Heating and Cooling account for 50 to 70% of the energy used in an average home with inadequate insulation being the major cause of energy waste, but how do you know how much insulation you need, where it should go, or what type is best? The answer is very depending on a number of things, like where you live, the size of your home, how old it is, etc.
This chart from the Department of Energy gives general guidelines on the right amount of insulation based on geographical zones and a rating called R-value. R-value measures the resistance of heat flow through the insulation so simply, put the higher the R-value the better the insulation.
Now every piece of insulation contains a label clearly indicating its R-value as to where insulation should be placed in your home. This illustration from the Department of Energy's website provides a good overview of key areas in the home increasing insulation, where you already have some like an attic is a good start, adding fiberglass batts or loose fill cellulose is a quick and easy project. That will provide immediate payback in energy savings.
Two more things to think about when you're adding insulation. First check to make sure that the insulation that you already have is faced, what that means, is that it contains moisture or vapor barrier. Now when you're adding insulation to that you need to make sure that the new insulation is unphased, it does not have the vapor barrier because you don't need to vapor barriers in the attic.
The other thing to think about is if your existing insulation is running north to south, try running the new insulation east to west, that way you really make sure that you cover up any gaps that you might have in the insulation, even more, energy can be saved by insulating places that have never been insulated, such as a wall that separates a room from the attic or an uninsulated floor over a garage.
Adding insulation to exterior walls is a little more difficult, but you've got a couple of options, you can hire a contractor to come in and blow in loose fill insulation or you can rent a blower from a home depot rental center and do it yourself. Wrapping heating and cooling ducts with foil faced fiberglass jackets, another energy saver as is using insulating sleeves for all accessible water pipes, especially any that run through unheated spaces, and simply caulking, and weather. Stripping around windows and doors is one of the easiest and best ways to keep a home airtight.
Invest just a little time and money in making your home more energy, efficient, and you will save a bundle and feel the difference.