Everything You Need to Know About BTU Ratings

If you’re researching air conditioners, you’ll likely encounter the acronym BTU. These three letters play an important role in finding the right air conditioner for your home. BTU stands for British Thermal Unit and is a measurement of heat energy. One BTU is the equivalent of the amount of heat needed to raise one pound of water by one-degree Fahrenheit. Air conditioning unit sizes are noted in terms of BTU. The higher the BTU rating, the greater the cooling capacity of the system.

Whether you’re in the market for a new air conditioner or just want to be more informed, we’ve put together this guide to BTU ratings to help you learn more.

Why BTU ratings are important

It’s important that your system has a BTU rating that’s compatible with your home. A system with a BTU that’s too low may be unable to cool your home effectively, because the system will be undersized. This can lead to frustrations with uneven temperature, frequent breakdowns, and more.

On the other hand, a system with a BTU that’s too high can cause problems as well. Bigger isn’t better when it comes to air conditioners. An A/C system that’s too large will cost more money to operate and have a shorter lifespan overall because it will work too hard to heat or cool your home. This places a large amount of stress on the crucial components of the system. The stress makes the components more likely to fail, which in turn leads to frequent and potentially costly repairs.

How to find the right BTU rating for your home

Residential systems usually range from 12,000 to 60,000 BTUs. To find the right BTU rating for your home, factors such as square footage, floorplan, and more must be taken into account.

Square footage

The square footage of your home greatly influences the BTUs needed to cool it effectively. As a general rule, an air conditioner needs around 20 BTUs per each square foot of living space. With that rule in mind, it’s easy to generate a rough guide of BTUs needed depending on square footage.

Square FootageBTUs Needed



Along with how big your home is, its layout and features also play a role in BTU calculation. Homes with high ceilings and open floorplans may require an air conditioner with more BTUs than a home without those features. Additionally, if your home has two stories, the second story will likely require more BTUs to cool effectively due to the fact that heat rises. Rooms that get direct sunlight or that have large windows will also require more BTUs, while rooms that get little sunlight will require less BTUs.


The location of your home also matters when it comes to BTU calculation. Homes in warmer climates will naturally require more cooling capacity than those in milder climates. If your home faces westward and gets a lot of sun, this will play a role as well.

Windows and insulation

A home that’s well insulated, and therefore more energy efficient, will require less BTUs and cooling capacity than a home with poor insulation and significant energy loss. The number of windows in your home mattes as well. According to the U.S. Department of Energy, heat loss and gain through windows is responsible for 25%–30% of residential heating and cooling energy use. Homes with large windows or older, drafty windows will require a system with more BTUs to compensate for energy loss.

Manual J load calculation

While accounting for things like floorplan, windows, and square footage may seem complicated, here at Chas Roberts we take all of the above factors and more into consideration when sizing your air conditioner. It’s all part of what’s called Manual J load calculation, which is used to determine how many BTUs of cooling is necessary. With Manual J load calculation, the experts at Chas Roberts can ensure that your air conditioner is not too big, or too small, but just right for your home.

More terms to know

BTU isn’t the only acronym or industry term you’ll encounter as you shop for a new air conditioner. By familiarizing yourself with common terms to know, you’ll be able to make a more informed purchase.


SEER stands for Seasonal Energy Efficiency Ratio. It measures how efficiently an air conditioner operates in a variety of temperatures and seasonal environments, ranging from 65 to 104 degrees Fahrenheit. A SEER rating is a maximum efficiency rating, similar to the miles per gallon of your car. Every air conditioning system has a SEER rating, usually ranging from 13 to 17, and a maximum of 25. The higher the SEER rating, the more energy efficient the system is.

EER stands for Energy Efficiency Ratio. It’s a standardized measurement that shows how efficiently an air conditioner performs when the outdoor temperature is 95 degrees Fahrenheit. These days, most air conditioners use SEER ratings, but EER ratings can be important when evaluating certain types of systems, such as portable, window, or ductless mini-split units.


CFM, or Cubic Feet Per Minute, is a measurement of airflow volume. It is determined by how many cubic feet of air passes through a specific point in one minute. CPM is key in finding an A/C system that is the right size for your home. A larger home will need a system with a higher CFM, while the opposite is true for a smaller home.

A basic rule of thumb when it comes to CFM is to have one CFM per square foot of living space. A 1,600 square foot home would require a system with a capacity of 1,600 CFM.

Split system

The majority of modern central air conditioning systems are a split system. Split systems have four recognizable components:

  • an outdoor metal cabinet that houses the condenser and compressor
  • an indoor cabinet that holds the evaporator coil
  • an air handler that sends cool air through the duct system
  • a thermostat, programmable or manual, that controls indoor temperature

The indoor and outdoor components of a split system are connected by refrigerant tubing. A split system does not require extensive ductwork, which makes these systems more energy efficient than the other alternative, known as packaged systems. This is because ductwork is a major source of energy use. Split systems also tend to be quieter, and longer lasting.

Packaged system

Packaged units contain all the air conditioning parts in one smaller, more compact system, typically found outside of your home. In packaged units, the air supply and return are in your home’s ductwork which funnels cooled and heated air in and out of your home. Because packaged units are so much smaller than split systems, they tend to be more convenient for those who have less space to install an air conditioner.

A/C questions? Ask Chas Roberts

If you have more questions about finding the right BTU rating for your new air conditioner, or need help with all things cooling and heating, the experts at Chas Roberts are ready to help. Contact us to get started.