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For whatever reason, the old front door of my house has always been a huge headache air sealing. The door itself is fairly old. Since I purchased the previous occupied home, the door has always had a gap near the upper right hand side. But sealed perfectly fine around the other three corners. In fact, the door is perfectly aligned. The most common fix for stopping drafts around a door is to use foam weather stripping tape around the edge. So I bought a pack for around $10 and taped up top right corner with the gap.
What I didn't realize is that adding the foam probably helped in the short term, but may have worsened the situation in the long run. Because the foam has some thickness, it worked well in areas with the larger gap, but failed miserably in sections of the door with a smaller gap. In fact, the weather stripping was making it difficult to close the door right near the door knob.
The correct solution is to install $4 V-Seal weather stripping. Based on my observations, this type of weather stripping does much less insulating, as it isn't foam, but rather a thin flexible plastic folded in half which can adjust to nearly any width to stop a draft. Not that because this product is so thin, it don't believe it will actually insulate. However, my first goal here is to stop the draft.
Installation is easy as you just remove the tape and adhere to the door jams surface. You want the tip of the V to face the side where the door is closing. It takes no more than 10 minutes to remove the old foam weather stripping and applying the V-Seal weather stripping.
Lastly, I suspect its working now because the entryway is matches within 0.2 degrees when compared to the family room at the other end of the house. I have yet to see how well it performs in the winter season, but I do have high hopes!