If you’re considering installing an HVAC system in your home for the first time or replacing an existing AC unit, you may be wondering what size you actually need. It probably seems like an easy question to answer with a quick internet search. But the truth is, there are a lot of different factors to be considered in choosing the right size air conditioner. It’s our mission to make sure our customers are fully informed and comfortable when making decisions like these. If you want to attempt a rough estimate for the sizing of your HVAC unit, keep reading.

How AC Unit Size and Energy Efficiency are Measured

You’ve probably heard of BTU and maybe even BTUh, but what do they actually mean? What does a “ton” mean when referring to an HVAC unit?

Cooling Capacity

Air conditioners have either a BTUh or BTU rating, which are units of measure for cooling capacity.

  • BTUh (British Thermal Unit per hour) is a measurement of an air conditioner’s cooling ability in an hour, also known as “tons.”
  • BTU (British Thermal Unit) is the amount of energy that is required to increase the temperature of a pound of water by one degree Fahrenheit.


Seasonal Energy Efficiency Ratio, or SEER, indicates an air conditioner’s energy efficiency, or how much energy it uses. This efficiency rating is the total amount of cooling provided during the entire cooling season, divided by the total amount of electrical energy used.

Some units may have an ENERGY STAR® certification which means it uses at least 8% less energy than conventional models and have extra energy savings. Overall, the higher the SEER rating, the more energy-efficient the unit is.

Why Size Matters

An improperly sized air conditioner will have trouble keeping your home at a comfortable temperature. Yes, even one that is too large. That’s right, an undersized AC isn’t the only one that can cause problems. AC size is one of those things you really need to get just right.

It’s easy to assume that bigger is better if you have no knowledge of how an HVAC system works. You may think that the system will not have to work as hard to cool your home if it’s bigger than the space requires. This is a common misconception and a mistake that a reliable HVAC contractor will not allow you to make. It’s important to install the right size AC for your home to avoid several problems.

Problems with an oversized ac unit

  • Oversized air conditioners may experience frequent short cycles because of how quickly they cool the space. A perpetual short cycle actually increase your energy bills, decrease the life of the unit, and increase maintenance requirements.
  • An AC unit that is too large may cause cold spots throughout the home.
  • A larger system than necessary may not be able to dehumidify your home’s air effectively. Running in short cycles means that it won’t run long enough to effect humidity levels. This can cause even more problems like mold and poor air quality throughout your home.

Problems with undersized ac unit

  • An AC system that is too small will raise your energy costs because it will have to run longer to cool the space.
  • Insufficient air conditioner size can cause hot spots throughout your home since the system will struggle to cool every room.
  • Undersized units will result in a shorter lifespan and more repairs.
  • The almost constant running of your AC unit will over-dehumidify your home, drying out the air to an uncomfortable extreme.

What Size AC Unit Do I Need in Naples, Florida?

Home size is not the only factor to consider when calculating the proper air conditioning sizing. There are actually quite a few additional factors to be considered. Air conditioning is basically a math problem that must be calculated to get a correctly sized air conditioner. Below are some things that will factor into those calculations.

Variables that could impact the size unit you should choose

All of these variables should be considered by HVAC experts before you purchase a cooling unit.


When it comes to air conditioning, a hot climate will work your central air unit much harder than a more mild climate. Those of us in a sub-tropical climate like southwest Florida will benefit from an outdoor unit with a higher SEER rating so our desired temperature can be maintained with better energy efficiency.

Home exterior

The type of material on the exterior surface of your home may either insulate your home from the heat of the sun, or absorb that heat. Dark colors will absorb more heat, while light colors will reflect it.

Sun exposure and shade

Homes that face south or west typically take longer to cool because of the heat from direct sun exposure during the summer. On the other hand, homes facing primarily north or east tend to be cooler. Homes that don’t have much shade from trees or other buildings may also be more difficult to cool.

Insulation and windows

A well-insulated home will make it easier for your HVAC equipment to do its job. That means a poorly insulated home may need a slightly higher BTU unit than the square footage calls for. Otherwise, in the long run, you may end up with an overworked system that will cause you other problems.

Ceiling height

High ceilings have more volume of space to cool and require a higher number of BTUs for best results. A good rule of thumb is to calculate one or two BTUs higher than what is recommended for the square footage of the room.

Heat generating appliances

The amount of heat that your appliances put off also makes a difference in the BTUs needed to cool the room and the size of the unit you’ll need.

How To Calculate The Correct Size Unit For Your Home

All you need to get a rough estimate for the size AC unit you will need is the square footage of your home. Even though calculating the proper size unit for the size of your home is easy, we recommend consulting an HVAC technician to review the considerations above. An experienced HVAC dealer will know how to adjust for those considerations after your actual square footage is calculated.

Calculating your home’s square footage:

Measure the size of the room, length and width. Multiply the length times the width of each room in your home, then add them together. Once you have the square footage, multiply it by 25 to get the BTUhs needed to cool your space.

Calculating the AC load:

The AC load is the total amount of output required to cool a home. Your technician will use a residential load calculation to determine the total AC unit load required for your home in order to recommend the right size of the AC unit for your home. The calculation looks like this:

  • (square footage) x (ceiling height) x 20 BTUs
  • (number of occupants) x 100 BTU
  • (number of entry doors) x 1,000 BTU
  • (number of windows) x 1,000 BTU

Contact the HVAC Professionals for Proper Air Conditioner Sizing

As leaders in the HVAC industry in our community, we take these things seriously. We do “comfort on porpoise” which means we don’t take shortcuts and we make sure to get our customers set up with the best possible solution for cooling their homes. Our reliable and knowledgeable HVAC technicians will give you a detailed free estimate for a new AC unit, including full and accurate measurements, testing, and calculations for the size and type of system you need. They will also let you know if you don’t actually need a new system but instead need a repair.

You have questions now, but you will feel nothing but informed and satisfied after walking through the estimate process with the professional staff a Dolphin Cooling and Heating. Even if you’re just shopping around right now, contact us to experience the Dolphin difference!

Are you wondering if it’s actually time for a replacement? Find out when you should replace your HVAC unit.

“My family and I have used Dolphin for many years and they never fail to disappoint. As a former service manager of a car dealership I understand how important it is to treat people properly and everyone from top to bottom at Dolphin “gets” this concept.” – Bob

“I highly recommend Dolphin Cooling & Heating to my family and friends. They are trustworthy, efficient, friendly, and have reasonable prices. I have been using them as my AC provider for the past 2 years and wouldn’t want to go anywhere else.” -Erica Peavy

“The technicians were extremely knowledgeable, professional, and friendly. Excellent communication with advance text notifications of their arrival. They saved us money by researching the warranty on a part they didn’t even install. We are thrilled we found Dolphin Cooling and Heating and will be recommending them to anyone looking for an honest, reliable, and responsive HVAC company.” -Amanda Yonkin