What’s the Right-Sized Air Conditioner for Me?

what size air conditioner?

Air Conditioners are sold with different sizes and ratings.  The size of a unit is measured in tons (if you want to read the back story including lots of fun history and math, this article explains). When shopping for the right size air conditioner, it is important to select the correct tonnage for your equipment.  An oversized air conditioner will not work as well as a correctly sized one. 


In addition to the number of tons a unit is, we also measure its SEER rating.  The Seasonal Energy Efficiency Ratio (SEER) is the amount of cooling output divided by the amount of energy input.  The higher the SEER, the more efficient the unit.  Old systems have a SEER of 10 or under.  The most efficient new systems can get to 26 SEER in ideal conditions.  Generally, selecting the SEER rating that reflects your budget and matches the existing ductwork in the home is sufficient, but the tonnage is a different story.  

Why Do People Oversize?

There are a few common reasons that a homeowner may end up with an oversized unit.  One possible culprit is the homeowner themselves.  The home is often too warm, so when the time comes to replace, they request a “larger” unit.  They believe this will provide them with more cooling.  A quality contractor like Climate Heating and Cooling would tell them that they need the right size, not a larger size.  However, many low-quality/low-cost contractors will sell the most expensive unit they can convince you to purchase, even if it isn’t correct for your home.  A quality contractor will run a load calculation on your home and determine the correct amount of cooling needed for your home.  This will prevent the sale of an oversized unit. There are a number of drawbacks to an oversized unit.

Why is Oversized a Problem?

  1. Cost – Larger units cost more.  The initial cost for purchase and installation is higher for a new unit.  The running cost is also higher.  A larger unit has a shorter cooling cycle.  The more energy use for an air conditioner occurs when it is starting up and shutting down.  As this high draw time happens more rapidly, an oversized unit will run more often drawing more power.
  2. Wear and Tear – The time of most wear and tear to the unit also occurs at start up and shut down.  Since an oversized unit goes through more cooling cycles in the day, it will undergo more stress leading to breakdowns.
  3. Uncomfortable – Homes with oversized units can have pockets of cold air and other areas that are not adequately cooled because of the short cooling cycles.  In addition, your air conditioner dehumidifies your home.  It can only dehumidify while it is running.  If your unit only runs for a short cycle, it will not have time to adequately dehumidify your home.  Both of these conditions will lead you to be uncomfortable in your home.
  4. Noise – Larger units are louder.  When not sized correctly for the home, the unit will be excessively noisy while it is running.


If you have questions about sizing air conditioning for your home or if you are looking to replace your air conditioner and are looking for a quality contractor in the DC, Suburban Maryland, Northern Virginia area, please contact us at Climate Heating and Cooling.  We sell and install a complete range of brands.  Ask about financing for installations.

Corey Rodgerson

Corey is a third-generation HVAC technician. Both of his grandfathers started in the trade in its infancy and both of his parents continued the tradition with Climate Heating & Cooling. Corey has earned master's licenses as an HVAC Mechanic, Electrician, Gas Fitter, and Plumber. He has been certified in lead remediation, building performance through BPI, and he has completed five NATE certifications for service and installation of HVAC units. He is committed to training and deploying the best technicians in the industry.

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