4 Problems Caused by an Oversized AC Unit

C.E. Larusso
Written by C.E. Larusso
Updated March 19, 2022
An air conditioner compressor installed outside the house
Photo: Christian Delbert / Adobe Stock


  • HVAC contractors can determine the appropriate load calculation.

  • A unit that’s too big drives up your energy bill.

  • It also fails to keep your home consistently comfortable. 

  • An oversized unit will need frequent repair and die sooner.

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Sometimes it’s best to go big or go home. You can never have too many nachos for a party, there’s no such thing as saving too much money for retirement, and wearing oversized hats gets funnier as they get larger. But when it comes to your air conditioner, the opposite is true. An oversized air conditioner doesn’t deliver peace of mind, only a less comfortable house and higher energy bills. 

Read more to find out whether or not your AC unit is the right size, the problems an oversized unit can create, and what you can do about it.

1. Higher Utility Bills

A unit that’s larger than it needs to be will use more energy to run and deliver bigger blows to your wallet. Additionally, they short cycle—turning on for short periods before quickly turning off—straining the system and using more power than an appropriately sized unit would for a regular cycle. 

Measuring the proper air conditioner load calculation for your home should reveal how to heat the space most efficiently (more on this below).

2. A More Humid Home

An air conditioning unit doesn’t just pump refreshing, refrigerated air into your home, it also removes moisture. When an oversized unit blasts cold air throughout the house in short cycles, the evaporator coil doesn’t have time to dehumidify. This is not only a hit to your daily comfort, it can encourage mold growth in your ducts, which endangers your health and requires a costly removal. 

3. Uneven Temperatures 

One of the telltale signs of an oversized AC unit is the appearance of hot and cold spots throughout an otherwise temperate home. A properly sized unit will gradually cool your home at a steady pace by evenly distributing the treated air rather than pushing rapid bursts of cold air through the ducts. 

4. Frequent Problems and a Short Lifespan 

When an AC unit is too large for the space it cools, you’ll have to devote significant amounts of time and attention to the issues common to such an inefficient system. Short cycling quickly overtaxes the unit’s capacity, delivering unnecessary wear and tear to motors, compressors, and other components. Overheating is also common, which could short your circuits and require repair. Most homeowners pay between $170 and $600 for air conditioning repair

How Technicians Can Determine the Right Sized AC Unit for Your Home 

An HVAC pro will perform a load calculation before installing a new unit. The job includes taking the measurements of each room and assessing your home. They’ll consider the following before recommending the right heating and cooling tonnage (or BTU level).

  • Your home’s position and the sun and the shade it receives

  • Your window types

  • Your home’s building materials

  • Your insulation

  • Your local weather patterns 

Making sure your AC unit is operating at the cooling mode appropriate to the conditions of your house ensures that it can deliver optimal comfort and savings. If you notice the symptoms of operating an oversized unit, call a local HVAC service company to take a new load calculation, as the conditions can change over time. 

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