If you can feel cold air on your ankles near the front door, or see a sliver of daylight around the edge when it's closed, the weatherstripping has given up. Door seals get crushed thousands of times a year, and after five to ten years most of them are flat, torn or brittle. Replacing them is one of the cheapest energy fixes in the house, and the best time to do it is now, before the furnace starts running every day.
First, Find Out Where the Air Gets In
Don't buy anything until you know what is actually leaking. Do these three checks on a cool, breezy day.
The dollar bill test. Open the door, lay a dollar bill across the jamb so half of it hangs over the weatherstrip, and close the door on it. Now pull the bill out. You should feel real drag. If it slides out with no resistance, the seal is not making contact at that spot. Repeat every 12 inches or so along the latch side, the hinge side and the top.
The light test. At night, turn on the porch light, turn off the lights inside, and look at the door perimeter from the inside. Any glow means a gap.
The hand or incense test. Hold a damp hand, or a stick of incense, along the edges. Moving smoke or a cold spot points right at the leak.
Note what you find. A leak only at the bottom means you need a new door sweep or threshold insert, not a full jamb kit. A leak only near the top corner of the latch side might be a door that has sagged, which no weatherstrip will fix by itself.
Identify the Kind of Weatherstrip You Have
Most exterior doors in American homes use one of these:
- Kerf-in compression strip. Common on prehung steel and fiberglass doors. A foam-filled or vinyl bulb has a thin fin that presses into a narrow slot (the kerf) in the door stop. You can usually see the slot if you pull back the strip at the top corner.
- Adhesive foam tape. Self-stick foam or rubber stuck to the face of the door stop. Common on older wooden doors and storm doors.
- V-strip or tension seal. A folded vinyl or metal strip nailed or stuck into the jamb, which springs open to fill the gap.
- Door sweep or bottom seal. A rubber or vinyl fin attached to the bottom of the door, or a U-shaped insert that slides onto the bottom edge.
Pull out a short section and take it to the hardware store, or snap a photo of the profile. Kerf-in strips come in several fin widths, and matching the original saves a lot of fussing.
What You'll Need
- Replacement weatherstrip kit (a three-piece kit covers both sides and the top of a standard 36 x 80 inch door, roughly $15 to $35)
- Door sweep or bottom seal if needed, about $10 to $25
- Tape measure
- Utility knife or sharp scissors
- Putty knife or stiff plastic scraper
- Rubbing alcohol and a rag
- Hacksaw or tin snips (for metal-backed sweeps)
- Drill/driver and short screws for a new sweep
- A rubber mallet or a block of wood
Step 1: Measure Each Side
Measure the latch side, hinge side and head of the door opening separately, from the floor or threshold to the top inside corner, and across the top between the jambs. Don't assume the sides are the same length; older houses settle, and a quarter inch matters here. Write the three numbers down.
Step 2: Remove the Old Seal
For a kerf-in strip, grab the top end and pull steadily downward. The fin should come out of the slot in one long piece. If it tears, pick out what's left with needle-nose pliers.
For adhesive foam, peel it off and then scrape the residue with a putty knife. Stubborn adhesive comes off more easily if you warm it with a hair dryer for 30 seconds. Finish by wiping the surface with rubbing alcohol so the new adhesive has a clean, dry surface to grab.
For nailed V-strip, pry out the small nails carefully so you don't split the jamb.
Step 3: Cut and Install the Top Piece First
Cut the head piece to length plus about 1/8 inch so it compresses snugly between the side pieces. On a kerf-in strip, start at one corner and press the fin into the slot with your thumb, working across. If it resists, tap it home with a rubber mallet or the side of your fist against a wood block. Do not use a metal hammer directly on the bulb.
Step 4: Install the Sides
Cut each side piece to your measurement. Most kits are meant to run from the top corner down to the threshold, with the bottom end touching the threshold or the corner pad. Start at the top, press the fin in every few inches first to hold it, then go back and seat the whole length.
For adhesive foam, peel back only 6 to 12 inches of backing at a time so the strip doesn't stick to itself. Press it to the center of the door stop so the door compresses it when closed. Adhesive products generally need temperatures above about 40 to 50°F to bond, so on a cold day warm the jamb with a hair dryer first, and check the label for the minimum.
Step 5: Fix the Bottom
The bottom of the door is where most of the cold air gets in. There are two parts to look at.
Corner pads. Small foam pads sit at the bottom corners of the jamb, where the side weatherstrip meets the threshold. They are easy to overlook and cost a few dollars. Replace them if they are missing or crushed.
Sweep or bottom insert. If your door has a slide-in U-shaped bottom seal, pull the old one out of the slots on the door bottom, cut the new one to the door width, and slide it in. For a surface-mount sweep, close the door, hold the sweep against the inside face so the fin just touches the threshold, mark the screw holes, and screw it on. The fin should brush the threshold lightly, not fold over so hard that the door is difficult to close.
Many thresholds also have adjustment screws under removable caps. Turning them counterclockwise raises the threshold a little to meet the sweep.
Step 6: Test Again
Close the door and repeat the dollar bill test around the whole perimeter. The door should latch with a firm push and not need a slam. If it now won't latch at all, the new seal may be thicker than the old one; the strike plate can often be moved out about 1/16 inch, or the adjustable tab inside the strike can be bent slightly.
Common Mistakes
- Buying the wrong profile. Kerf-in strips are not universal. Bring a sample.
- Sticking foam to a dirty or cold surface. It will peel within weeks.
- Overstuffing the gap. A seal so thick that the door won't latch will wear out the latch and the strip fast.
- Forgetting the corners. A perfect strip with missing corner pads still lets air through at the floor.
- Treating a sagging door with weatherstrip. If the gap is wide at the top of the latch side and tight at the bottom, tighten the hinge screws first, or replace one top-hinge screw with a 3-inch screw that reaches the framing.
Is It Worth It?
Air leaks around doors and windows are a meaningful part of heat loss in many homes, and a new set of seals costs less than a single month of most heating bills. You also get a quieter entry, less dust under the door and fewer bugs. Spend an hour on your front door this weekend, then do the back door and the door to the garage, which is often the leakiest of the three.
