Why AC Unit Size Matters for Your Home

If you’re shopping for a new air conditioner, you’re probably asking, “What size AC unit do I need?” The size of your air conditioning unit is one of the most important factors to consider. Surprisingly, though, the size of an AC unit doesn’t correspond to the measurements of the unit. Instead, it refers to the unit’s cooling capacity. Purchasing the correct size AC unit ensures it will help you keep cool this summer. Read on to learn how to size an AC unit for a house.

Selecting a properly sized cooling system is essential for comfort, efficiency, and system longevity. If you buy an undersized air conditioner, the equipment may fail to keep up with cooling demand on hot, humid summer afternoons, even when running nonstop. This also increases your energy bills, despite your efforts to save money by purchasing a smaller system

On the other hand, if you buy an oversized air conditioner, it will reach the target temperature too quickly. This short-cycling behavior increases wear and tear, leading to premature breakdowns. Cycling on and off frequently also makes it impossible for the AC to adequately dehumidify your home, leaving you feeling cool but clammy. So how do you determine the correct size of an AC unit for your house?

Factors to Consider When Determining AC Unit Size

The square footage of your space is the main factor for determining the correct size of an AC unit for a house. So to get started, you’ll need to measure the length and width of the room you’d like to cool. Multiply length times width to get the square footage of your room. This can be trickier in rooms that aren’t a simple 4-sided shape, but you can break down the room into shapes where square footage can be easily calculated. From there, add the totals from each shape together to get the full square footage of the room.

However, square footage is far from the only consideration you should make. There are additional factors that affect what size central air or window unit you need. Here’s what to consider when calculating the size of your home AC unit:

Climate: A home in Phoenix, Arizona needs a larger AC unit than a house of the same size located in Northern Michigan.
Number of windows and orientation to the sun: South-facing rooms with a lot of windows heat up much faster and need more cooling power than north-facing rooms. Rooms with a lot of windows and doors will also need more cooling power.
Exterior home color and exterior shade: If your home’s exterior is a lighter color, it will reflect the sun and remain cooler. Similarly, if your home gets plenty of shade from surrounding trees or buildings, you won’t need as large of an AC unit.
Home insulation levels and overall airtightness: The better insulated your home is, the better it is at retaining cooled air, and that means you can get by with a smaller AC unit. That also means that windows, doors, and ductwork need to be airtight.
Ceiling height: If your home has high ceilings, your room holds a larger volume of air, which will require more cooling power.
Internal heat gain: If you use heat-generating appliances and electronics during the day, you need more air conditioning to counteract this heat gain.
Occupancy: The more people who live in your home, the larger the AC unit should be.

Understanding BTUs and Tonnage for AC Unit Size

Once you’ve determined the square footage of your room, and home overall, you can determine what size your home AC unit needs to be. The cooling capacity of an air conditioner is measured in British Thermal Units (BTUs). One BTU is about the amount of heat generated by a birthday candle. There are two types of AC units to compare: window AC units and central air conditioners.The obvious difference is that a window unit has a smaller cooling capacity—generally limited to the room it’s installed in, but can include conjoining rooms without a door—while a central air conditioner is meant to cool the entire house.

You’ll find window units with cooling capacities ranging from about 5,000 to 12,500 BTUs, which indicates the amount of heat the unit can remove from a room per hour. Central air conditioners are much larger, so they’re measured in tons, which is equivalent to 12,000 BTUs. You can determine the tonnage you need in the same way you determine the BTUs you need. Most residential units range from 1.5 to 5 tons, or 18,000 to 60,000 BTUs.

If you’ve ever wondered, “What size AC unit do I need, and should I get a central air conditioner or a window AC unit?” be aware that square footage is the number-one factor. In fact, it’s often the only factor listed in rule-of-thumb guides. On average, an air conditioner needs 20 BTUs of cooling power per square foot of living space. However, smaller areas tend to require more than 20 BTUs per square foot, while larger rooms need less than 20 BTUs per square foot.

Why Professional Assessment of AC Unit Size is Recommended

Do you feel confident about how to size an AC unit? Well, an HVAC professional sure does because they do this all day long. A professional knows exactly what factors to consider, and which variables come into play for your home. For example, a professional will be familiar with Seasonal Energy Efficiency Ratio, or SEER, ratings. A SEER rating measures how efficiently an AC unit cools a particular space during a typical cooling season. This ratio is the cooling output in BTUs to the energy input in watts during a cooling season. The higher the SEER rating is, the more energy-efficient the system is.

Depending on the type of home AC unit you choose, your AC unit also needs to be compatible with your home’s windows or with your ducting. That means it’s essential to understand how to determine the correct size of the unit and how to install the unit properly so it can do its job as efficiently as possible. Getting a professional’s insight into the right size AC unit for your house can be essential to getting the maximum energy efficiency, cooling performance, and cost savings you’d like.

Contact Aire Serv^® For Expert Guidance on AC Unit Size Installation

Now that you know how to size an AC unit, you have a general idea of what type and what size of air conditioner will serve your needs best. That said, to get the most accurately sized AC unit, you need to hire a professional. Cooling experts use Manual J, the industry standard for sizing HVAC systems established by the Air Conditioning Contractors of America (ACCA). This compiles all of the factors outlined above and determines how they affect your home’s overall cooling load to calculate the ideal AC unit size for you.

Since you need a licensed and insured service professional to install your central air conditioner, it makes sense to team up with Aire Serv to ensure you make the most cost-effective purchase for your home. Our HVAC professionals also understand how to diagnose and prevent problems with an existing air conditioner. If you experience excessive or insufficient cooling or strange smells, or your air conditioner keeps tripping your breaker, our technicians have you covered. Even better, you can feel confident trusting all of our work because our services are backed by the Neighborly Done Right Promise^™. We’ll get the job done right.

Ready for a new air conditioner and don’t know where to start? We can help you with AC cost estimates, unit sizing, unit installation, and more. Contact us to learn more, for help choosing your new air conditioner, or to schedule other cooling services. Breathe easier with Aire Serv today!