How to Seal Drafty Windows and Doors, Caulk vs Weatherstripping

A cold draft near a window or under a door is one of the cheapest problems in a house to fix, as long as you pick the right material. The U.S. Department of Energy (DOE) splits the job into two tools with two different purposes, and most failed weekend sealing projects come from using one where the other belongs.

The one rule that decides which material you need

DOE's Energy Saver guidance draws the line by movement:

• Caulk seals cracks and gaps between parts of the house that do not move, such as the joint between a window frame and the wall.
• Weatherstripping seals the gaps around parts that do move, such as a door against its jamb or a window sash sliding in its track.

DOE also sets a size limit for caulk: it is meant for cracks, gaps, or joints less than a quarter inch wide. Bigger gaps call for a different product, such as low-expansion foam, rather than a thicker bead of caulk.

Why bother: insulation does not stop air

DOE's Consumer Guide to Air Sealing explains the difference with a clothing comparison. Insulation works like a sweater: it slows heat moving through a surface, but it does not stop wind. Air sealing is the windbreaker. Leaks make rooms feel drafty, force heating and cooling equipment to work harder, and can carry moisture into wood framing, where it can lead to warping and mold.

The same guide adds a safety note worth reading before any big sealing project. Sealing and ventilation go together, because homes with fuel-burning appliances (furnaces, water heaters, gas stoves, fireplaces) need enough air to vent combustion gases safely. DOE recommends a professional assessment for whole-house sealing for exactly this reason. Sealing a few obviously leaky windows and doors is a normal DIY job; tightening an entire house is a bigger decision.

Choosing a caulk

DOE's caulking table compares common compounds. A few of the practical differences:

Caulk type	Good for	Notes from DOE's table
Household silicone	Bath and kitchen fixtures, tile, metal joints	Little or no shrinkage; cured silicone stretches to about three times the joint width; paint will not stick to most cured silicone
Latex	Joints around tubs and showers, cracks in tile and plaster, nail holes	Water cleanup, shrinks 5 to 10 percent, can be painted, lasts 2 to 10 years, will not stick to metal
Butyl rubber	Dissimilar materials such as glass, metal, and concrete; flashing	Lasts 10 years or more, but shrinks 5 to 30 percent and may need two applications
Oil or resin-based	Exterior seams	Cheapest of the group, but lasts only 1 to 4 years

For the common job of sealing an interior window trim joint you plan to paint, latex fits. For a joint that flexes or stays wet, silicone holds up better, as long as you do not need to paint over it.

How much to buy

DOE gives two simple planning numbers:

• Caulk: about half a cartridge per window or door.
• Weatherstripping: add up the perimeters of every window and door you plan to seal, then add 5 to 10 percent for waste.

A worked example for two 36 by 60 inch windows and one 36 by 80 inch door:

1. Each window perimeter: 2 × (36 + 60) = 192 inches.
2. Door perimeter: 2 × (36 + 80) = 232 inches.
3. Total: 192 + 192 + 232 = 616 inches, or about 51.3 feet.
4. Plus 10 percent for waste: about 56.5 feet, so plan on roughly 57 feet of weatherstripping.

For caulk, three openings at half a cartridge each is 1.5 cartridges, so buy 2.

Applying caulk the DOE way

DOE's tips are short and specific:

1. Clean first. Remove old caulk and paint with a putty knife, a large screwdriver, or a stiff brush, and make sure the surface is dry so you do not seal moisture in.
2. Hold the gun at about 45 degrees. You know the angle is right when caulk is pushed into the crack as it leaves the tube.
3. Use one continuous bead where you can, and make sure it sticks to both sides of the gap.
4. Release the trigger before pulling away to avoid excess.
5. Reapply if it shrinks. A bead that pulls back leaves the gap open.

Timing matters too. DOE says the best time to caulk is during dry weather above 45°F, since low humidity and warm temperatures help caulk set and adhere. In much of the country, that makes early fall a better caulking window than late fall.

Applying weatherstripping

Weatherstripping is more forgiving on temperature: DOE says it should go on clean, dry surfaces above 20°F. The rest of the guidance is about fit:

• Measure twice before cutting.
• The strip should compress when the door or window is closed, but not make it hard to shut.
• On doors, run one continuous strip along each side, make the corners meet tightly, and choose a matching door sweep or threshold for the bottom.

DOE's weatherization job aid for exterior doors adds an often-skipped step: fix the door first. Visible daylight or a loose fit around a door can come from loose hinges, knobs, or strike plates, and tightening those before you install new stripping gives the seal something square to press against. The job aid also notches the side pieces where they meet the top piece and checks that the door still opens and closes smoothly at the end.

Key takeaways

• Caulk is for gaps under a quarter inch between parts that do not move; weatherstripping is for parts that do move.
• Plan on half a cartridge of caulk per window or door, and add 5 to 10 percent to the total perimeter when buying weatherstripping.
• Caulk in dry weather above 45°F at a 45-degree gun angle; weatherstripping can go on above 20°F.
• Fix loose hinges and strike plates before weatherstripping a door, and check that it still closes easily afterward.
• Sealing a few windows and doors is a weekend job, but whole-house air sealing in a home with fuel-burning appliances deserves a professional assessment of ventilation first.