If the ductwork in your unheated basement or crawlspace has holes and cracks you can be losing as much as 30% of the heat produced by the furnace. Even at much lower loss rates the extra energy needed to heat your home can cost you an additional $120-$200/year.

What you can do:

If your basement is unheated repair all holes and cracks in your heating ducts that run through your basement.

Once all holes and cracks are repaired add insulation to your ducts.

Caution! If you insulate the heating ducts in an unheated basement be sure to insulate all water pipes in the basement as well. The heat that was being lost from the uninsulated ducts could have been keeping your basement warm enough to prevent your water pipes from freezing. Once the heating ducts are insulated and the heat is no longer escaping into the basement the possibility of pipes freezing will increase.

Savings:

Repairing all cracks and then insulating your heat ducts can save up to $100-$200/year.