kW to BTU/hr Calculator
Convert kW to BTU/hr for HVAC, heaters, and chillers. 1 kW = 3,412.14 BTU/hr. Live calculator with exact constant and worked examples.
Common conversions
| Input | Result |
|---|---|
| 0.5 kW | 1,706 BTU/hr |
| 1 kW | 3,412 BTU/hr |
| 1.5 kW | 5,118 BTU/hr |
| 3.5 kW | 11,942 BTU/hr |
| 4.5 kW | 15,355 BTU/hr |
| 5 kW | 17,061 BTU/hr |
| 7.5 kW | 25,591 BTU/hr |
| 10 kW | 34,121 BTU/hr |
| 15 kW | 51,182 BTU/hr |
The math behind it
- BTU/hr = 6 × 3412.142
- BTU/hr = 20,472.85
Everything you need to know
The British Thermal Unit per hour (BTU/hr) is the standard capacity rating for heaters, air conditioners, and chillers sold in North America. One BTU is the energy needed to raise one pound of water by 1°F, and the constant 3,412.142 converts electrical kilowatts into that thermal unit exactly.
BTU/hr, tons, and kW: how they relate
Central air conditioners and heat pumps are often rated in tons of cooling rather than BTU/hr or kW. One ton equals 12,000 BTU/hr, which equals 3.517 kW. A "3-ton" residential AC unit moves about 36,000 BTU/hr, or 10.55 kW of heat, out of the house. Converting between all three units means multiplying or dividing by the same 3,412.142 constant, then dividing by 12,000 to get tons.
Sizing heaters, chillers, and AC units
HVAC contractors size equipment to match a calculated heat load, usually derived from a Manual J calculation that accounts for square footage, insulation, window area, and climate zone. A BTU/hr rating that's too low leaves a space undercooled on the hottest days; one that's too high causes short cycling, poor humidity control, and higher electricity bills. Converting a heater's or chiller's kW rating to BTU/hr lets you compare it directly against a room's calculated load or a spec sheet that only lists BTU/hr.
Electrical input versus thermal output
For simple resistive heaters (electric baseboard, space heaters, water heater elements), the kW-to-BTU/hr conversion is exact: every watt of electricity becomes a watt of heat. Heat pumps and air conditioners break that assumption. A mini-split rated at 12,000 BTU/hr of cooling might draw only 1 kW of electricity, because its coefficient of performance (COP) multiplies the electrical input by roughly 3 to 4x. Don't assume a device's BTU/hr rating equals its electrical draw in kW unless the spec sheet confirms the device is purely resistive.
Common applications
Spec sheets for baseboard heaters, space heaters, and garage heaters often list capacity in BTU/hr. Convert your room's calculated kW heat-loss figure to BTU/hr so it matches the units printed on the box.
IT heat loads are usually tallied in kW from nameplate power draw. Converting to BTU/hr lets a CRAC or CRAH vendor quote a properly sized cooling unit, since HVAC cooling capacity is almost always sold in BTU/hr or tons.
Pool and spa heaters are sold with BTU/hr input ratings. Estimate the pool's heat loss in kW from surface area and desired temperature rise, then convert to BTU/hr to shop for a matching heater.
Replacement heating elements are rated in kW, usually 4.5 or 5.5 kW for standard 240 V tanks. Converting to BTU/hr shows the recovery rate, meaning how many gallons per hour the element can reheat.
Common mistakes
BTU is a unit of energy; BTU/hr is a unit of power. HVAC nameplates almost always mean BTU/hr even when the label just says 'BTU,' so never mix the two in a calculation.
The straight kW × 3,412.142 formula only holds for resistive heat. A heat pump with COP 3.5 delivers far more BTU/hr of heat than its electrical kW input alone would suggest, and a gas furnace below 100% AFUE delivers less usable heat than its BTU/hr input rating.
A rule of thumb like '20 BTU/hr per square foot' ignores insulation, window area, ceiling height, and climate zone. Two identically sized rooms can have heat loads that differ by 50% or more; use a proper Manual J calculation for anything beyond a rough estimate.
A 12,000 BTU/hr mini-split doesn't pull 3.5 kW from the wall. Divide the rated BTU/hr by the unit's COP or EER to estimate actual electrical consumption, typically 1 to 1.2 kW for that size unit.
Frequently asked questions
How many BTU/hr is 1 kW?+
3,412.14 BTU/hr. This is an exact unit conversion (1 kWh = 3,412.14 BTU), so it applies fully whenever electrical energy converts entirely into heat, as in resistive heaters.
How many kW is 12,000 BTU/hr?+
About 3.517 kW. 12,000 BTU/hr equals one ton of cooling capacity, the standard unit for rating central air conditioners.
How many kW does a 24,000 BTU air conditioner use?+
Roughly 2 to 2.4 kW of electricity, not 7 kW. The 24,000 BTU/hr figure describes cooling output; a typical unit with a COP around 3 to 3.5 needs far less electrical input than a direct BTU/hr-to-kW conversion suggests.
Is a bigger BTU rating always better for a room?+
No. Oversizing a heater or AC unit makes it cycle on and off too quickly, which wastes energy and leaves humidity poorly controlled. Match the BTU/hr rating to a proper room heat-load calculation instead of buying the largest unit available.
Does the kW to BTU/hr formula change for gas furnaces?+
No, the 3,412.142 factor is a fixed physics conversion, but gas furnace ratings describe fuel input, not electrical kW. A furnace rated at 80,000 BTU/hr input at 80% AFUE only delivers about 64,000 BTU/hr of usable heat.
How do I convert BTU/hr to tons of cooling?+
Divide by 12,000. A 36,000 BTU/hr system equals 3 tons, which also equals 10.55 kW using the 3,412.142 conversion factor.
Why do US HVAC systems use BTU instead of watts?+
It's a holdover from imperial units that the North American HVAC industry never fully replaced. Nameplates, ductwork sizing charts, and contractor tools all use BTU/hr, so converting from kW keeps your numbers compatible with US equipment specs.
What's the BTU/hr rating of a typical electric water heater element?+
A common 4.5 kW element produces about 15,355 BTU/hr of heat, which sets how fast the tank recovers after a draw of hot water.
Do I need to account for efficiency when converting kW to BTU/hr?+
Yes, for anything other than resistive heat. Resistive heaters convert kW to BTU/hr at 100% efficiency. Heat pumps, air conditioners, and combustion furnaces all have efficiency factors (COP or AFUE) that change the relationship between input power and delivered heat.