Plumbing Tips

What Size Air Conditioner
Do I Need for my Home?

Choosing the Right Size Air Conditioner

Choosing the type and kind of central air conditioning system to install in your home's heating ventilation and air conditioning (HVAC) system is complicated. There are many physical factors about your home's cooling at play that directly affect the performance quality, efficiency, and the cost of how well a central air conditioning system will work in your home. You also must consider the wide variety of central air conditioning systems, as well as their size, efficiency, and installation requirements. So, it's no wonder that homeowners can get anxious when they want to know what size air conditioner they need for their home.

The Chill Cycle

Central air conditioning uses a compressor and condenser coil housed in an outside unit and an expansion valve and evaporator (also called an "A coil") mounted above the furnace heater inside your home's HVAC system. Air conditioning works by cycling refrigerant from gas to liquid and then to gas again through the use of pressure. The refrigerant (known as R-410A) begins the cycle as a low-pressure, low-temperature gas. It enters the outside unit where it's first compressed into a high-pressure, high-temperature gas. Next it enters the condenser's coil where the fan cools the gas into a high pressure liquid. The liquefied refrigerant flows through tubing inside your home to the HVAC unit. There it first enters the expansion valve which limits the flow of the liquid as it enters the evaporator. This valve lets the liquid expand inside the evaporator coil into a gas, chilling to about 7 degrees Celsius as air from the HVAC blower moves over the coil. The refrigerant then heads back to the outside unit as a low-temperature, low-pressure gas to begin the cycle again. Air is cooled by being blown over the chilled coil, and it's then circulated throughout your home. The AC system continues running until the desired temperature is reached. Any humidity in the air condenses onto the coil as water and drips into a condensation pan. In this way, your home is both cooled and de-humidified by a central air conditioning system.

Why Size Matters

Choosing the correct size of your air conditioner is a key a factor for setting up a home cooling system. Sizing an air conditioner requires a consultation with a professional Energy Management Consultant who looks at the factors that effect your home's cooling:

? Total volume of the home's living space - not just the square footage.
? The area of sun-exposed exterior walls.
? The number, age, condition, orientation of windows - do your windows face south?
? The amount of sunshine on your home.
? The age of your home's construction.
? Degree of air sealing the amounts of insulation.
? Existing ventilation system and ductwork - are they right?
? Amount of shade from trees and shrubs.


Likewise, it's not a simple matter of dropping-in any air conditioning system. The size is very important because the correctly sized air conditioner should run a proper full cycle and ensure your home stays cooler longer.

An over-sized AC system will quickly over-cool the air in your home and shut off too soon. However, the building structure itself (walls, wood, furniture, etc.) will not be cooled adequately and allow heat and humidity to creep back in, and the AC will kick-on again and again. As a consequence, over-sized systems run for too short a time far too often. And it can cost you far too much.

An undersized system, however, will not effectively cool your entire home. It will run continuously, waste energy, and wind up costing you more.

Understanding Size: What Do TON and SEER mean?

Air conditioner sizes are rated in ?tons? of cooling capacity. One ton of cooling is equal to 12,000 BTU's (British thermal units) per hour. For example, a typical residential unit is a 2-ton unit that cools 24000 BTU/hour and a larger 3-ton unit cools 36000 BTU/hour.

While two air conditioners be the same tonnage, they could be completely different in terms of their energy efficiency or ?Seasonal Energy Efficiency Ratio?(SEER) . Once you have found the right tonnage-size to cool your home, you'll want to look over which ones have the best SEER rating as is practical within your budget. The higher the rating, the less energy it will use - roughly 5% less per SEER. So an older 12 SEER upgraded to a higher efficiency SEER 16 will be approximately 20% more efficient and will cost less to run. Systems that are Energy Star qualified range between 12 and 23 SEER.

Because air conditioning is one of the most expensive conveniences you can have in your home, it's important to be able to rely on a trained professional that you can trust to listen to your needs and guide you through this complex process. Direct Energy's central AC sizing experts have years of design and installation experience. They'll inform you about the different cooling options for your home and design the right-sized energy efficient cooling system to work with your home's heating system and help save you money.