actually draw.
• SEER2, EER2, HSPF2, COP: the ratio linking the two numbers above under the test conditions defined in AHRI certified performance ratings.

Meet Maria. She is looking at two 10,000 BTU/hr portable ACs. Unit A lists a power input of 800 W; Unit B lists 1,250 W. Same cooling job, different meters running. Maria's first instinct was that the higher wattage meant more powerful cooling. It does not. Unit B just needs more electricity to accomplish the same thermal work. Unit A has an EER of 12.5, unit B lands at 8.0. Over a cooling season, that difference shows up on the bill in a way you notice.

Where the conversion matters when shopping

The conversion matters most where two rating systems collide. That happens more often than you might expect, particularly in mini split shopping.

European vs US equipment

European HVAC data sheets list thermal capacity in kilowatts. American sheets list BTU/hr. A "3.5 kW" mini split and a "12,000 BTU/hr" mini split are describing the same size unit; the numbers only look different because of unit convention. Knowing the conversion lets you compare Mitsubishi documentation from two continents without guessing.

Mini splits and multi-zone systems

Mini split cassettes and heads often list nominal capacity in both BTU/hr and kW, plus a separate electrical input in watts. If you are sizing a multi-zone system, the thermal capacity numbers are what get matched to your room-by-room load. That room-by-room load itself comes from an ACCA Manual J calculation, not from a square footage rule of thumb. The wattage figures tell your electrician what circuit and breaker to run.

Portable heaters and electric radiators

These almost always list watts as input, and because they are resistance devices, that same wattage converts directly to BTU/hr of output. Compare that BTU/hr number to a room's heat loss and you know instantly whether a 1,500 W space heater has any real chance in a 400 square foot room in Minnesota. (Spoiler: it does not.)

Central AC and tons of cooling

The "ton" is a legacy unit that stuck around, so central AC gets sized in tons of refrigeration. One ton equals 12,000 BTU/hr equals 3,517 W of thermal capacity. A three-ton system moves 36,000 BTU/hr; a five-ton system moves 60,000 BTU/hr. Same math, different label.

Quick reference conversions

Here is the table to bookmark. Common HVAC capacities in BTU/hr, converted to watts and kilowatts of thermal output. Use it when reading spec sheets, not when sizing your electrical panel.

BTU/hr (thermal output)	Watts (thermal)	Kilowatts (thermal)
1,000	293	0.29
2,000	586	0.59
3,000	879	0.88
4,000	1,172	1.17
5,000	1,465	1.47
6,000	1,758	1.76
7,000	2,051	2.05
8,000	2,345	2.34
9,000	2,638	2.64
10,000	2,931	2.93
12,000 (1 Ton)	3,517	3.52
15,000	4,396	4.40
18,000	5,275	5.28
24,000 (2 Tons)	7,034	7.03
30,000	8,792	8.79
36,000 (3 Tons)	10,551	10.55
48,000 (4 Tons)	14,067	14.07
60,000 (5 Tons)	17,584	17.58

Values calculated at 1 BTU/hr = 0.293071 W per the standard thermal conversion factor.

Need this for a hydronic project instead of a heat pump? Our radiator btu calculator walks through the sizing side.

Related units you may run into

A few adjacent units show up in the same conversations, and knowing where they fit saves the trouble of re-learning them each spring.

Kilowatt-hours (kWh)

A kilowatt-hour is a unit of energy, not power. It is the total energy consumed when 1,000 W runs for one hour. Your electric bill is denominated in kWh. Watts and BTU/hr describe the rate; kWh describes the total. Seasonal efficiency ratings like SEER2 and HSPF2 use kWh in the denominator because they capture a whole cooling or heating season, not a single test point.

Therms

A therm is 100,000 BTU of heat energy, used in the US to bill natural gas. It is a unit of energy, comparable to kWh. Gas furnace capacity is still rated in BTU/hr; therms only appear on the bill.

Tons of refrigeration

The ton originated as the heat required to melt a short ton of ice in 24 hours. It froze into the vocabulary of American HVAC and never left. One ton equals 12,000 BTU/hr, which equals 3,517 W of thermal capacity. Anything you can express in tons, you can express in BTU/hr and then in watts, without changing the underlying quantity.

Paying for the equipment (and your installer)

Once you have the right size figured out, the next question is usually how to pay for it. AC Direct sells and ships the equipment; you hire and pay your own installer. HVAC financing can cover both the unit and the labor from that installer, which is the part most people do not realize is possible.

Three partners handle different needs:

• Hearth finances the equipment AND the installation together, with 0% APR offers and approvals available from a 550 credit score. This is the one that answers "how do I pay my installer" for a full furnace replacement financing scenario.
• Breeze requires no credit check, and applying does not affect a credit score.
• Affirm offers 0% APR at checkout for qualified buyers.

Terms shift over time, so the financing page is the source of truth on current rates and score thresholds. Read the current hvac financing options there before you build a cart.

Frequently Asked Questions

Is 1 BTU per hour exactly 0.293 watts?

The precise conversion factor is 1 BTU/hr equals 0.293071 watts. Most HVAC references round to 0.2931 or 0.293, which is close enough for equipment sizing. The inverse, 1 watt equals 3.412 BTU/hr, uses the same physical constant expressed the other direction. Both are exact within engineering practice.

Does converting BTU to watts tell me my electricity bill?

No. Converting a unit's BTU/hr capacity to watts gives you the rate of thermal energy it moves, not the electricity it draws. Heat pumps and air conditioners consume far less electrical power than their thermal output would suggest, because they move heat rather than generate it. Check the spec sheet's rated power input separately.

Why does a 1,500 watt heater have the same output as a 500 watt mini split?

A resistance heater converts electricity to heat at a coefficient of performance of 1.0, so its input and output match. A mini split heat pump moves outdoor heat indoors, delivering roughly three units of thermal energy for every unit of electricity consumed. Same room warmth, one-third the electrical draw, thanks to the refrigerant cycle.

How many watts is a 12,000 BTU air conditioner?

Its thermal capacity is 3,517 watts, or 3.52 kilowatts. Its electrical draw from the wall is much lower and depends on efficiency. A typical 12,000 BTU/hr mini split with an EER around 12 draws roughly 1,000 watts of electricity to deliver that cooling capacity under standard test conditions.

What is one ton of cooling in watts?

One ton of refrigeration equals 12,000 BTU/hr, which converts to 3,517 watts (3.52 kilowatts) of thermal capacity. This is the rate at which the equipment moves heat, not the electrical power it consumes. A three-ton central AC has 36,000 BTU/hr of cooling capacity, or roughly 10.55 kilowatts of thermal output.