Do You Have an Oversized or Undersized AC? How to Tell and Why It Matters

Accurate sizing is essential to long-term air conditioning performance. The cooling output of your AC not only affects comfort but also energy efficiency, day-to-day expenses, and long-term costs. Let’s explore how to tell if your AC is oversized or undersized, along with the consequences and potential solutions.

The Signs You Have an Oversized or Undersized AC

A central AC will typically cycle for 10 to 15 minutes, while an undersized AC may run for 20 or more. You may notice the extended cycling even more during late afternoon or when there’s significant sunlight. It’s not uncommon to experience a warmer upstairs or warm spots throughout the ground floor. Undersized units also tend not to dehumidify as well. That can result in the home feeling muggy despite being relatively cool.

A well-functioning AC will cycle on two to three times an hour. An oversized unit will turn on more frequently, which the industry calls short cycling. Frequent cycling can also result in uneven cooling and high humidity levels. That’s because the system never runs long enough to provide the airflow and dehumidification required. As the problem worsens, you can experience excessive noise, large temperature swings, frozen evaporator coils, and even overheating.

How AC Oversizing and Undersizing Happens

Accurate sizing is a key reason professional AC installation by a trusted, experienced installer is so important. Oversizing and undersizing are common with do-it-yourself installations because homeowners use cooling output estimates rather than precise load calculations. Inexperienced and disreputable HVAC contractors may also perform incorrect calculations.

Incorrect sizing can occur when homeowners continue to use outdated and/or deteriorated ductwork. Ducts have a maximum lifespan of roughly 25 years, but the ducts are much older in the average U.S. home. Untrustworthy companies may push larger systems because there’s a higher markup and more profit for them. The previous homeowner could have pushed for a smaller unit in order to save money prior to selling the house. Likewise, some homeowners think bigger is better, which isn’t necessarily the case with AC. Another common issue is home addition projects that don’t account for the HVAC system. Those add-ons increase the cubic footage and impact the building envelope.

The Consequences of Having an Oversized or Undersized AC

Accurate AC sizing is important for consumers because it minimizes short- and long-term costs. An oversized or undersized AC will use more energy than necessary and thus cost more to run. Another problem is that they experience significantly more wear and tear. That will increase your total costs through more frequent repairs and shorter equipment lifespans. An improperly sized AC and/or ductwork typically voids the manufacturer’s warranty as well.

Of course, an oversized or undersized AC will also have a dramatic effect on your comfort. Achieving and maintaining your ideal temperature will be more difficult and perhaps impossible. Both frequent and extended cycling can have a negative impact on your air quality. That includes airborne particulate matter but also high humidity levels. Beyond 60% relative humidity, you are much more prone to respiratory inflammation, mold, and dust mites.

What You Can Do to Rectify the Situation

The most straightforward option, but also the most expensive, at least in the short term, is a full replacement. An installer can remove the existing equipment and replace it with a properly sized system. If the problem is duct-related, your HVAC company can design and install an appropriate duct network. With both oversized and undersized AC units, it may be possible to adjust or replace the blower. That would allow the system to achieve the necessary static pressure. In the case of an undersized AC, you may be able to augment it with a mini-split AC. Other options that may partially or fully solve the problem include:

• Duct sealing
• Air sealing the home
• Zone control integration
• Adding a whole-house dehumidifier
• Installing a thermostat with remote sensors

Custom AC Sizing Solutions in Chesapeake and the Surrounding Areas

For over 50 years, Simmons Heating & Cooling has been a local AC company serving Chesapeake, VA. Our NATE-certified HVAC technicians can perform a custom load calculation to determine your home’s ideal cooling output. We can also help you with lasting solutions, including full replacements, mini-split add-ons, and other upgrades. To schedule an in-home consultation, call today or book your appointment online.