Do you have a fold-down attic stair in your house? Is the stair insulated? Most attic stairs are not insulated, or have a crushed piece of fiberglass stuffed under the treads in a half-hearted effort to impress the inspector.
Even small gaps in ceiling insulation cause major reductions in energy efficiency.
What about those huge insulation gaps at the attic stair? I haven't even mentioned the poor contact of the stair with the ceiling when the stair is closed.
Is your stair weatherstripped? Well, here's an elegant solution that my brother-in-law built for my parents:  a box built of foam board sheathing, two inches thick, held together with wood dowels and glue, very lightweight.
It is about eight inches high to allow the stair springs to fit under it when the stair is closed.
Any handy person could build one.
  Foam weatherstripping around the perimeter seals any gaps, and it just sits on the attic floor over the stair when the stair is closed:  When you open this door, nothing falls on you - no dust, no glass fiber.
And the heat pump runs less often.
If you have an access panel rather than a stair, you can just glue several layers of  foam board to the top of the panel.
  Instant energy savings! What you need to build it:

• One piece of 2 inch thick foam board insulating sheathing (available at most large home supply stores)
• 1/2" wood dowel stock
• Foam board compatible glue (comes in a caulk tube)
• Soft foam adhesive weatherstripping
• Tools: sharp knife, drill and 1/2" bit, caulk gun, measuring tape or yard stick

Click here to see photos of the insulation box.
Directions: Measure the opening in the attic floor - you want the inside of the box to be about an inch bigger than this opening.
  Close the stair (have a helper you really trust for this step) and measure the height of the stair above the attic floor.
  Allow an extra inch for the interior height of the box.
Cut the main top panel four inches bigger than the inside measurement you made.
Cut the side pieces to the height you measured with the stair closed.
  For the cuts use a sharp knife and a straight edge, or cut the foam board on a table saw if you have one.
  Assemble the pieces by drilling holes at the edges and corners and inserting dowels, and glue it all together.
  Let the glue set up overnight and then adhere the weatherstripping around the base of the box.
   Install your new insulation and pull out the old dirty insulation from the attic stair.
Enjoy your energy savings!