Seal the gaps around an exterior door in an afternoon and feel the difference the next cold night.
You can usually find a draft by holding a lit candle near the door frame on a windy day and watching the flame lean. Ours leaned hard at the bottom and along the latch side — classic spots where old foam tape has crushed flat and given up.
We peeled off the crumbling strip, cleaned the frame so new adhesive would hold, and ran fresh V-seal weatherstripping along the jambs. A screw-on door sweep closed the gap at the threshold, cut to length with a hacksaw. The door still latches easily; good weatherstripping compresses without fighting you.
The materials come to about $30 and the job takes an afternoon. It is one of the cheapest upgrades in this whole blog, and the payback shows up on the very next heating bill.