🔥 Watts to Heat Calculator
Convert a device’s electrical power rating in watts into the heat it actually produces over a chosen run time.
What This Calculator Does
Nearly all the electrical power a resistive device (like a space heater, hair dryer, or soldering iron) consumes is converted directly into heat. This calculator converts a watt power rating into the more familiar heating units of BTU/hr and total heat energy over a run time.
The Formula
Since 1 watt equals 1 joule per second, power in watts converts to heat rate in BTU per hour using 1 W = 3.412142 BTU/hr. Multiplying that rate by the run time (in hours) gives total heat output in BTU, and converting watt-hours to kilowatt-hours gives the total energy used. An efficiency setting lets you scale down the result for devices where not all electrical power becomes usable heat (such as motors or lighting).
Note: For a purely resistive heating element, efficiency is effectively 100%. This tool is for general educational and planning purposes and doesn’t model heat lost to ventilation, radiation losses, or a device’s specific design.