Check Insulation Levels
Heat loss through your home's ceiling and walls could be large if the insulation levels are less than the recommended minimum. Check to see if the level of the attic and wall insulation of your home is at least at the minimum recommended amount. When your house was built, the insulation levels were probably within recommended standards for the time. Given today's energy prices, and that future prices will probably be higher, the level might be inadequate, especially if you have an older home.
If the attic hatch is located above a conditioned space, check to see if it is at least as heavily insulated as the attic, has weather-stripping to stop air leaks, and closes tightly.
Checking a wall's insulation level can be tricky. One way of seeing what's in your walls is to peek into them by removing the faceplate from an electrical socket. Select an exterior wall and turn off the circuit breaker or unscrew the fuse for any outlets in the wall. Be sure to test the outlets by plugging in a portable radio or lamp to make certain that they are not "hot". Remove the cover plate from one of the outlets and gently probe into the wall with a stick or screwdriver. A crochet hook works particularly well because with its hook it can snag a sample of the material in the wall. If you encounter a slight resistance, you have some insulation there. Outside of looking into the walls through existing openings, you could also make a small hole in a closet, behind a couch, or in some other unobtrusive place to see what, if anything, is in the wall cavity. Ideally, the wall cavity should be totally filled with some form of insulation material.
For unheated basements, determine if there is insulation under the flooring of the living area. In most areas of the country, R-25 is the recommended minimum level of insulation. The insulation at the top of the foundation wall and first floor perimeter should have an R-Value of 19 or greater. For heated basements, the foundation walls should be insulated to at least R-19