Skip to main content
HVAC Education, Ductless Systems

What Size Mini Split Do I Need?

By Ryan Mayes

As ductless mini split systems continue to gain in popularity, more people are asking themselves, “how big of a mini split do I need?” That’s because mini splits are not a one-size fits all proposition and ductless air conditioner cost can vary depending on numerous factors. And while it may be tempting to do your research and make a size determination on your own, it can cost you big if you don’t get it right.

“Sizing” in HVAC refers to the amount of heating or cooling a system can provide per hour. It is expressed in terms of BTU/h, or British thermal units per hour. To determine the properly sized mini split ductless system for your home, find a local Carrier expert to perform a load calculation. Load calculation is an industry term for measuring a home’s square footage and assessing other physical factors, then calculating the right BTU/h to satisfactorily heat and/or cool the home.

A dealer answering a womans question of what size mini split do I need

Your local Carrier dealer has the experience to properly size your mini split system, and offers a variety of mini split indoor and outdoor units to fit virtually any home. While you’re at it, familiarize yourself with ductless air conditioner cost so you can begin to budget for your new system.

Why Is Mini Split Sizing So Important?

A properly-sized mini split system can save energy and keep you comfortable for years. That’s why so many people are asking “how big of a mini split do I need?” Before we get into the details on how to make sure your system is sized correctly, let’s take a closer look at some potential issues associated with improper sizing:

  • Issues with over-sized ductless mini split systems: If the mini split system is too large for the space, this can cause “short cycling” -- a term for when the system turns on and then off very quickly because it heats or cools the space too fast. This can cause increased energy bills, undue stress on system components, frequent mini split repairs, and even system failure. Short cycling can affect your comfort in two ways – uneven temperatures as the system continuously turns on and off, and poor humidity control because a short cycling system doesn’t run long enough to effectively dehumidify the space during hot, humid conditions.
  • Issues with undersized ductless mini split systems: If the mini split system is too small, it will work much harder than a properly-sized system. Because it can’t provide enough cooling or heating for the space, it will run continuously or nearly continuously and may never quite deliver a comfortable temperature. The longer it runs, the more electricity it uses, which drives up your utility bills. In turn, the system will age much more quickly or worse – it may become less reliable, require frequent service, and provide fewer years of operation.

To avoid these issues and enjoy efficient, reliable comfort, find a Carrier expert to determine what size system you need. If you want to get an idea of what size system you’ll need before your local professional arrives, try using our mini split sizing calculator for a close approximation.

Check out our Ductless heat pump solutions

How To Size a Mini Split System

Knowing how to size a mini split system can give you confidence when it’s time to make a choice for your home. Keep in mind, this sizing guide is not intended to replace an expert’s load calculation. It will, however, give you a better understanding of how your local expert determines the proper ductless system sizing, and should give you a good idea of sizes you can expect when they are done.

Ductless mini split systems have an outdoor unit and at least one indoor unit. If you are setting up a multi zone system to provide comfort for your entire home, your outdoor unit will need to be sized for the entire home, while the indoor units will need to be sized for the space they will be heating or cooling. As you work through the process, you might find that the individual indoor units may need to be sized differently due to the differences in square footage and other variables in each room. This will allow the indoor air handlers to supply enough airflow and the indoor coil to deliver the correct temperatures in degrees Fahrenheit.

a dealer explaining to a homeowner how to size a mini split system

Mini Split Sizing Calculator

Let’s take a look at some of the parameters used to calculate what size mini split you may need for your home. Of course, there’s no substitute for the best mini split sizing calculator available -- your local Carrier expert. Here are the basics:

  1. Determine the room size in square feet: For a standard, square or rectangular shaped room, it’s pretty straightforward – measure the length and width of the room and multiply those numbers by each other. For example, a 12-foot by 12-foot room would be 12 x 12, or 144 square feet. For a round room, the calculation is a bit more complicated. Measure the distance between the wall and the center of the room. Multiply that number by itself, then multiply by 3.14159 (π) -- this calculation comes straight from you high school geometry book. As an example, if the distance from the wall to the center of the room is 10 feet, the square footage of the room is 10 x 10 x 3.14159, or 314 square feet.
  2. Convert the square footage into BTUs: To calculate the estimated BTUs needed to heat or cool the room, multiply the room’s square footage by 25. Using the example from above, to find the BUTs needed for a 144 square foot room, 144 x 25 = 3600 BTUs.
  3. Repeat for every room: For each living space you are planning to heat or cool using a ductless mini split, you will need to repeat the calculation.

How Do I Calculate What Size Mini Split I Need?

Determining the right size for a mini split is a nuanced process, and due to this complexity, it's advisable to enlist the expertise of a trained HVAC professional. Factors like square footage, insulation type, ceiling height, and window quantity all contribute to the equation, making a thorough evaluation by an expert crucial for selecting the optimal unit size to ensure effective heating and cooling in your specific home environment.

Additional Factors Impacting Size

Here’s where it gets a little trickier. There are many other factors that can affect a load calculation. Your local HVAC expert will be familiar with these and have a way of re-calculating your estimate based upon these other factors.

Ceiling Height

The size of a room's ceiling has a direct impact on how much space it has and how air circulates within it. If a ceiling is taller, then the room will have more space, meaning that a mini split system with a higher capacity will be needed to properly heat or cool the increased amount of air. It is crucial to properly size a mini split system for rooms with different ceiling heights in order to ensure that heating and cooling is efficient and effective. As a general rule, If a room has a ceiling higher than 8 feet, your HVAC dealer might recommend a mini split system with more BTUs.


The size and capacity needs of HVAC systems are greatly influenced by insulation. A space with good insulation holds conditioned air more efficiently, enabling the HVAC system to function better and use less energy. As a result, when selecting HVAC equipment for a building with excellent insulation, smaller systems may be adequate compared to a poorly insulated structure of the same size. If a house has poor insulation, your HVAC dealer may recommend a mini split system with more BTUs.

Seasonal Climate

In areas with extreme temperatures, whether extremely hot or cold, HVAC systems need to be larger to effectively maintain the desired indoor conditions. For example, in hot climates, air conditioners must have a higher cooling capacity to combat the intense heat, while in colder regions, heaters need more BTUs to counteract the chilly temperatures. Homes in climates where the regular temperature exceeds 90 degrees Fahrenheit may require a mini split system with additional BTUs.

How Many Rooms Can a Mini Split Cool?

For single-family homes, ductless mini split heating and air conditioning systems are most often considered for use in room additions, space conversions, or for older homes with no existing ductwork. If you are looking for a ductless heating and cooling solution for an entire home, it begs the question “how many rooms can a mini split cool?”

Carrier Residential provides a number of different options for ductless heat pumps and air conditioners, with multi-zone heat pumps that can accommodate up to five individual indoor units or zones.

Find the Right Mini Split System for You

Adding a mini split ductless comfort system to your home may seem like a great do-it-yourself project. However, getting it done the right way – including how to size a mini split system and how to properly install it – is best handled by an HVAC professional. Find a Carrier expert today and you’ll be one step closer to improved comfort in your home.

Check out this article and discover what is Ductless AC

Let's chat
- Home-icon