If your home is not properly insulated then it will increase your heating cost. Attics and basement are areas where air leaks are commonly found. Sealing and insulating the cooling ducts properly can avoid the leaks and make your heating system more efficient. If you are concerned about reducing your electricity bill then sealing the attic and basement will help you reduce your energy bill. These areas not only drain out warm air but will also let in cool air. A HVAC professional will help you fix the leak by providing proper insulation. Leaks can also happen through the ducts. If the ducts are not properly connected or are damaged the air passing through the duct will leak hence will take longer for the room to heat. Under such circumstance even if you set the thermostat at a very high temperature it will take longer for the room to heat up which would increase your utility bill.
The duct works that are sealed behind the walls or floor will be hard to repair while it is easy to repair those ducts that are exposed. Some of the leaks that are accessible to you can be easily repaired by yourself. Where ever you detect a leak in the ducts seal it using a sealant which is easily available in the market. All you have to do is apply it on the area where there is a leak and let it dry for a few hours. If the joints of the ducts are sealed properly, the air will not leak. For better insulation the duct has to be covered with an insulating jacket. Fiberglass insulation is what can seal the ducts tightly.