Bigger isn’t always better

A larger AC or furnace isn’t always the answer

Posted on Jul 02 2019 in Energy


Bigger must be better! This is a common misconception of many homeowners during the heating and air equipment buying process. Although it may sound attractive to size your system to its largest capacity, from an energy efficiency standpoint it is never a good idea to oversize your furnace or air-conditioning unit.

Have you ever noticed the temperature difference in the air when humidity is high vs. low? If humidity is removed from the air, you feel cooler. This benefits your air-conditioning unit, but not your home’s heating ability. When a furnace is oversized, the air will become excessively dry. Adversely, when an air conditioner is oversized, not enough humidity is removed. In either case, the homeowner will feel uncomfortable and thus increase the thermostat setting. 

HVAC no-nos

Heating, ventilation and air conditioning (HVAC) systems are not designed to be continually adjusted. They could even short cycle if the homeowner is not careful. This could result in excessive wear and tear on motors and starting components. The life expectancy of a system will decrease and the efficiency and operating cost will increase. This cyclical process is similar to fuel efficiency in an automobile when driving in the city vs. driving down the interstate.   

Even though oversized systems will satisfy the temperature setting on a thermostat, an oversized air conditioner that begins to short cycle will not be able to remove humidity from the home. 

Over time, the moisture being left behind will start to become noticeable. In some severe cases, moisture may drip from walls and mildew may develop. Mold could start to grow in the walls and on surfaces. This problem will leave many homeowners confused. The thermostat may have reached the desired temperature but the homeowner may still not be comfortable. 

In the long run

The only way that an air conditioner can remove humidity from a space is by longer run times. When an air conditioner runs longer, it has more time for the indoor coil, or evaporator, to grab moisture out of the air and drain it to the outside. 

Proper sizing of your home’s comfort system is important. When it’s time to install a new heating and air system, whether it’s replacing an existing system or new construction, request that your contractor run a heating and cooling load calculation. Load calculations can be computed easily with software. 

A homeowner should also pay attention to the equipment itself. Always check that the equipment is certified with the Air Conditioning, Heating, and Refrigeration Institute (AHRI). AHRI ensures that manufacturers accurately list ratings of their products and set standards for consumers to compare equipment. Before purchasing a furnace or air conditioner, remember that the proper size is the key to comfort!

ZACH MOTSINGER is the energy advisor at Orange County REMC in Orleans, Indiana.