What Is BTU in Air Conditioning And Why Do I Need To Know?

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While shopping for an air conditioner, you may have noticed the acronym BTU and wondered, “What is BTU in air conditioning?”

While you do not have to know how air conditioners work to understand BTUs, it does help. In short, air conditioners cool a space by energy transfer—they remove heat from your indoor air and blow it outside. Air conditioners remove humidity through a system of fans and coils. They replace hot air with cool air that passes through ductwork before circulating in the home.

How do BTUs factor into air conditioning? If you purchase an AC unit without understanding its BTU rating, you may be disappointed in its performance and unwittingly shorten its lifespan.

Read on to learn everything to need to know to make an educated decision when shopping for an air conditioner.

What Does BTU Stand For?

So, what is BTU in air conditioning? BTU stands for British Thermal Unit, which is a unit of measurement that describes the energy needed for an air conditioner to remove heat from a room per hour. The AC unit’s BTU rating will guide you in choosing the most appropriate unit for your home.

The BTU pertains to more than just an air conditioner. BTU serves as a global metric that measures the amount of energy needed to raise the temperature of one pound of water by one degree Fahrenheit. In this context, BTU also measures energy transfer for heat pumps, cooking devices, furnaces, and other cooling or heating appliances. The higher the BTU rating, the larger, heavier, and more expensive the unit.

Recommended BTU By Room Size And Use

Home with square footage to help measure correct BTU in air conditioning

Sizing an air conditioner for a room does not refer to its physical dimensions or weight. “Sizing” an AC unit refers to choosing the correct number of BTUs.

The main factor in calculating BTUs is your home’s square footage. The number of BTUs must match the size of the space to cool the room. In the most general terms, a 150-square-foot room (10’x15’) would require an AC unit with a BTU of up to 5,400. For a 200-square-foot room (10’x20’), the recommended BTU is around 6,000. Rooms larger than 300 square feet will require units with at least 8,000 BTU.

Other significant factors go into calculating the cooling power you need for your space. Kitchens or any room where appliances or other equipment generate heat require a higher BTU than the standard recommendation. As a rule of thumb, add 4,000 BTU to the recommended BTU for a kitchen AC unit to maintain the desired temperature.

Ceiling height and room layout also impact the required BTU level. If your home has high ceilings add 10% to the recommended BTU output. If you live in a warmer climate, you should plan on an additional 10-20% more BTUs for each room.

BTU Recommendations Based On Square Footage:

If you are still unsure what BTU level you need for your air conditioning, refer to the BTU chart below. These general BTU recommendations should point you in the right direction:

Recommended BTUs by Square Footage
Room SizeRecommended BTUsRoom SizeRecommended BTUs
150 sq. ft.5,000 BTUs700 sq. ft.14,000 BTUs
250 sq. ft.6,000 BTUs1,000 sq. ft.18,000 BTUs
300 sq. ft.7,000 BTUs1,200 sq. ft.21,000 BTUs
350 sq. ft.8,000 BTUs1,400 sq. ft.23,000 BTUs
400 sq. ft.9,000 BTUs1,600 sq. ft.25,000 BTUs
450 sq. ft.10,000 BTUs1,900 sq. ft.28,000 BTUs
550 sq. ft.12,000 BTUs2,700 sq. ft.36,000 BTUs

Bigger Is Not Always Better

Do not assume that the higher the BTU rating, the more efficient the unit. If your air conditioner has a BTU rating that exceeds the recommendation for the room size, the unit will cool the space too quickly, causing the unit to cycle off prematurely and start up again shortly. These fitful cycling spurts overwork the AC unit’s compressor, shortening its lifespan. An air conditioner with a higher than needed BTU will also not efficiently dehumidify the room.

Conversely, an air conditioner with a too-low BTU will not effectively bear the heat load. The unit will operate nonstop without reaching the desired temperature.

You will save time, aggravation, and money by knowing your square footage and following the BTU recommendations before purchasing an air conditioner.

Additional Points To Consider

AC unit for larger home

While BTU recommendations based on square footage provide sufficient guidelines, refer to these additional considerations when calculating the correct BTU.

  • Second-story spaces tend to run warmer than rooms on the ground floor. The same holds for large-windowed rooms that get direct sunlight. In these situations, you may need to add as much as 10% to the BTU recommendation.
  • Conversely, if you plan to cool a room with limited sun exposure, you may want to subtract 10% from the BTU recommendation.
  • If a space accommodates two or more people at a time, consider adding around 600 BTUs for each additional person.
  • The square footage guidelines in this article pertain to closed or confined spaces. If your space extends to a second room without a door, recalculate the BTU using the square footage of both rooms. For example, to cool an open-concept kitchen that flows into the living space, you need to combine the square footage of both rooms to accurately calculate the BTU.

What Is the Bottom Line With BTUs?

You want to find the most energy-efficient unit with adequate cooling power for your space while keeping energy costs low. Understanding the BTU rating and making the necessary calculations helps you choose the best system for your needs.

Contact Us

Confident Comfort Heating and Cooling is the premier AC company in Flagstaff, Munds Park, and Bellemont. Our team has the expertise to advise you on the best air conditioner for your home. We offer installation, repair, and maintenance services on all kinds of AC units.

Fill out our contact form to get a quote.