Understanding Horsepower (Electric) and BTU per Hour
Horsepower (electric) is a unit of power defined as exactly 746 watts. It is commonly used to rate the output of electric motors, generators, and certain types of heating equipment. In practical engineering contexts, the electric horsepower is preferred over mechanical horsepower when dealing with electrically driven systems because the conversion to watts is exact and uniform.
BTU per hour (BTU/hr) is a unit of power that measures the rate of heat transfer. One BTU is the amount of energy required to raise the temperature of one pound of water by one degree Fahrenheit. BTU/hr is widely used in the HVAC industry to specify the heating or cooling capacity of furnaces, boilers, air conditioners, and heat pumps.
The conversion factor between these two units is derived from the watt equivalence:
This precise factor is essential when converting motor power ratings to equivalent heat flows, such as when sizing electric heaters that will be driven by a motor or when calculating the heat rejected by an electric motor in an enclosed space.
A common formula used is \(\text{BTU/hr} = \text{hp (electric)} \times 2545.4582677917633\).
Horsepower (Electric) to BTU per hour Conversion Reference Table
Horsepower (Electric) (hp)
BTU per hour (BTU/hr)
0.1
254.5458
0.5
1272.7291
1.0
2545.4583
2.0
5090.9165
5.0
12727.2913
10.0
25454.5827
20.0
50909.1654
50.0
127272.9134
100.0
254545.8268
500.0
1.2727e+06
1000.0
2.5455e+06
Step-by-Step Conversion: 10 hp (Electric) to BTU/hr
Step 1: Start with the value in horsepower (electric): 10 hp.
Step 2: Multiply by the conversion factor (2545.4582677917633 BTU/hr per hp).
Step 4: Round to a practical number of decimal places if needed. For most engineering applications, 25454.58 BTU/hr is sufficient.
Electric horsepower is defined as exactly 746 W, while mechanical horsepower is approximately 745.7 W. The difference is small (about 0.04%), but in precise engineering calculations—especially when cumulative heat loads are involved—using the correct definition avoids errors. Since most modern motors are rated in electric horsepower, that unit is the standard for electrical-to-thermal conversions.
Yes, but only as a starting point. The horsepower rating of a compressor (often given in electric hp) can be converted to BTU/hr to estimate the heat pumping capacity. However, actual capacity depends on operating conditions (evaporator/condenser temperatures) and system efficiency (COP or EER). The conversion gives an ideal heat flow equivalent; real-world equipment ratings are always lower due to thermodynamic and mechanical losses.
"On fait la science avec des faits, comme on fait une maison avec des pierres ; mais une accumulation de faits n'est pas plus une science qu'un tas de pierres n'est une maison." "Science is built up of facts, as a house is built of stones; but an accumulation of facts is no more a science than a heap of stones is a house." — Henri Poincaré (French Mathematician, Theoretical Physicist & Mining Engineer)