The Homeowner’s Guide to Central Air Conditioning

Everything You Need to Know About Central Air

Have you ever wondered what exactly people mean when they talk about central air conditioning? Or maybe you’re in the market for a new central air conditioner? Here are the basics of central air, and how to choose a system that works for your needs.

How Does Central Air Work?

A central air conditioner cools in a single location, then distributes that cooled air throughout the house using a series of fans and ducts. When connected to the home’s furnace, the combined central heating and cooling is frequently called “forced air.”

Central air conditioning is an alternative to room air conditioners, such as window units or ductless mini-splits, which cool only the area directly around them.

Types of Central Air Conditioning

Heating and cooling terminology can be confusing because many terms mean different things to a pro or a homeowner. For example, did you notice that in our definition of central air, we didn’t mention how the air is cooled? Systems such as evaporative coolers and geothermal units also cool air in a single location and pump it throughout the house, but they are not normally considered central air conditioners.

So when discussing central air conditioners, we’re really looking at refrigerant-based systems that circulate the interior air of the home. These come in two basic types: split or packaged units.

The “classic” central air conditioner is a split unit, with a compressor and condenser on the outside of the house and the evaporator coils on the inside. It usually uses the same air handling unit (the air intake and fan) as the furnace. Split units make up the bulk of central air conditioners in U.S. homes.

Packaged units encase the air conditioning and air handling unit in a single cabinet, often located outside. They can also be packaged with the furnace or heat pump, making them ideal for homes with limited indoor space.

How to Choose a Central Air Conditioner

The primary factors to consider when choosing a central air conditioner are efficiency, functionality and sizing.

Efficiency is the easiest to put a number on. All air conditioners have a Seasonal Energy Efficiency Ratio (SEER). The higher the SEER, the more energy efficient the AC unit. The exact savings you’ll see with a higher SEER depend on your usage and the climate where you live.

The functionality of a central air system is largely controlled by your thermostat. If you want a system that integrates with your smartphone or virtual voice assistant, look for a smart thermostat. You may also want to consider features such as motion sensors or remote temperature sensors. These allow your HVAC system to view your home as a full unit, rather than just the room where the thermostat is located.

Sizing is extremely important in choosing the right air conditioner, but it’s also the most complicated to discuss. An air conditioner that’s too small for a home will run constantly, while a unit that’s too big will cool your house too fast and turn off before it completes a full cycle. This “short cycle” doesn’t give it time to remove the humidity from the air. That inefficiency not only makes the home feel warmer, but it’s more expensive to run. (For a deeper look at this dip in efficiency, check out this fact sheet from Energy Star.)

A perfectly-sized air conditioner will cool your house to the desired temperature, then turn off until it’s needed again. That complete cycle is the key to lowering your energy bills.

Unfortunately, sizing is complicated. A pro will perform what’s known as a Manual J calculation to determine the proper AC size for your home. This calculation takes into account the region where you live, your home’s size, the AC SEER rating, type of insulation, number of windows and doors and sun exposure.

It’s possible to ballpark the size of AC you need using the square footage of your home, but it’s essential to factor in the local climate. Your best bet is to consult with a HVAC installer near you.

Central Air Cost and Installation

Central air costs vary with the size of the home and the extent of any existing air ducts. Older homes with radiators or electric floorboard heat would need extensive work, while homes with forced air furnaces have a much simpler upgrade.

On average, a new central air conditioner will cost between $4,000 and $7,000 installed.

A central air conditioning installation is usually best left to a licensed pro. Although AC can be installed by a DIYer with sufficient experience, the number of required skills and the potential for voiding a warranty through improper installation means it’s usually wiser to hire out the job.

Central Air Warranties and Repair

A new central air conditioner should be expected to last about 20 years. So select a manufacturer who warranties their equipment, and an installer who will be around to help with any potential problems with the mechanicals and electronics.

Most central air systems are relatively low maintenance. The easiest and most important maintenance item is to change the filter as needed. A filter will last one to six months, depending on the filter type and whether you have a houseful of pets or are allergy sensitive.

Other maintenance includes cleaning the exterior unit and interior duct system as needed. Expect to pay $150 to $200 a year for maintenance and repairs unless you choose to do the work yourself.