The first step to making a dent in your heating bill is to button up areas of the house that let heated air out like the seal around doors and windows. Filling the gaps around the movable joints on the inside of doors and windows with weatherstripping will stop air penetration and lower heating costs.
If you walk around the outside of your house inspecting the joint around doors and windows you may find gaps where cold air seeps inside. Use a good quality 100% silicone caulk to fill the gaps and you’ll plug the leaks from getting inside, another way to button up your house.
There’s a mind-numbing array of sealing materials to choose from at hardware stores and home centers. Choose those that are designed for doors and windows and its ease of installation.