Why Size Matters for HVAC

Recently one of our certified contractors met with a customer who wanted a bid on a new furnace and air conditioner. The comfort advisor met with the wife who was prepared with size specifications that her husband had provided. He wanted a 5-ton air conditioner and a 125,000 BTU furnace. Upon inspection of the current system the house had a 2.5-ton air conditioner and a 75,000 BTU furnace. The homeowner’s reasoning was that bigger size must result in more comfort.

Except that it doesn’t. In fact, the National Institute of Standards and Technology (NIST) says that 90% of residential HVAC systems are OVERSIZED.

Why does an oversized system reduce comfort and efficiency?

Comfort. An oversized furnace or air conditioner heats up or cools down the house too quickly. The result is the home is mostly too hot or too cold, and seldom just right. An oversized furnace heats the house so quickly that it overshoots the desired temperature before the thermostat can turn the system off.

Efficiency. Most of the energy consumed by your furnace or air conditioner is consumed when the system cycles on. An oversized system is going to constantly be turning off and on, using much more energy than if it was right-sized and running consistently keeping temperatures even.

The other issue with an oversized system is that the duct system has to be matched to equipment. Trying to force too much air through a small duct system will result in excessive wear and tear on your equipment and it will shorten its life.