Efficiency is highly influenced by your ductwork. You might be wondering why that matters. There are really two reasons, and the combination of both issues can make a HUGE difference in your energy bills.

First, because ductwork carries air that is warmer or cooler than the ambient air in your home, and the outside of the ductwork needs to be well insulated to prevent the loss of heat or cooling. In the 70’s and before, most ductwork was what we call “hard” duct. Hard duct is rectangular (or sometimes round) metal duct that is insulated inside or outside. The problem with hard duct is that it has a high heat capacity, which is its ability to hold and retain heat (or cool). If you insulate hard duct internally, it causes more drag on the air, which in turn increases the static pressure (and ultimately lowers efficiency). If you insulate hard duct on the outside, that allows the duct to absorb heat (remember that high heat capacity?), which robs your system of BTU’s of heating or cooling that could otherwise be delivered to the conditioned spaces of your home.

Regardless of where it is insulated, hard duct has a low R-value (a measure of efficiency in insulation), and over time that R-value tends to go down as the insulating materials degrade. So the upshot is that if your ductwork is old, you are spending lots of money conditioning your crawl space, attic, or other area your ductwork traverses. Any poorly sealed duct connections only make the efficiency worse.

Recently built or upgraded homes will primarily have flexible (“flex”) duct that does a much better job of getting the conditioned air to where it needs to go without losing nearly so much energy on the way.