3 Tips to Pick the Correct Size AC System

AC system

If you’re upgrading your central air conditioning (AC) unit this year, ensure that you purchase the correct size of AC system for your home. Here are three things every AC system buyer should know before shopping for AC replacement.

1. Tons or British Thermal Units Are Ratings for AC Units

When you shop for central AC systems for your home, you’ll see the measurement term ton in the product descriptions for central AC appliances. An AC unit’s tonnage describes its heat-extracting capabilities. Each ton rating is equivalent to freezing (at 32 degrees Fahrenheit) one ton of ice for an entire 24-hour period.

One ton of refrigeration (TR or RT) is equal to 12,000 BTU/h. BTU stands for British thermal unit. The definition of one BTU is the amount of heat necessary to increase (or reduce) by one degree Fahrenheit the temperature of one pound of water.

The larger the tonnage or BTU rating on a central AC system, the more capacity the AC unit has to cool indoor spaces. To find the right BTU rating for your residence, you must calculate the optimum BTU rating for the total square footage amount you wish to cool.

2. Room Measurements Determine Ideal AC Sizing

Your AC professional can help you calculate the best size of central air conditioner for your home. If you want to do the math yourself, first measure the total width and length of all rooms you wish to cool.

For example, when your home consists of two 12-foot by 10-foot bedrooms, one 6-foot by 8-foot bathroom, and one combined kitchen/dining/living room that measures 18 feet by 12 feet, your rooms’ total square footage equals the following:

  • Bedrooms: 12 feet X 10 feet X 2 rooms = 120 square feet
  • Bathroom: 6 feet X 8 feet = 48 square feet
  • Dining/living room/kitchen: 18 feet X 12 feet = 216 feet

TOTAL square footage in the above example: 120 square feet + 48 square feet + 216 square feet = 384 square feet.

Most homes have hallways, closets, and other spaces that must be cooled, so calculate the total home square footage for a whole-house central air conditioning unit. If you choose a split or mini-split AC system, simply add together the total square footage of the individual rooms where the units will be mounted.

After you determine the total square footage you want to cool in your home, multiply the total square footage by 25 BTU. In the above home, 384 square feet multiplied by 25 equals a required central AC unit with at least 9,600 BTU capacity.

3. Oversized and Undersized Central AC Units Cause Problems

Many homeowners believe that the size of a central AC system doesn’t necessarily have to match the size of the home being cooled. However, the size of your central AC unit is key to home cooling performance, humidity reduction, and cooling costs during summer.

While an undersized AC system may be less expensive to install than a larger unit, the long-term costs of an undersized central AC system outweigh any initial savings. Undersized AC units must run longer to keep up with the cooling load in a home that’s too spacious for the unit to handle normally.

A central AC unit that runs continuously will increase your power bill during the summer months. The undersized central AC unit will have a hard time keeping up with your cooling needs on extra hot and humid days.

Oversized central AC units won’t cool a home better than a correctly sized AC unit, even if the AC system is rated at a higher BTU level. However, an oversized unit only needs to run for a few minutes to cool your home, which means the AC system will cycle on and off more frequently.

Constant cycling on and off adds wear and tear on the AC unit, which means the appliance will probably not live up to its useful life expectancy. An oversized central AC system may need repairs and replacement more often than a central AC system that is sized correctly.

Oversized AC systems are also notoriously bad at removing humidity from the air. Because the fan and compressor only run for short periods in an oversized central AC system, the AC unit doesn’t operate long enough for moisture in the air to condense and fall into the drip pan of the AC unit.

Humidity in the air continues to cycle through your central AC system and your home when you have an oversized central AC unit. The moisture can lead to mold and mildew problems throughout your home.

Purchase a properly sized central AC appliance to get the most value, performance, and efficiency out of your AC system. Contact Derek Sawyer’s Heating & Air Conditioning today to learn more about the energy-efficient modern AC appliances available today. We install, repair, and service AC systems for residential customers in Fresno, Modesto, Chico, Stockton, and Sacramento, California.

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