Is It Hard trying to open and close the front door?
If your door is hard to open and close, it may be time to replace it. When you feel your door sticking in the winter and easy to open and close in the summer, that’s a sure sign of energy rushing out your door. If the hinges are sinking, that’s another issue. But if its sticking into the door jam, your door probably has exposed areas either down the sides or top or bottom where you can see light. Seeing light from the inside or outside without the door being open is a problem. If you take a lighter a couple inches around those edges, pay attention to what the flame does. It will try to move right outside the door. This indicates leaking air.
How many dings and dents does your door have?
Dings and rust on a door shows that the structural reliability of the door may be compromised. Most residential doors off the shelf at a Home Depot or Lowes are laminated 24-26 gauge steel on top of a wood frame. This is not a very fundamentally sound door. These doors barely qualify as a residential door.
Does your front door have moisture between the panes of glass?
Just like new windows, a lot of doors with glass packages have double-pane glass. Over time with older doors, the seal between those two panes will fail leading to moisture, mildew and/or mold between the panes of glass.