Question: My house has an old wood front door and a steel back door. I don't want the expense of replacing them, but I want to make them more airtight and efficient. What can I do to improve them?
Answer: Doors can be significant areas of energy loss in a home. Many homes have a front door, a back door and a door from an attached garage. When you total up the perimeter length of the doors, you can see how much potential there is for costly air leaks if the weather stripping doesn’t seal properly.
Before attempting any improvements, carefully inspect each door, especially the wood front door. If the wood is deteriorated or warped, there really is not much you can do but replace it. Although they are more expensive, I generally recommend steel or fiberglass doors as they last longer and seldom warp.
You mentioned making the doors more airtight, so I assume you can feel air leaking around them. On a windy day, hold a stick of lighted incense near the weather stripping and move it around the door perimeter. The trail of smoke will indicate the location and size of any leaks.
Push on the door with your hand to force it to close tighter against the weather stripping and then check with the incense again. If you are lucky, the only problem is that the door not closing tightly enough to create a good seal. This is most commonly the result of a worn striker plate on the latch side of the door. The easiest solution to this problem is to remove the old striker plate in the door frame and install an adjustable one.
If the doors are old, you would be wise to replace the threshold seal, and perhaps the entire threshold plate under the door. Most newer doors have a weather stripping seal attached to the door bottom, but with some older ones the seal is attached to the floor itself where it can get damaged and crushed by years of foot traffic.
If you choose to install a new threshold seal underneath the door, you will have to remove the door from the hinges. The new seal will likely be thicker, so you will have to saw a thin strip off the door bottom for clearance. This is fine for a wood or fiberglass door, but you will not be able to do this on a steel door. For a steel door, consider installing an automatic door bottom seal which moves down to touch the threshold just as the door closes.
Finally, check the hinges. Worn hinges can also cause sealing problems if they allow the door to hang crooked. Most home center stores carry an array of hinge sizes which fit almost any door.
At this link you will find more energy upgrades that save.