Request a Quote Our Services

Call for Emergency +1 (437) 537-5579
how to size an air conditioner
Follow Us:

Knowing how to size an air conditioner correctly is crucial to getting the most efficient unit for your home. It is key to getting an HVAC system that can provide you with the best performance.


Like how you address the most common problems your AC experiences, choosing the right unit size for your home isn’t an easy task. It would help if you looked into several factors before giving your final verdict. Knowing how to size an air conditioner ensures adequate cooling within your home. It also gives you the best value for every buck you spend.


Below is an extensive guide to help you pick your best air conditioning buddy. These factors help you choose what is best for your home. If you think you still need further explanation, calling your trusted HVAC professional would be your best bet.


British Thermal Unit (BTU)


BTU is a vital factor in determining how to size an air conditioner. 


The British Thermal Unit (BTU) is the energy that a pound of water needs to cool down per Fahrenheit in an hour. The BTU helps verify the ability of your AC to function in a given size and space. More so, the air conditioner’s capacity’s unit of measurement is tons. Tons specify the amount that your air conditioning system can cool. 


The golden rule is to have an air conditioning unit with 20 BTU per square foot of the space where you will install it. It means that you can’t be using the same air conditioner you use in a 40 square-meter room in a 60 sq. meter one and expect the same level of cooling. To roughly calculate this, take note of the total square footage of the area, multiply by 25, divide by 12,000 and then diminish .5.


Climate and Weather


Climate and weather directly impact the temperature of your home. These factors are essential in knowing how to size an air conditioner appropriately.


If your home’s location is severely hot and constantly exposed to humidity, you can’t be using the same air conditioner size as a homeowner living in a cooler climate does. Because temperature is directly affected by these factors, it also affects how your air conditioner functions. It determines how much cool air your HVAC unit needs to produce. It would be best to consider this before you decide on getting a little or big-sized AC.


Height of the Ceiling


The height of your ceiling is crucial in knowing how to size an air conditioner.


Don’t expect enough cool air if you have a home with higher ceilings and you’re using a small-sized air conditioning unit. Those two don’t match at all. Higher home ceilings require larger air conditioning units to give adequate cooling. As you expand the space, in this case, the height of the enclosure, you also increase the extent to which the cool air travels. For this reason, you will also need to consider the volume, not just the square area.


If you have a low-lying ceiling, you have a lesser area to fill. A small air conditioning unit will do the trick for you by then.


Number of People


Want to know how to size an air conditioner correctly? Another factor is basing it on the number of people in your home. 


As the number of occupants within an air-conditioned space increases, the amount of heat in the indoor air also increases at the same time. When we inhale oxygen, we release carbon dioxide (CO2) upon exhaling. CO2 is known to soak up infrared energy, manifesting as heat. When you have an expanded number of people within the same space, you also increase the heat within the room. As a result, the level of cooling felt would be different for a group of six than for a group of three. You can observe this in malls when you stroll by on a typical day compared to when the holidays are approaching. 


Buying a small air conditioner for eight people will be ineffective, but purchasing a big unit for a room with just a couple is overkill. The general guide is that if you have more than two regular occupants, add 600 BTU per additional one. It helps you get the right amount of cool air for everyone to enjoy.




Windows are vital factors in determining how to size an air conditioner for your home.


A homeowner must consider the window types before deciding on the AC’s size. Compared to walls, windows are more susceptible to leaking energy inside an enclosed space. For this reason, a room with five windows will need a different cooling capacity than a room with just one. You also have to do an in-depth check of the window’s size. Huge window framings could also affect the level of the cooling power of an AC. So you might need to get a different unit size when your windows are more prominent than standard. The last question you need to ask yourself is if your windows have proper seals. Do they still have gaps, or are they tight and secure when you close them? Even the tiny holes could trigger energy to flee, straining your AC unit more to reach the desired temperature.


Knowing the design and build of your windows help you in getting what unit you need for your home. It helps you from making a wrong purchase and, at the same time, getting the most out of your money.

To wrap things up


Knowing how to size an air conditioner isn’t an easy task. However, it is a vital step to make when choosing your residence’s HVAC partner.


Purchasing a large air conditioning unit for a small space would not be cost-wise. It could lead to short cycling, which could wear and tear your air conditioner and increase your bills. At the same time, getting a small unit for a large room won’t get you anywhere. It can only lead to higher power consumption since your HVAC system will make strenuous efforts to cool a bigger space. You won’t get adequate cooling and could trigger overheating of the unit’s parts.


Knowing your home and its needs is crucial before purchasing an air conditioning unit. All the factors mentioned above help you get a more efficient air conditioning system for your household. Not only to provide you with a more comfortable home but also to help you save money. If you’re still unsure of what to get, an expert’s advice will never hurt.


Learning Resources

Latest News and Inspirational

Please take advantage of our blog posts that answer your questions and help you learn about our products and services.