You may already know about the draft that comes in underneath your front door (a new Therma-Tru door would solve that problem!) but there may be hidden air leaks that aren’t as obvious which could be costing you more money on energy bills.
Here are some suggestions from energy.gov: On the outside of your house, inspect all areas where two different building materials meet, including:
Inside your home, inspect around the following areas for any cracks and gaps that could cause air leaks:
Also look for gaps around pipes and wires, foundation seals, and mail slots. Check to see if the caulking and weather stripping are applied properly, leaving no gaps or cracks, and are in good condition. Check the exterior caulking around doors and windows, and see whether exterior storm doors and primary doors seal tightly.