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What size air conditioner do I need for my home?

How to choose the right type and kind.

The basics of how air conditioning works

1. Components

  • A compressor and condenser coil housed in a unit outside your home.
  • An expansion valve and evaporator (also called an "A coil") mounted above the furnace heater inside your home's heating, ventilation and air conditioning (HVAC) system.

2. Process

  • An air conditioner works by cycling refrigerant from gas to liquid and then to gas again through the use of pressure.
  • Refrigerant (known as R-410A) begins the cycle as a low-pressure, low-temperature gas that enters the outside unit where it’s compressed into a high-pressure, high-temperature gas.
  • Next, it enters the condenser coil where the fan cools the gas into a high pressure liquid that flows through tubing 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 into a gas inside the evaporator coil, chilling it 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 is 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. Your home is both cooled and dehumidified by a central air conditioning system.


Choosing the right size unit

Size is a key factor to performance and efficiency of your HVAC system and depends on:

  • Total volume of your home's living space - not just the square footage
  • Area of sun-exposed exterior walls
  • Number, age, condition and orientation of windows
  • Amount of shade from trees and shrubs
  • Amount of sunshine on your home
  • Age of your home
  • Degree of air sealing - amount of insulation
  • Existing ventilation system and ductwork

Why size matters

  • A 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. It will run for too short a time, too often and cost too much.
  • An undersized system will not effectively cool your entire home. It will run continuously, waste energy, and wind up costing you more.

Because air conditioning is one of the most expensive conveniences you can have in your home, it's important to rely on a trained professional to guide you through the process. Enercare’s central AC sizing experts have years of design and installation experience. They'll design the right-sized energy efficient cooling system to work with your home's heating system and help you save money.

Legal notes: Read the fine print.

The contents of this webpage are provided for general informational purposes only. We do not make any warranties about the completeness, reliability or accuracy of the information as it relates to your circumstances. Any action you take upon the information provided is strictly at your own risk. This information is not a substitute for, and is not intended to replace, independent professional advice. It is your responsibility to take all safety precautions and to refer to the product manufacturer's instructions or contact a licensed technician, as appropriate.