Air Conditioner Sizing


Air Conditioner Sizing Problems & Solutions

What Size Air Conditioner Do I Need For My House? This is the most common question asked by homeowners.

Most air conditioner sizing is done incorrectly. A study done by CEE “Consortium of Energy Efficiency” says not all air conditioners are properly sized and installed. The improper air conditioner sizing and installation done by contractors have shown a 47% data and keeps increasing. Other studies showed the following major problems with improper sizing and installation.

  • Incorrect air conditioner sizing causes improper air flow 70%
  • Improper refrigerant charge causes less efficiency 44%

Common Air Conditioner Sizing Mistakes


Central Air Conditioner Sizing

Research has shown that the most common sizing mistakes are:

  • Miscalculation of the home’s square footage and orientation
  • Also Miscalculation of Air changes per Hour (ACH)
  • Exaggeration of outdoor temperatures (too warm for cooling equipment sizing)
  • Sizing by capacity of existing equipment (which often is wrong)

Choosing the right size of Air Conditioner

A lot of contractors eliminate the very important steps to choosing the right size of air conditioner for their customer’s homes. The following steps are usually dismissed.

  • A proper load calculations
  • Inspection of the existing duct work
  • Appropriate component matching

These are key steps for contractors to help with their customer’s options. A load calculation properly determines the amount of proper size of furnace and/or air conditioner for your home. The existing exposed duct work should be inspected and if required be sealed. Don’t forget the condensing unit should be matched with proper evaporator coil to reach maximum efficiency based on AHRI guidelines.

Problems from Over-sizing an Air Conditioner

Over-sizing an air conditioner can cause serious problems for the home owner and ultimately a costly mistake. Over-sizing can lead to:

  • Higher equipment cost
  • Excessive loading and unloading
  • High humidity level in conditioned space
  • Occupant discomfort
  • Short and frequent cycling which kills the compressor in less time
  • Large conditioned space temperature swings (feeling hot or too cold)
  • Shorter equipment life
  • Nuisance service calls
  • Low efficiency and high operating costs

Six Major Factors in Air Conditioner Sizing Impact Comfort & Efficiency

  1. Proper duct design and sealing exposed leaking ducts.
  2. Size of system.
  3. Coil matched with condensing unit.
  4. Adequate air flow over the indoor coil.
  5. Adjust refrigerant charge when unit is installed.
  6. Complete commissioning and refrigerant check based on manufacturer’s installation guide.

Rule of Thumb

The rule of thumb is for every 1,000 square footage of space you require a ton of cooling. However this being said, there are more factors that should be kept in mind when sizing air conditioners. A proper calculation of your home’s heating and cooling needs based on number of factors. These include the type and number of windows. The amount of insulation and construction of the home.

Be sceptical of proposals that simply replace the existing unit. Be sure to ask lots of questions and know what to expect when choosing the right size of air conditioner for your home.

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