Kilowatts to BTU/hr Calculator
HVAC equipment is rated in BTU per hour. The electrical circuit feeding it is rated in kilowatts. Neither figure converts to the other on its own, and a spec sheet rarely does that arithmetic for you.
That mismatch shows up on nearly every HVAC job: a manufacturer's cut sheet lists a mini-split's capacity in BTU/hr, while the disconnect, the breaker and the panel schedule all speak in kilowatts and amps. A contractor swapping in a 3.5 kW mini-split system needs to translate that electrical rating into the BTU/hr figure a homeowner actually recognizes, or work the other direction, from a target BTU/hr load back to the kW the electrical side has to support.
BTU/hr = 3.5 × 3412.14 = 11,942.49 BTU/hr
Why the two numbers don't line up automatically
A kilowatt measures electrical power, the rate energy is being consumed. A BTU per hour measures thermal power, the rate heat is being moved or produced. The conversion factor between them, 3412.14 BTU/hr per kW, is a fixed physical unit conversion, unrelated to any specific brand of equipment or how efficiently it operates.
That fixed factor is exact for a load that turns electricity directly into heat, such as baseboard heat or electric furnace strip heat, nearly all the input energy converts to output heat, so multiplying kW by 3412.14 lands close to the real BTU/hr figure. A heat pump or an air conditioner compressor breaks that assumption on purpose: its whole job is to relocate more heat energy than the electricity it consumes, which is exactly what its SEER, EER or COP rating describes. Multiplying that unit's electrical kW rating by 3412.14 still gives a correct unit conversion, but not the unit's actual rated cooling or heating capacity, which comes from the manufacturer's spec sheet instead.
As a rough illustration only, a unit with a nameplate EER of roughly 12 delivers somewhere near 12 BTU/hr of cooling for every watt of electricity it draws, several times what the straight 3412.14 conversion alone would suggest. That ratio varies by model, outdoor temperature and load condition, so it belongs to the specific unit's spec sheet rather than a fixed constant, and no rule-of-thumb EER figure should replace reading the actual rating off the equipment.
Where 3412.14 comes from
One watt equals 3.412142 BTU/hr, so one kilowatt equals 3412.14 BTU/hr. Multiplying a kilowatt figure by that constant converts it to BTU/hr; dividing a BTU/hr figure by the same constant converts it back to kilowatts.
HVAC equipment is also commonly rated in tons of refrigeration rather than BTU/hr directly: one ton is a fixed 12,000 BTU/hr, so dividing a BTU/hr figure by 12,000 gives the tons figure printed on most residential AC and mini-split nameplates.
The calculator's swap button runs the same math in reverse, turning a target BTU/hr figure (a manufacturer's minimum cooling requirement for a room, say) back into a kilowatt figure. That reverse figure is only a straight unit conversion too, so treat it the same way: a reliable estimate for a resistive electric heat source, and a starting reference point rather than an electrical-draw estimate for a heat pump or compressor-driven system.
Worked example: a 3.5 kW mini-split system
Electrical rating of 3.5 kW, converted to a BTU/hr figure and then to tons of refrigeration.
- 1
Apply the formula
BTU/hr = 3.5 × 3412.14
- 2
Solve
BTU/hr = 11,942.5 BTU/hr
- 3
Convert to tons of refrigeration
11,942.5 / 12,000 ≈ 0.995 tons
This is a straight unit conversion of the electrical rating, not a substitute for the unit's rated cooling or heating capacity: for a heat pump or AC compressor, that capacity depends on its SEER/EER/COP rating and belongs on the manufacturer's spec sheet, not on this arithmetic alone.
Common mini-split and AC sizes, kW to BTU/hr
Straight unit conversion at 3412.14 BTU/hr per kW. For a heat pump or AC compressor, treat this as a reference figure alongside the equipment's own rated capacity, not a replacement for it.
| Rating | BTU/hr |
|---|---|
| 1 kW | 3,412.1 BTU/hr |
| 1.5 kW | 5,118.2 BTU/hr |
| 2 kW | 6,824.3 BTU/hr |
| 2.5 kW | 8,530.4 BTU/hr |
| 3.5 kW * | 11,942.5 BTU/hr |
| 5 kW | 17,060.7 BTU/hr |
| 7 kW | 23,885.0 BTU/hr |
| 10 kW | 34,121.4 BTU/hr |
* The worked example above. Reference figures only, not measured or rated values. Confirm any real unit's capacity against its own nameplate or spec sheet.
Related heating and cooling maths
Questions
Kilowatts to BTU/hr FAQ
Sizing questions that come up once an electrical kW rating has to be weighed against a unit's actual cooling or heating capacity.
Does a heat pump's electrical kW rating tell you its cooling capacity?
Not directly. A heat pump or AC compressor moves more heat energy than the electricity it consumes, so its rated BTU/hr capacity is a separate, efficiency-dependent number rather than the electrical draw run through a unit-conversion factor. That gap is exactly what SEER, EER and COP ratings describe. A unit's manufacturer cut sheet lists the actual rated cooling and heating capacity in BTU/hr; treat that figure, not a multiplied-out electrical rating, as the real answer for sizing.
What's the difference between a heat pump's input power and its output BTU/hr?
Input power is the electricity the unit consumes, measured in kW on the nameplate and the electrical panel; output BTU/hr is the rate of heat it moves into or out of a space, measured on the equipment spec sheet. For a resistive electric heater the two track closely, because nearly all the input energy converts straight to heat. For a heat pump the output is typically several times the input, since a compressor relocates existing heat rather than generating it from scratch. That ratio is the unit's COP or EER.
Why does oversizing an air conditioner backfire?
An oversized unit satisfies the thermostat too quickly, so it short-cycles, running in brief bursts instead of long, steady cycles, and short cycles do not run long enough to properly dehumidify the space. The result is often a room that reads as "cold and clammy" rather than comfortable, along with more wear from the extra start-stop cycling on the compressor. Manufacturer sizing tools and a room-by-room load calculation exist precisely to avoid guessing a BTU/hr figure that is larger than what the space needs.
How does a ton of refrigeration relate to BTU/hr?
One ton of refrigeration is a fixed definition equal to 12,000 BTU/hr. It has nothing to do with the physical weight of anything, and originates from the cooling effect of melting one ton of ice over 24 hours. It's the unit HVAC equipment is commonly sold in (a "2-ton" or "3-ton" central AC system), so dividing a BTU/hr figure by 12,000 converts a capacity rating into the tons figure most contractors and homeowners recognize.
What does "1.5 ton" actually mean in kilowatts?
1.5 tons of cooling capacity is 1.5 × 12,000 = 18,000 BTU/hr, which converts to 18,000 / 3412.14 ≈ 5.275 kW of thermal capacity, a measure of heat moved, not the unit's electrical draw. The actual electricity a 1.5-ton unit pulls from the panel is much lower than 5.275 kW, because a heat pump or AC compressor moves more heat energy than it consumes electrically. Check the nameplate's electrical rating separately from its tonnage for panel and breaker sizing.
Is an electric resistance heater's BTU output the same as this calculator's math suggests?
Close to it. A baseboard heater or electric furnace strip heat converts nearly all its electrical input straight to heat, so multiplying its kW rating by 3412.14 is a reasonable estimate of its BTU/hr output. That is the one case where the straight unit-conversion factor and the equipment's real-world output roughly line up. A heat pump or AC compressor is the opposite case: its rated BTU/hr comes from the spec sheet, not from multiplying its electrical kW rating by 3412.14.