What size A/C is the most efficient for my home?

What size system do I need for my home?

It is important that new or replacement air conditioning and heating units are not sized by “Rule of Thumb” or by duplicating the existing equipment capacity when considering a new install. The only accurate way to determine the correct capacity of heating and air conditioning equipment for your home is to have a load calculation performed. There is a specific method to do this calculation known as a Manual J load calculation. This will give the heat gain and heat loss design data for your home or building. These figures can then be used to select the appropriately sized air conditioning or heating system for your home, based on equipment-performance data. Many factors determine the size (capacity) system your home requires.

Some of these are: Square footage being cooled and/or heated, climate zone, desired indoor humidity, number, location, and type of windows, insulation factors in the walls and attics, which direction the home faces, heat producing appliances, and the number of people who will be in the home, to name just a few.

Oversized air conditioning systems will not remove adequate moisture from the indoor air due to short cycling. Also, oversized systems quickly cool the indoor air temperature, but they do not run long enough to remove the humidity. That leaves you feeling stuffy and uncomfortable. Control of your home’s climate is rarely achieved with oversized systems and electricity consumption is higher than with a properly sized system. An oversized furnace is similar to an oversized air conditioning system. The furnace run time is short, creating uncomfortable air stratification and less air filtration. Also, the frequent cycling of the unit on and off can cause undue wear and tear on internal working components. An undersized air conditioning system will not adequately cool your home on the hottest days and an undersized furnace will not adequately heat your house on the coldest days.

[Screenshot of some load calculation data]

A proper load calculation should include measuring the entire building, accounting for doors and windows, # of occupants, insulation, and much more.

What is a load calculation and why is it so important?

A load calculation determines what the proper size system is for your specific home. It factors in a number of criteria used to determine what size components you should include as part of your total comfort system, things like square footage, number of windows, and year-round weather concerns. A load calculation is important so that your system operates at maximum efficiency, with optimum performance. Most homes have systems that are oversized, so you end up paying more than you should to heat and cool your home. Also, systems that are improperly sized tend to cycle too quickly or too slowly, and that can lead to maintenance problems, uneven temperatures, and an inability to control humidity. A properly sized system based on a correct load calculation can help ensure you enjoy long-lasting, reliable comfort whatever the season.

According to a study done by a local utility company (APS) in our area (Mesa, AZ), over 80% of the homes tested were found to be oversized! While you might think bigger must be better…especially in the desert, this can actually be worse than being undersized.

Here is what APS has to say:

If you live in the Phoenix-Metro area of Arizona, you can contact Magic Touch Mechanical at (480) 855-8789 for a free load calculation on your home and a recommendation of the best system to meet your family’s needs. If you are outside of our service area, we recommend checking customer review websites such as AngiesList.com or Kudzu.com to find a quality contractor in your area.