What is BTU per hour?

BTU per hour is a unit of power used to measure the heating or cooling capacity of HVAC equipment. It is the standard rating system for air conditioners, furnaces, and heat pumps in the United States.

Real-world uses

BTU per hour is the standard power unit for rating furnaces, air conditioners, heat pumps, and boilers in the United States. A residential central air conditioner might be rated at 24,000–60,000 BTU/h. In casual use, the "/h" is often dropped, so "12,000 BTU air conditioner" actually means 12,000 BTU/h.

History

BTU/h became the standard power unit for the US HVAC industry during the post-World War II residential building boom, as central air conditioning and forced-air heating became widespread. Industry standards bodies such as AHRI codified BTU/h ratings for equipment comparison.

Common mistakes

Dropping the "/h": confusing BTU (energy) with BTU/h (power) is extremely common in HVAC contexts. A unit absorbing 12,000 BTU in one hour is operating at 12,000 BTU/h of capacity. Also, 1 ton of refrigeration = 12,000 BTU/h, which can cause confusion in capacity comparisons.

What is milliwatt?

A milliwatt is a unit of power equal to one thousandth of a watt. It is used in low-power electronics, wireless communication systems, laser specifications, and medical device power ratings.

Real-world uses

Milliwatts measure the power of laser pointers (Class 1: <1 mW; Class 3B: up to 500 mW), Bluetooth radios (typically 1–100 mW), Wi-Fi transmitters, and fibre optic signals. They are used in optical communications, consumer electronics, and medical laser specifications.

History

Milliwatts became relevant as the miniaturisation era brought small electrical and optical devices into widespread use from the mid-20th century. Consumer electronics, telecommunications, and biomedical equipment all required power specifications at this sub-watt scale.

Common mistakes

Confusing milliwatts (mW) with microwatts (µW)—1 mW = 1,000 µW. Also, assuming all laser pointers operate at the same power level; safety regulations classify lasers by output power in mW, and even small increases can be hazardous to the eyes.

When is this conversion used?

Converting between BTU per hour and milliwatt is common when working across metric and imperial systems, such as international trade, travel between countries with different measurement standards, or following instructions from a different region.

Worked examples

1 BTU per hour = 293.07107 milliwatt

1 milliwatt = 0.001 watt

How to convert BTU per hour to milliwatt

To convert BTU per hour to milliwatt, multiply the value by 293.07107.

To convert milliwatt back to BTU per hour, multiply by 0.00341214.

Measurement standards

The watt is the SI derived unit of power, defined as one joule per second (kg·m²/s³). Horsepower remains in widespread informal use, particularly in the automotive industry, but has no single universal definition across regions.

Did you know?

The human body at rest produces about 80 watts of power — roughly enough to keep an incandescent light bulb glowing. During intense exercise, a trained cyclist can sustain over 400 watts, and elite sprinters briefly exceed 2,000 watts.

Quick reference: BTU per hour to milliwatt

Common values

Available Power units

• watt conversions
• kilowatt conversions
• horsepower (mechanical) conversions
• megawatt conversions
• gigawatt conversions
• milliwatt conversions
• microwatt conversions
• BTU per hour conversions
• kilocalorie per hour conversions
• ton of refrigeration conversions

More BTU per hour conversions

• Convert BTU per hour to watt
• Convert BTU per hour to kilowatt
• Convert BTU per hour to horsepower (mechanical)
• Convert BTU per hour to megawatt
• Convert BTU per hour to gigawatt
• Convert BTU per hour to milliwatt
• Convert BTU per hour to microwatt
• Convert BTU per hour to kilocalorie per hour
• Convert BTU per hour to ton of refrigeration

Assumption: horsepower values use mechanical horsepower.