Energy Coach Corner: Air Conditioners – Don’t Super-Size It

Written by: Lauren Brois on Jul 1st 2014
Energy Coach Corner: Air Conditioners – Don’t Super-Size It

The other day, I was in a store looking at room air conditioners.  A couple standing next to were also looking at air conditioners.  They had done some research and based on the size of the room they wanted to cool, they were told they needed an air conditioner rated at 6,000 BTU.  Instead, they chose an 8,500 BTU model.  Their reason?  Simple:  bigger is better.  When it comes to air conditioners, there are a few really good reasons why an oversized air conditioner is a poor choice. 

To understand these reasons, first it is important to understand why air conditioners are such amazing devices.  Air conditioners do not one, but three different things to make us feel more comfortable during the summer:

Cooling – Of course, we know air conditioners reduce room temperatures.  However, they do more:

Dehumidification – As warm moist room air is cooled inside our air conditioners, condensation occurs (this is why we see water dripping from our air conditioners when they run).  Therefore, air conditioners are powerful dehumidifiers.
Air movement – During the summer time, air movement accelerates the evaporation of moisture from our skin, helping our bodies stay cool.  Air conditioners keep air moving within a room.

When an air conditioner is running, it makes us comfortable because it cools, dehumidifies, and moves air all at the same time.  When it is not running, well, it does none of the above.

Now then, back to the couple who bought the bigger AC  I am predicting that the couple will find that their new air conditioner will very quickly cool a room because it is much larger than necessary.  Once the room temperature falls, however, the air conditioner will turn off.  Because the air conditioner is so powerful, each time it turns on, it will run for a short period of time, then turn back off.  Without the air conditioner running, the room does not benefit from dehumidification or air movement.  The result is a cold “clammy” feeling in the room.  Hardly comfortable!  A properly sized air conditioner runs almost constantly on a really hot day.  The benefit is the cooling accompanied by plenty of dehumidification and air movement.

Another reason why oversized air conditioners are a poor choice is their impact on our utility bills.  Some of us may have noticed the lights in a house dim when an air conditioner turns on (especially common in older homes with central air conditioners).  This illustrates the point that air conditioners typically draw much of their power getting started.  Oversized air conditioners draw more power to start than smaller ones.  To make matters worse, they start and stop more frequently (short cycling), drawing even more power.  The result:  it costs more to operate an oversized air conditioner.

Whether picking out a simple window air conditioner or a central air conditioning system, it is important to pick a unit that is properly sized.  Let’s leave “super-sizing” to the folks at McDonalds.

- Norm Jen, Energize NY Energy Coach

As a service to homeowners in Northern Westchester, the Energize NY Energy Coach is available to meet with you, after your home energy assessment. Norm is a third party, independent contractor who can help you understand your home energy assessment report. To schedule an assessment call the Energize NY Office at 914-302-7300 or email