Should I Upsize or Downsize the AC Unit in My Yuba City Home?

Our city of Yuba boasts amazing family events, like the recent Yuba-Sutter Fair, that keep first-time homebuyers seeking their dream homes right here in Sutter County. But with the joy of finding that perfect house comes the added costs associated with becoming a homeowner.

As a new homeowner, you’ll have to handle home repairs—possibly for the first time in your life. Many people embrace the challenge of replacing door hinges or caulking windows, but some home repairs, such as updating your HVAC system, require the expertise of professionals. If you are replacing your AC unit, you might assume you should buy the same-sized unit as the old one—but this is only the case if the unit was already sized correctly. And figuring that out will require a little good, old-fashioned math, whether you just bought your first house, or your tenth.

Factoring in the Size of Your Air Conditioner

The size of your AC unit isn’t necessarily determined by the size of your home—this is a common misconception amongst homeowners and builders alike. Whether you are building a new home, buying an older home, or just doing general maintenance, it’s important to understand that sizing your air conditioner requires looking at the entire layout of your house and considering many different factors.

The Manual J load calculation crunches the numbers on all the factors that affect the heat gains and losses of a building, or why and where your home is letting energy, such as heat and cool air, escape or enter. These factors include:

• Square footage: Often call the “Rule of Thumb,” and the only calculation that some contractors use to determine air conditioner size, square footage is a good baseline number to start with, but it doesn’t take into account any of the additional contributing factors listed below.
• Climate Zone: Yuba City is in California Climate Zone 11. Understanding your climate zone is important to cooling and heating your home as the daily weather your home has to combat has a big impact on its energy use.
• Orientation of Your Home: Orientation is your house’s position in relation to the sun. This is important because if your windows are all facing south, for instance, and receiving maximum sunlight during the day, this can add up to large heat gains in your home versus a house with northerly-facing windows.
• Walls, Ceilings, and Floors: How well the walls, ceilings, and floors of your home are insulated against heat gains and losses is a huge factor when determining which AC unit to buy. Insulation R-values are a helpful tool in measuring heat flow and loss.
• Windows, Glass Doors, and Skylights: Windows and glass doors have U-ratings and solar heat gain coefficients (SHGC) that can help you determine how much heat is kept out—and how much is gained. The ratio of glass windows and doors to the exterior of your house should also be taken into account.
• Internal Heat Contributors: You and your family help to heat up your home—the more people in a space, the more heat they put off. This is especially true when you factor in our use of modern appliances such as ovens, dryers, computers, and other electrical equipment.

Why Calculating the Right Size for Your AC Unit Matters

Why am I so adamant about taking a long, hard look at the size of your AC unit? Because a poorly-sized unit ultimately costs you money. Issues that result from under or oversized units are:

• Excessive use of energy: An undersized unit may never stop running because it is not designed to meet the heating loads on your home. It’s the equivalent of pouring a teaspoon of water onto a forest fire.
• Unnecessary repairs: An undersized unit that is constantly trying to heat up or cool off too large of an area will become overworked; and an oversized unit may continuously cycle on and off. Both cause unnecessary wear and tear on the fan motor, meaning worn out equipment that requires avoidable repairs.
• High humidity in the home: While this is not typically an issue for Yuba City, in those rare heat waves where we have a build-up of moist air, it isn’t pleasant. An oversized unit doesn’t create enough condensate to drain to the outside of your house. That means if you leave the fan of your AC on, instead of putting it on auto, all that moisture will go back into the air of your home.

If you are ready to get the facts on your home’s heating and cooling loads, you can find many different DIY load calculators online. But, if you want accurate results, consult an HVAC professional who can look at every piece of your home’s HVAC puzzle. Having an HVAC professional perform the Manual J load calculations for you as part of their installation service is a simple process that could save you a lot of money in the long run.

When it’s time to update your HVAC, or if you are concerned you’re losing energy and money from a wrongly-sized AC unit, give the professionals at Bell Brothers a call today. We’ll be happy to do the math for you.