What Size Ductless AC Do I Need?

Ductless air conditioning systems have become increasingly popular in recent years. That’s not surprising!

Versatile and Efficient

A ductless system provides the ability to cool isolated interior spaces like a garage or spare room  because of two key innovations:

  1. They require no ducting to circulate air from a central air handler, so there is no need for expensive remodels to install or extend additional ducting.
  2. Unlike a standard room air conditioner, they do not require a window to vent to the outside.

They are also efficient and have the capacity to reduce energy costs. Ductless systems deliver coolant directly to an interior room’s evaporator/blower through refrigerant lines connected to an exterior compressor that also houses the condenser and coil.

These innovations offer distinct benefits to homeowners. The versatility and efficiency they provide are pushing ductless systems to the forefront of the air conditioning industry.

Sizing Your Ductless System

There are several things to consider when determining the size required for your system. First is a knowledge of how air conditioners work.

Understanding Cooling

All air conditioners use the same principles to cool air:

  • Refrigerant is compressed and pumped through refrigerant lines by a compressor
  • The refrigerant circulates through a cooling coil/evaporator that cools indoor air, removing heat and moisture
  • A blower sends the cooled air through the house
  • A condenser and fan located with the compressor outside dissipates the heat transferred from the indoor air to the refrigerant
  • The cooled refrigerant is pumped back inside to repeat the cycle

Calculating Size

Another concept to understand is the term BTU (British Thermal Unit). A BTU is the amount of energy needed to raise the temperature of one pound of water by one degree Fahrenheit at sea level.

In air conditioning, the BTUs represent the amount of heat removed from the air per hour by the unit. A half ton air conditioning unit removes 6,000 BTUs per hour. A one-ton unit removes 12,000 BTUs, and so on.

Here is a simplified example of BTUs and ton requirements:

Square Footage


AC Unit Ton


5,000 – 6,000



8,000 – 9,000



11,000 – 12, 000



21,000 – 24,000


Keep in mind that these are approximate size requirements for illustration. Calculating BTUs for your specific needs will vary depending on factors other than square footage, such as:

  • Number of rooms to be cooled
  • Number of windows in each room
  • Size of windows
  • Height of ceilings
  • Type of home insulation
  • Climate zone and seasonal temperatures

It is important to size your ductless AC correctly. An undersized system will result in inefficient cooling. An oversized one will cause the units to cycle on and off frequently resulting in higher energy consumption.

Call All Seasons for Help Sizing a New Ductless Air Conditioner

The expert team at All Seasons Heating and Cooling can ensure that your ductless air conditioning system is correctly sized and installed to meet your needs. Give us a call today at (443) 304-2379 or contact us online!

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