What Size Air Conditioner Do I Need For My Home?

CHOOSING THE RIGHT SIZED AIR CONDITIONER FOR YOUR HOME.

Choosing the right sized air conditioner for your home is more than just installing one like your old system. There are many factors to consider, including whether or not your old system was right for your home in the first place. There are many other factors about your cooling needs that can directly affect the performance, efficiency, and the energy usage of your air conditioning system. In addition to your own needs and cooling preferences, there are several varieties of central air conditioning systems; different brands, efficiency ratings, sizes, and even installation requirements that you must consider.

In order to make an educated decision on the type of new air conditioning system you need for your home, you will need the aid of an experience HVAC technician, and understand the cooling cycle an air conditioning goes through. Completing an air conditioning cycle is an important factor in the efficiency and the accurate sizing of a unit in your home.

Cooling Cycle and How Air Conditioners Work

Your air conditioner is a part of a whole HVAC (Heating, Ventilation, Air Conditioning) system. Generally, a central air conditioning system is comprised of two parts: an outdoor unit (where the compressor and condenser coil are located) and an indoor unit that is mounted above your furnace heater (where the expansion valve and evaporator coil are housed).

Air conditioning happens when a refrigerant (or “coolant”) is cycled from a gas to a liquid and back again through the use of pressure. The refrigerant begins this cycle as a low-temperature, low-pressurized gas; when you’re a/c is turned on, it is compressed into a high-temperature, high-pressurized gas in the outdoor unit. It then moves into the condenser coil where the gas is cooled to a liquid but remains in a high-pressurized state.

Next it is sent indoors and passes through the expansion valve to the evaporator coil. The expansion valve controls the flow of the liquid into evaporator coil. The liquid refrigerant is able to expand inside of the evaporator coil as the pressure on it lessens and converts back to a gas. The evaporator coil then cools the gas to 7 degrees Celsius (44.6 degrees Fahrenheit). Once the transformation is complete, the gas refrigerant is then returned back to the outside unit where it begins the cycle over again.

At the same time, air taken in through intake vents around your home, and passed through air filters. It is blown over the evaporator coil as the coil is cooling the gas. Any humidity in the air is condensed to water as it passes over the coils and drips into a condensation pan. This is how the air in your home is cooled (and dehumidified). Once it is cooled over the coils, the air is circulated through vents in your home. This is called a cooling cycle.

The cooling cycle is repeated until the desired temperature is reached. Once the thermostat informs your system that the temperature in the home matches the temperature set, the air conditioner ceases further cycles and goes dormant until the temperature in the home raises.

It is important that your air conditioner is able to accurately complete a cooling cycle – and the size of the unit installed for your home will dictate if the system is able to do so.

Why The Size of Your Air Conditioner Matters

A correctly sized air conditioning unit will run a full cooling cycle, which will also keep your home cooled for longer.

An air conditioner that is too large will cool the air in your home quickly, but will shut off too soon (before a proper full cooling cycle is completed). Although being cooler, sooner may seem like a better idea, the building structure (e.g. walls or roof) of your home has not been adequately cooled and will allow the heat and humidity from outside to creep back in at a quicker rate (heat transfers to cooler areas). This will cause your system to continuously turn on over and over again to fight back against the heat constantly creeping in. The short answer is that over-sized systems will run for too short of a time too often.

An air conditioner that is too small will continuously run through cooling cycles in an attempt to reach the desired temperature but won’t be able to get the home cool enough to stop running. Your too small air conditioner will always be running inefficiently, raising your energy usage and your bill.

There are several factors that are considered by an HVAC technician when calculating the right size unit for your home such as:

  • The square footage of the home
  • The area of sun-exposed walls
  • The type and location of your windows
  • The age of your home
  • The amount of insulation (in the attic, around doors and windows)
  • Amount of shade provided by trees or shrubbery
  • Whether or not the ductwork is the right size and properly installed

Understanding TON and SEER Measurements on Your Air Conditioning Unit

The factors labeled above will help the HVAC technician determine the size of air conditioner you need, which is measured in TONs. The A/C measurement of TONs is a unit that measures the cooling capacity of the system. Another way to measure this is in BTUs. One TON of cooling is equal to 12,000 BTUs, or British Thermal Units per hour. So, if you select a 2-TON air conditioner, it is able to cool 36,000 BTUs per hour.

SEER on the other hand is the energy efficiency rating of a system; each system is given a rating between 12 and 23. Air conditioners of the same size, or tonnage, can have different SEER ratings a piece. The higher the rating, the more energy efficient; up to 5% more efficient per SEER. The State of Florida mandates that all air conditioners installed after 2015 be a 14 SEER or better.

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