With an Air Conditioning Unit, Bigger is Not Better

By: Brian Schutt  |  July 24, 2015

A Right-Sized Air Conditioning Unit is Essential For Your Home’s Comfort 

It’s important to have an air conditioning unit that’s properly sized for your home. An air conditioner that’s the wrong size can have significant negative impact on your comfort and operating costs.

Over the next week, I will outline some of the primary risks related to the sizing of your air conditioner, and some of the processes that HVAC companies should use to ensure that the right-sized system is installed in your home.

To start the series, I want to dive into the most common misperception about air conditioners:  bigger is better.

Two Risks of a Too Large Air Conditioner

There’s a common belief—perpetuated by intuition and everything else in our society—that bigger must be better. The same holds true in the HVAC industry. Those who regularly get too hot in the summer believe a larger system must be the better solution.

Unfortunately, it’s just not true. Your house was not designed to handle air conditioning systems of all sizes, and too big of a system can cause two major issues.

  1. While a larger capacity unit can cause the thermostat to reach its set temperature more quickly, it will never allow the air to be evenly distributed throughout your home. You’ll get short blasts of cold air more often, instead of a longer consistent cycle. This makes the home less comfortable.
  2. The constant starting and stopping of your unit will reduce the lifespan of your system. Imagine a car that only drives in stop-and-go traffic. Those kinds of miles have significant wear and tear on an engine. It’s the same for an air conditioner. An oversized system will result in less comfort, higher operating costs, and a reduced lifespan of your system. And on top of all that, it will likely cost more than the properly sized system.

Ductwork and Blower Motors Must Be Sized for Air Conditioner Size

The aforementioned issues assume that the ductwork in your home and the blower on your furnace can even accommodate the larger-sized air conditioner.

Ductwork is designed to move a certain volume of air at a certain pressure in order to maintain a comfort level in your home. The industry term for this process is the CFM (cubit feet per minute) of air coming from a given supply vent. A blower fan is designed to move a specific CFM of air, which should have corresponding ducts for that fan size.

Therefore, if your fan and ducts are designed to move two tons of air—equaling 800 CFM—a 3-ton air conditioner will not allow sufficient airflow through the evaporator coils of the AC unit to cool the home.

As you can see, whichever direction you go, oversizing your air conditioner will cause negative impacts on your comfort, be more expensive to operate, and lead to repairs that a correctly sized system would not likely require.

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