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Cooling systems and sizing: What’s right for me?

Posted on July 15, 2014
by Appleby Systems

Air Conditioner sizing Sizing an AC system is primarily influenced by the level of comfort it provides those who occupy its space. Although important, determining an appropriate-sized unit depends on more than comfort alone. Purchasing a cooling system is an investment that needs to account for not only comfort, but also for cooling space - square footage, needs - room or central air conditioning, and your budget. With so many factors to consider, it can be quite the challenge to find an appropriate and suitable AC system to meet these demands.

An important aspect to remember when establishing sizing an AC unit is to take time to form an idea as to what you want your cooling system to do for you. Poor measurements and planning can lead to a mismatch in expectations and reality, and can be seen in oversized and undersized units. AC units that are too large for an area may cool the space quickly, but tend to leave excess moisture in the air, and will produce more short-cycles, leading to higher energy bills. Undersized units - systems that are too small - cannot accommodate sufficient cooling temperatures on account of the space and the unit’s cooling load capacity ratio.

Measurements: sizing up a suitable AC unit

To determine an appropriate size unit, measure the square footage of the areas you want cooled, while leaving out areas you don’t want included (i.e. basement, garage). For square and rectangle rooms, multiply the length of the area by its width. For triangular areas, multiply the length of the area by the width and divide it by 2.

When you have your measurements, contact a certified AC consultant, who can provide you with information regarding your cooling load. The cooling load is measured as the greatest source of heat generating in an area without any cooling system running.

Some general guidelines to keep in mind when measuring:

  • If your room or home is shaded, reduce BTU capacity by 10%.
  • If your room or home receives full sun, increase BTU capacity by 10%.
  • If more than two people occupy the room regularly, add 600 BTU per person.

Other considerations and questions about your system’s cooling load capacity worth reflecting on include:

    • House orientation

    • Space

      • Is it an office building, department, house?
      • Do I need to cool the entire office or house, or just a few rooms?
      • What noteworthy architecture elements (type, size, shape of windows, doors) should I consider when choosing an AC unit?
    • Shading

      • Does the house or office space have natural shading from trees, blinds?

Air Conditioner sizing

  • Number of occupants

    • How many people occupy the space and when is it a high traffic area?
    • Are the rooms with high traffic exposed to a greater amount of direct sunlight?
  • Basement/attic conditions

  • Number of appliances sharing circuit with unit

    • Seek the expertise of a licensed electrician to determine if an additional load can be added to the circuit safely, or whether wiring adjustments need to be made to accommodate your cooling system.
  • Lighting

    • How much natural light does the area receive?
  • Climate

    • How will these warmer months affect my system’s capacity to generate efficient and effective airflow?
  • Insulation

  • Operation costs

    • What type of unit do I need?
    • What are the electrical prices in my area?
    • What activities will I be carrying out in the area (i.e. how many times will doors leading outside be opened and closed)?

The experts at Appleby Systems have helped homeowners like you choose the right unit for 45 years. Call us today and we’ll do the same for you.


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