Do Not Buy Oversized Equipment

When it comes to heating and cooling, smaller is better!
Oversize your furnace and it will turn of and on a lot. These things run most efficiently when warm. I know it is counter-intuitive, but sizing them so they will run and run is most efficient, and is also most comfortable. New furnaces pull so much of the energy out of the fuel that they don’t blow very warm air.
Sizing can create huge problems for your A/C. In humid climates one of the big advantages of A/C is they remove humidity. This has dramatic indoor air quality benefits. Reduced humidity reduces the potential for mold problems. To effectively remove humidity lots of air needs to run across the cold coil. An oversized A/C unit cools the air so quickly it doesn’t have time to remove much humidity. By cooling things quickly you have colder indoor surfaces with a high humidity environment. This can actually increase mold risk as the risk of condensation on solid surfaces has been increased.
When replacing equipment it is a good idea to get an energy audit. This process will determine missed insulation and air sealing (Envelope) opportunities, and make sure you don’t oversize your new equipment. By performing improvements to your Envelope at the time of equipment replacement you can often move to smaller equipment.