I used to believe that the bigger the air conditioning and heating system the better. I figured that more power would translate into superior comfort and lower monthly costs. Assuming a large heating and cooling system would heat up or cool down the home more quickly, I started doing some research into different models. I discovered that an oversized furnace and air conditioner would result in higher energy bills, less indoor comfort, and problems with operation. It’s not as simple as buying the biggest or most expensive heating and cooling system. Even calculating the square footage of the house isn’t enough to properly size temperature control equipment. The HVAC contractor who is hired to install the new system needs to consider issues such as load estimate, maximum occupancy, SEER ratings, and AFUE ratings. The heating and cooling system must be designed to suit the home’s specific thermal envelope. The thermal envelope encompasses the barriers to the outside, such as the walls, insulation, roof, windows, doors and foundation. A correctly sized and installed HVAC system can be expected to last approximately fifteen years. It will maintain even comfort, despite the weather outside, and operate efficiently and reliably. An oversized system will heat or cool the home too quickly. The compressor and fan then turns off until the next cycle, which happens within minutes. The constant on and off of the equipment is called short cycling, and it wear out components and limits air circulation throughout the home. This negatively impacts indoor air quality and the health of the home. Since the system is continuously shutting off and turning on, it’s also drawing more energy and causing higher utility bills.