What Size AC Unit Do I Need?

November 30th, 2022
Island Comfort technician installing the correct ac unit size

Picking an AC unit for your home takes time, knowledge, and awareness of what size works best for your home. It’s more than just picking a brand and knowing the square footage of your home. One important factor when asking, “What size AC unit do I need?” is that you need to do your research. Getting the right type and size of AC is essential for ensuring your home stays comfortable without complications. 

The wrong-size AC unit can cause many complications in your home, the least of which is a rising energy bill. Air conditioning is not a cheap investment. It is important to get the right size and type to fit your home. Choosing the right size system for your living space saves money, time, and stress. A properly-sized air conditioning system runs efficiently and smoothly, and your electricity bill will thank you.

What Size Air Conditioner Do I Need?

So, if you’re wondering, “What size air conditioner do I need?” There are several steps in the process when deciding what size AC unit to buy. The first of which is deciding what type of air conditioner you need. There are three main types of air conditioners: Ductless AC, packaged AC, and split-system AC. They all work similarly but have differences that affect how your home is cooled. 

  • Split System AC: The most common air conditioning type in Hawaii is the split system air conditioner. It is split because it has an indoor and outdoor unit that works in tandem to cool your home. There are many options to choose from with this type of AC unit. Your Island Comfort HVAC technician can help you select one that fits your specifications for size, efficiency, price, and noise level. 
  • Ductless AC: This AC type has one outdoor unit that connects to one or more units indoors. The indoor units only cool one room, so these systems work best for people who need different temperatures in different rooms. The individual units are mounted to the wall, ceiling, or floor and control the temperature in each separate room. 
  • Packaged AC: The packaged AC system consists of a single outdoor unit. All the operating parts, such as the evaporator coil, compressor, and condensing coil, are in one outside unit. It uses the building’s ductwork to cool your home. There are a few different kinds of packaged AC systems depending on your needs and desire for energy efficiency. 

Air Conditioner Ratings

After picking the kind of system that meets your needs and fits your home, it’s time to look at ratings. Each style of AC unit is rated for different cooling capacities and efficiency. A unit’s cooling capacity is measured in British Thermal Units per Hour (BTUh) or in tons. The energy efficiency is rated with the Seasonal Energy Efficiency Ratio (SEER).

BTUh Rating

  • The BTUh measures how much energy your air conditioner uses to remove heat from your home in one hour. It is measured in terms of tonnage. The cooling capacity of one ton is equal to 12,000 BTUh. Home air conditioners have a tonnage rating that falls within half-ton increments. The scale is from 1.5 to 5-ton units. A 2,000-foot home would likely need a 3 or 3.5-ton unit. However, this varies depending on the climate of the area you live in. 

SEER Rating

  • The SEER rating measures a unit’s average cooling season output divided by the total energy used. The less energy that is used, the higher the SEER rating is. This measures the maximum efficiency of a unit, not the average efficiency. The average SEER rating is 14 or 16, but there are units that have up to 22 SEER ratings. The higher SEER units tend to have two stages or variable cooling stages.  

Other Factors

It is important to pick a unit with the ratings that fit your size home and energy efficiency needs. These help you decide what kind of air conditioning unit is best for you. If you aren’t exactly sure what to choose, speak to your Island Comfort technician. They can help you determine the right style and size of AC based on several different characteristics. Factors include:

  • Ductwork quality 
  • Insulation quality 
  • Direct sun exposure quantity 
  • Number of residents 
  • Usage of heat-generating appliances
  • Climate and average temperatures in your area 
  • Quality and number of windows and exterior doors
  • Home construction materials like brick or wood
  • Features that modify indoor temperatures, like a four seasons room or a fireplace

Manual J Calculation

If you would like to receive specific guidance, your local HVAC dealer can perform an energy audit called a Manual J Calculation. Some utility companies even offer these audits for free. The Manual J Calculation considers many factors, including the ones listed above. Based on these factors, they recommend a correct AC size. The audit is a great way to be absolutely sure what size of unit you need.

AC Unit Size Matters

You might be wondering why it’s so imperative to have the right AC unit size. An air conditioning system does its job no matter how big or small the unit is, right? Wrong. If the unit is too large or too small, you will constantly struggle to balance your indoor climate. You will also probably end up loaded with unexpected energy bill costs. 

If your unit is too small for your home, the air conditioning will run constantly. Despite being on all the time, the air will most likely never feel cold enough. It won’t be powerful enough to get the job done. The system also never gets a chance to turn off. You might even experience uneven cooling, where one room is much cooler than another. 

If your unit is too large, it can strain the unit by constantly switching on and off. The air conditioning will turn on, cool down the house quickly, and then turn off again. The constant repetition of on and off again wears on the unit. This strains the system and causes it to give out much sooner than necessary. 

AC Unit Size Calculator Size Chart

Not everyone is quite ready to buy an AC unit yet. Some people are simply exploring their options and looking for a general idea of what to get. If you aren’t at the point of being ready for an energy audit, you can use the size chart. The AC unit size calculator gives you a basic idea of what to look for in an AC unit.

Your local climate and individual home characteristics affect your final decision. The size chart shouldn’t be the final say on what to get, but it does provide a good rule of thumb.

BTU selection chart based on square footage

You can also find Air Conditioner Size Calculators online to determine the btu per square foot your home requires. It is important to talk to a professional before making a final decision. They can point out the details and make adjustments to help you find the right size AC for your home. 

Island Comfort AC Services

Island Comfort Air Conditioning is a family-owned and operated AC and heating company on Oahu and Kauai. Our goal is to ensure your comfort comes first. We replace, maintain, and repair your air conditioning to help you stay cool in the humid island air. Contact us today to learn more about how our services can benefit you.