Drafty windows waste energy, make rooms uncomfortable, and increase heating and cooling bills. The gaps that let cold air in during winter also let conditioned air out during summer. Most window drafts can be eliminated with inexpensive weatherstripping, caulk, and simple repairs that take less than an hour per window.

How to Fix Drafty Windows

Finding the Drafts

On a cold or windy day, hold your hand near the window edges, paying attention to where the sash meets the frame, where the frame meets the wall, and along the bottom rail. You will feel cold air moving through gaps.

For more precision, hold a lit incense stick near the window edges. The smoke stream deflects visibly when it hits a draft. A laser thermometer aimed at the window area versus the surrounding wall also reveals temperature differences indicating air infiltration.

Seal the Gap Between Frame and Wall

If drafts come from where the window frame meets the wall (the exterior trim or interior casing), the caulk seal has failed.

Remove old, cracked caulk with a putty knife or oscillating tool
Clean the surfaces
Apply a bead of siliconized acrylic latex caulk along the joint
Tool the bead smooth with a wet finger
If gaps are wider than 1/4 inch, fill with foam backer rod first, then caulk over it

This addresses the most common source of window drafts and can reduce air infiltration significantly.

Weatherstrip the Sash

The sash (the moving part of the window) should seal against the frame when closed. Over time, existing weatherstripping compresses, cracks, or falls off.

Types of Weatherstripping

V-strip (tension seal): A self-adhesive plastic or metal strip folded into a V shape. It presses against the mating surface when the window closes. Durable, nearly invisible, and effective. Best for double-hung windows along the sides of the sash.

Foam tape: Self-adhesive closed-cell foam in various thicknesses. Easy to install, inexpensive, but compresses over time and needs replacement every 1 to 3 years. Good for casement windows and as a temporary fix.

Tubular rubber or silicone: A flexible tube attached to a mounting strip. Compresses and rebounds effectively. More durable than foam. Good for the bottom rail of double-hung windows.

Felt: Inexpensive and easy to install but wears out quickly. Adequate for low-traffic windows but not recommended as a long-term solution.

Installation

Clean the surface where the weatherstripping will be applied
Measure and cut the weatherstripping to length
For peel-and-stick types, remove the backing and press firmly into place
For V-strip, apply along the channel where the sash slides
Close the window and check that it seals firmly without excessive resistance

Fix the Window Lock

A window lock that does not pull the sash tight against the frame creates a gap. If the lock does not engage fully:

Check if the lock is loose — tighten the mounting screws
If the lock aligns but does not pull tight, add a shim behind the keeper plate (the part the lock latches into) to bring the sash tighter
Replace the lock if it is worn or broken — standard window locks cost $3 to $8 at any hardware store

Window Insulation Film

For older single-pane windows or windows you do not open during winter, shrink-fit window insulation film adds a layer of insulating air space.

Apply double-sided tape around the window frame
Press the film onto the tape
Shrink the film tight with a hair dryer

The result is nearly invisible and remarkably effective at reducing drafts and heat loss. Remove it in spring and reapply each fall.

Window Draft Stopper

A fabric tube filled with sand, rice, or foam placed along the bottom of the window sill blocks cold air from flowing in along the bottom rail. This is a simple stopgap measure for the worst windows while you plan a more permanent fix.

When to Replace Windows

Repair and weatherstrip when:

The frames are sound and the glass is not broken
Drafts are around the edges (seal-able)
The windows operate correctly

Replace when:

The frames are rotted or warped
Glass seals have failed (foggy between double-pane glass)
The windows do not open, close, or lock properly
Energy costs justify the investment in modern windows

Most window draft issues are maintenance problems, not replacement problems. A $20 investment in weatherstripping and caulk per window eliminates most drafts and pays for itself in energy savings within a single season.