Looking for a new air conditioning unit and wondering what size you need for your home?
In Florida, we use our air conditioners more than in the bulk of the country. South Florida is especially hot and humid, so it’s doubly important to get the AC sizing right.
Doing that requires an understanding of BTU ratings, tonnage, the square footage of your home, and all the other factors that could affect the size of the AC unit you need.
Poor AC sizing can lead to inflated energy bills, discomfort in the home, a shorter AC life, and other problems. By the end of this post, you’ll know how to avoid these common issues with an AC installation that keeps your home comfortable and energy-efficient all year round…
WHAT SIZE AC DO I NEED?
The AC size you need depends on multiple factors, the most important of which is the size and layout of your home (for central air conditioners) or room size (for ductless mini-split systems).
You also need to consider the home’s insulation, ceiling heights, orientation, occupant numbers, and more. To install the right size AC, it’s a good idea to book an energy audit with a local HVAC professional to make sure.
Let’s look a little deeper into AC sizing…
STAY COOL ALL YEAR ROUND WITH ONE WAY AIR…
The team at One Way Air installs, services, and repairs all types of air conditioning systems in Southwest Florida. Get in touch with us here for a quote or call 239-233-4356 in emergencies.
HOW ARE AC UNITS SIZED?
Choosing the right size AC unit is a great starting point when shopping for a new air conditioning unit.
With so many different types, brands, models, efficiencies, features, and prices to choose from, homeowners can lose sight of the fact that size is the single most important factor to get right with an AC unit.
WHAT IS AC SIZE?
The size of an AC unit refers to its cooling capacity rather than its physical dimensions. AC units use British Thermal Units (BTUs) to measure this.
One BTU is equal to the amount of energy needed to raise or lower the temperature of one pound of water by 1ºF.
With air conditioning units and heat pumps, the BTU rating refers to the quantity of energy used to remove heat from an area in an hour during the heat transfer process.
So, a 16,000 BTU unit can remove 16,000 BTUs of heat from a space in one hour. A unit of 32,000 BTUs can remove double the amount of heat from the same space in the same period.
Generally speaking, the larger the space, the higher the BTU rating is required with AC units—though other factors can affect this, as we shall see.
DUCTLESS AC SIZE VS. CENTRAL AC SIZE
Around 90 percent of Florida homes have central AC installed, so that’s the focus of this article.
If you’re looking to replace an AC unit, it’s likely a central air conditioning unit, which needs to be more powerful than a ductless mini-split system designed to heat a single room.
Central AC units for Florida homes typically range in size from around 18,000 BTU to 60,000 BTU per unit.
Ductless mini-split systems, on the other hand, may range from around 8,000 to 24,000 BTU per unit.
HOW IS AC TONNAGE CONNECTED TO BTU?
When calculating the cost of a new AC unit in Florida, you may need to factor in tonnage as well as BTU.
Tonnage is not a measure of the unit’s weight but another way to measure its cooling capacity. Fortunately, the tonnage to BTU calculation is simple: one ton = 12,000 BTU. Here are some examples:
|
BTU RATING |
TONNAGE |
|---|---|
|
6,000 BTU |
0.5 Ton |
|
12,000 BTU |
1 Ton |
|
18,000 BTU |
1.5 Tons |
|
24,000 BTU |
2 Tons |
|
30,000 BTU |
2.5 Tons |
|
36,000 BTU |
3 Tons |
|
48,000 BTU |
4 Tons |
|
60,000 BTU |
5 Tons |
|
72,000 BTU |
6 Tons |
WHICH FACTORS AFFECT AC SIZE REQUIREMENTS?
The size of the home is the most important factor when sizing central air conditioning units—and that’s where we start—but other important factors also affect the calculation.
SQUARE FOOTAGE
The size of the home in square feet is the most important measurement when sizing AC units in Florida.
If you don’t know the square footage of your home, simply multiply the length and width of each room in feet and add the total together. The US Department of Energy typically recommends 20 BTU per square foot of living space for homes in the U.S. with standard ceiling heights.
However, with Florida’s heat, humidity, and long cooling season, the calculations here are typically higher:
In Florida, the average home size is around 1,700 square feet, which equates to a central AC size requirement of around 34,000 to 42,500 BTU.
Here’s a basic guide for the standard BTU/tonnage requirements for various home sizes in Florida:
|
APPROX. COOLING AREA |
BTU RATING |
TONNAGE |
|---|---|---|
|
500 sq. ft. |
10,000–12,500 BTU |
1 Ton |
|
1,000 sq. ft. |
20,000-25,000 BTU |
2 Tons |
|
1,200 sq. ft. |
24,000-30,000 BTU |
2–2.5 Tons |
|
1,500 sq. ft. |
30,000-37,500 BTU |
2.5-3 Tons |
|
1,700 sq. ft. |
34,000-42,500 BTU |
3-4 Tons |
|
2,000 sq. ft. |
40,000-50,000 BTU |
3.5-4 Tons |
|
2,500 sq. ft. |
50,000-62,500BTU |
4-5 Tons |
|
3,000 sq. ft. |
60,000-75,000BTU |
5-6 Tons |
OTHER FACTORS TO CONSIDER WITH AC SIZE
Before you head out to buy your ideal AC unit based on your home size, it’s not quite that simple. Other factors affect the AC size you need. The most important ones are outlined below…
Ceiling height
Homes with ceilings over eight feet high may require additional cooling capacity because there is simply more air to remove heat and moisture from.
