What does BTU mean? Get the right AC and heating system

Are you looking to buy a new conditioner? Then you must have noticed the manufacturers and sellers mentioning ‘BTU’. More so if you want to buy a portable AC. The term is mentioned sometimes with the name of the product and always in the product description. But what does it mean and why is it important? This post will cover all this information and let you know how BTU matters in cooling so that you can pick the right AC for your house. 


What is the full form of BTU?

BTU is an acronym for British Thermal Unit and is used for measuring heat or thermal energy. Though there is ‘British’ in the name, the unit is used worldwide. It is commonly used; like other units such as inches and pounds.

1 BTU is equal to the amount of energy needed for raising (or lowering) a pound of water’s temperature by 1° F at sea level. BTU is an important factor in HVAC units. This measure is also used by the Department of Energy in the USA. 

BTU measures an appliance’s capability of processing energy to heat or cool a space.

When it is mentioned in relevance to heating and AC units, it refers to how many BTUs the machine would be able to remove from the air in an hour. Thus manufacturers and retailers of heating and cooling devices put a lot of emphasis on it. Therefore, you should also know why you need to care about BTU while purchasing an air-conditioner. 

AC and BTU: What is the correlation?

In an HVAC system, the BTU shows its power. So you should check the package for the BTU/hr rating. That is how much energy (in BTUs), your AC will be able to produce in an hour.  

Any heater with a high BTU rating will have a higher heat output. This means that the heater is powerful and can gradually heat a large space or quickly heat a normal room. This is how the BTU is important for the heater in HVAC. But let’s now come to the cooling factor of an AC.

It is a common misconception that air-conditioners cool a room by simply adding cool air. But what these do is remove the heat from a space to make it cool. There is a compressor system in the AC that absorbs heat using a chemical refrigerant. The heat is then taken out of the room and released outside your home. This whole process is not possible without using energy and here is where the BTU matters as it measures this energy.

In the case of a heater, higher BTU relates to a higher capacity of functioning. And we are talking about the cooling of an HVAC or AC, look at the rating to understand which has more cooling output. Anyhow, a higher BTU rating means a more efficient and powerful appliance.

The BTU is used to determine the SEER rating of a system. This can give an indication of how efficient your system is. While this measurement is not perfect, it can help you to compare AC systems to see which one is the most energy-efficient.

Next to the purchase price of an AC system, you also have to take the running costs into account. The SEER rating can help you with this.

Calculating how many BTUs you need: air conditioner room size

When you want to understand how many BTUs you need, the first thing you should do is measure the room. Find out the dimensions of the space the AC is going to serve and calculate the square footage. Other factors also determine how many BTUs you need, like the ceiling height, the sizes of the windows, if there are any, and how much shade the room gets. Ideally, for every square foot of space, you will need 20 BTUs. 

After calculating the square footage, you have to multiply it by 20. For instance, for a 200 sq. feet room, the best air-conditioner for it should have been capable of producing 4000 BTUs.

 If for any reason you are unable to measure a room, we will share these quick tips as a rule of thumb:

Room sizeBTU of the AC
150 square feet or less5000
150-550 square feet8000
550-800 square feet12000
800 square feet +14000
Reference BTU required per room size

It is good to buy an AC with the correct power. Buying an air-conditioner with a good BTU rating means that it will serve you very efficiently for a long time, and also help you save some money. 

How to choose the best AC for your home?

Now that you are aware of what BTU means for an air-conditioner, you might wonder about which AC is going to be the best for your home. But unfortunately, no one else other than yourself can pinpoint which model is going to be perfect for you. Because different things matter like whether you are single or have a family, the kind of room or home you have, and also the lifestyle you have. 

If you live in a mild climate, we would recommend you to buy a window AC or a portable air-conditioner. But if you live in a hot climate, you can get an HVAC system, which is a centrally-cooling unit. Or you can also get a mini-split AC. 

Both centrally-cooling and mini-split units function almost identically. The difference lies in the ducts. A mini-split AC has no ducts at all and functions without any duct. A central air-conditioner circulates air throughout the space using its ducts. 

Also, if your residence is already equipped with central heating, you should go for a central AC unit. This is because the system will use the ducts that are already there to function.

Both houses which are new or very old might not have any ductwork. If you live in any such building, a mini-split AC system is a better choice for you. This type of AC has both an outdoor condenser, and an indoor air dispersal unit. 

As you can see, the BTU of a system is only one factor in the decision-making process.