Insulation
Modern, well-insulated homes may be able to manage with lower cooling capacity than a poorly insulated home because more of the cooled air stays inside the home rather than escaping through the cracks, and less warm air from outside penetrates the walls.
Construction materials
Some construction materials are naturally better insulators than others. Materials like brick, concrete, and stone absorb and slowly release heat, moderating temperature swings, while wooden or drywall-based constructions offer fewer insulation benefits.
Room layout
Multi-level homes may require a zoned AC system while single-level homes are usually fine with a standard central AC setup. However, large, open-plan homes may have different cooling requirements from homes with more enclosed spaces.
Windows/orientation
Homes that are exposed to the hot Florida sunshine for long periods, with many south-facing windows, usually require additional cooling capacity than those that are generally well shaded South-facing windows add heat to the home naturally.
Home occupancy
People create heat (more body heat, cooking, showers, etc.), so a house with multiple occupants often requires a larger air conditioner than a single-occupant home.
Appliances and lighting
Appliances and lighting also generate heat. A home that consistently runs multiple appliances and is well-lit with electrical lighting, like many typical modern Florida homes, will place extra demands on the cooling system if all else is equal.
WHY AC SIZE MATTERS IN FLORIDA…
Florida’s heat and humidity spell hard work for air conditioning systems. Removing so much heat and moisture from the indoor air for so much of the year requires powerful units that are up to the job.
Even high-quality units have a shorter lifespan in Florida than in more temperate climate zones. If you install the size wrong, however, it can lead to more than a short lifespan, such as cooling and comfort issues as well as spiraling energy costs.
An undersized air conditioner will run at maximum power but still not adequately cool the space despite increasing energy costs. An oversized AC unit, on the other hand, will short-cycle, inflate energy bills, and can lead to excessive humidity.
It’s a common mistake to buy the largest AC you can afford. Don’t fall into this trap as it will not cool your home faster or more efficiently. By sizing your AC correctly, you ensure a good balance between cooling power, humidity control, and indoor air quality, while also keeping a lid on energy bills and AC repair bills.
Here’s a summary of the potential issues with oversized and undersized AC units…
UNDERSIZED AC ISSUES:
OVERSIZED AC ISSUES:
AC SIZE AND ENERGY EFFICIENCY
The energy efficiency rating of an AC unit does not directly affect the BTU requirements—but it does impact how much energy the unit uses to deliver its cooling power.
AC efficiency is measured in SEER (Seasonal Energy Efficiency Ratio). A unit with a higher rating consumes less energy than one with a lower rating. Ultimately, look for an AC unit that’s not only the right size matched to the space but also with a high SEER rating to save on overall energy costs.
New residential central AC systems must be rated 15 SEER or higher in Florida to meet the U.S. Department of Energy minimum standards. Remember, even small efficiency improvements can lead to substantial long-term savings here, where we use air conditioning so much.
As a quick estimate, upgrading an air conditioning unit in Florida from SEER 14 to SEER 18 can save over 20 percent on monthly cooling costs. That translates to hundreds of dollars per year for most households.
HOW TO CALCULATE THE RIGHT SIZE AC
If you’re shopping for a new central AC unit, you may want to make some basic calculations to size it but, ultimately, there’s no substitute for reliable professional guidance.
You may know the approximate square footage of your home—if not, work it out by measuring the length and width of each room, multiplying them, and adding the total of all rooms together.
You can then refer to the above tables to work out the required BTU and/or tonnage. For a slightly better estimate, try this:
This will provide a very rough guide. Other factors should be considered, so the only way to accurately calculate the size of your central AC unit is to book an energy audit…
WHAT IS AN ENERGY AUDIT?
An energy audit is a professional assessment of your home’s energy needs, including a “load calculation”.
The load calculation will take into account not only the home’s square footage but also the other key factors outlined above, including the home’s insulation, windows, orientation, ceiling heights, construction materials, occupancy, appliances/lighting, etc.
The official HVAC industry measurement is a Manual J Calculation. This determines the exact heating and cooling needs of a building or room, measured in BTU.
WHY CONTACT AN HVAC PROFESSIONAL FOR AC SIZING AND INSTALLATION?
An HVAC professional from One Way Air can perform a Manual J Calculation and, in doing so, help you select the right size AC for your home.
Your HVAC professional can pass on important energy-saving tips too—for instance recommend the latest high-efficiency models. They can also pass on details of any federal or state-run programs that qualify you for energy rebates when purchasing a new AC, such as the Florida Power & Light rebate program or the Federal Energy Efficient Home Improvement Tax Credit.
Using a professional HVAC company for your AC unit’s installation should be a no-brainer—not only for correct unit sizing but also for ductwork compatibility, airflow balance, and correct refrigerant levels. This will directly affect your indoor air quality, comfort, and ongoing costs.
You can protect your investment, maintain performance, and extend the lifespan of your equipment by booking annual AC maintenance.
FAQs
GET THE PERFECT SIZE AC UNIT INSTALLED…
For an accurate assessment of the AC unit size required and a dependable AC installation, contact an AC professional at One Way Air for an inspection today.
