How to Seal Drafty Windows (Cheap Fixes That Actually Work)

Frequently Asked Questions

How can I tell if my windows are drafty?

Hold a lit candle or incense stick near the window edges on a windy day. If the smoke wavers, you have a draft. You can also feel along the frame with your hand — cold spots indicate air leaks. A thermal leak detector ($25-40) pinpoints leaks precisely.

What is the cheapest way to seal drafty windows?

Rope caulk (also called mortite or Duck brand weatherstrip) is the cheapest and most effective. At $5-8 per window, it fills gaps around sashes and comes out cleanly in spring. No tools needed — just press it into the gap.

Does window insulation film really work?

Yes. Window insulation film creates a dead air pocket between the film and glass, similar to a second pane. It reduces heat loss by 40-55 percent and pays for itself in one heating season. The film is nearly invisible once shrunk with a hair dryer.

Should I replace drafty windows or just seal them?

Seal them first. Replacement windows cost $300-700 each with a 10-20 year payback period. Sealing reduces 60-80 percent of drafts for under $30 per window. Only replace if frames are rotting, glass seals have failed (foggy between panes), or windows won't open or close.

How long does weatherstripping last?

Foam weatherstripping lasts 1-2 years. V-strip or tension seal lasts 5-10 years. Silicone weatherstripping lasts 10+ years. Rope caulk is removable each spring, reapplied in fall.

Drafty windows are the second biggest source of heat loss in most homes, right after the attic. A single drafty window loses as much heat as leaving a small hole in your wall. Multiply that by every window in an older house and you’re looking at hundreds of dollars per winter in wasted heating costs.

The good news: you don’t need to replace your windows. Most drafts can be sealed for under $30 per window with products you can install in minutes. Replacement is a last resort — it costs 20-50x more and the energy savings rarely justify the expense.

Step 1: Find the Drafts

Before you start sealing, identify exactly where air is leaking.

The candle test: On a windy day, light a candle or stick of incense and slowly move it around the window frame. Where the flame wavers or smoke bends sideways, you have a draft. Common leak points:

• Top and bottom of the sash where it meets the frame
• Where two sashes meet in the middle (double-hung windows)
• Corners of the frame
• Along the sill
• Where the frame meets the wall

The hand test: Run your hand slowly along the window edges. Cold spots indicate air infiltration.

The thermal leak detector: For precise diagnosis, use a thermal leak detector ($25-40). Point it at the window and it shows temperature differences as colors — cold spots are leaks.

Infrared camera app: If you have an iPhone Pro or a FLIR attachment, thermal imaging shows leaks visually.

Step 2: Choose Your Sealing Strategy

Different leaks need different solutions. Here’s what works where:

Leak Location	Best Fix	Cost per Window
Gap around movable sashes	Rope caulk or V-strip weatherstripping	$5-15
Top/bottom of sash meeting frame	Foam weatherstripping	$3-8
Between two sashes (meeting rail)	V-strip weatherstripping	$5-10
Gap between frame and wall	Silicone caulk	$5 (covers multiple windows)
All glass surface (entire pane)	Window insulation film	$5-8
Interior (finished look)	Cellular shades or heavy curtains	$30-200

Fix 1: Rope Caulk (Best First Line of Defense)

Rope caulk is a putty-like strip you press into gaps. It’s cheap, effective, tool-free, and removable in spring.

How to apply:

1. Clean the window frame with soap and water. Dry thoroughly.
2. Peel off a length of rope caulk.
3. Press it into the gap along the sash where it meets the frame.
4. Smooth with your finger.
5. To remove in spring, pull it off with your fingers.

Best brands: Mortite, Duck Max Strength, Frost King. Cost: $5-8 per window. Time: 5 minutes per window. Effectiveness: Reduces drafts 40-60%.

Fix 2: Weatherstripping

For gaps that need a more permanent seal, use adhesive weatherstripping.

Foam Tape (Cheapest)

• Best for: Small gaps under 1/4 inch
• Lifespan: 1-2 years
• Cost: $3-8 per roll (covers 10-17 feet)
• Application: Peel adhesive backing, press onto clean surface

V-Strip (Best Balance)

• Best for: The gap between two window sashes, or any gap 1/4-1/2 inch
• Lifespan: 5-10 years
• Cost: $8-15 per roll
• Application: Peel backing or nail in place

Silicone Weatherstripping (Longest Lasting)

• Best for: High-use windows, permanent installation
• Lifespan: 10+ years
• Cost: $12-20 per window
• Application: Fits in a groove cut into the frame (more complex install)

For most homeowners: V-strip weatherstripping ($10-15 per window) is the sweet spot between cost, durability, and effectiveness.

Fix 3: Window Insulation Film (Winter Powerhouse)

This is the single highest-impact fix for drafty windows — and it looks nearly invisible once installed.

How it works: Clear plastic film attaches to the window frame with double-sided tape. Shrinking the film with a hair dryer creates a tight, clear barrier. The dead air space between the film and glass acts as insulation, similar to adding a second pane of glass.

Installation:

1. Clean the window frame.
2. Apply the double-sided tape around the perimeter of the frame.
3. Cut the film 2 inches larger than the window on all sides.
4. Press the film onto the tape, starting at the top.
5. Trim excess with a utility knife.
6. Use a hair dryer on high heat to shrink the film until it’s tight and clear.

Effectiveness: Reduces heat loss through glass by 40-55%. Cost: $5-8 per window for a quality kit. Time: 15-20 minutes per window. Catch: It’s seasonal — apply in fall, remove in spring.

Fix 4: Caulk Around the Frame

The gap between the window frame and the wall is often hidden behind trim, but cold air still leaks through.

How to seal:

1. Inspect trim around windows from inside and outside.
2. Look for gaps, cracks in caulk, or missing caulk.
3. Apply fresh exterior silicone caulk outside, and paintable latex caulk inside.
4. Smooth with a wet finger.

Cost: $5-8 per tube (covers 3-6 windows). Effectiveness: Seals a leak source that weatherstripping can’t reach.

Fix 5: Thermal Curtains or Cellular Shades

Heavy window treatments add another layer of insulation and dramatically cut drafts.

Cellular (honeycomb) shades: The pleated cells trap air, creating insulation. Top-performing cellular shades reduce heat loss by 40-60%.

• Cost: $30-200 per window depending on size and quality
• Installation: Inside-mount brackets, 30 minutes DIY

Thermal curtains: Heavy lined curtains that go from ceiling to floor and wall to wall. Look for ones with a thermal or blackout lining.

• Cost: $20-60 per panel
• Installation: Extend curtain rods 3-6 inches beyond window on each side
• Close at night in winter for maximum benefit

Combo approach: Cellular shades during the day, thermal curtains at night. Maximum insulation with minimum aesthetic compromise.

What NOT to Do

Don’t use duct tape or masking tape on sashes. The adhesive damages paint and wood when removed.

Don’t fully caulk a window shut. You need the window to open for emergencies, ventilation, and cleaning. Use removable rope caulk for the movable parts.

Don’t spray foam into the frame-to-wall gap. Expanding foam can warp the window frame and prevent the window from opening. If there’s a large gap, use backer rod first, then caulk.

Don’t replace the window before sealing. Replacement windows cost $300-700 each and take 10-20 years to pay back. Seal first, see how much it helps, then decide if replacement is needed.

When to Replace Instead of Seal

Some windows can’t be saved. Replace when:

• The frame is rotting. Soft or crumbling wood around the frame means water damage has compromised the structure.
• The glass seal has failed. If you see fog, moisture, or haze between the two panes of a double-pane window, the argon gas has leaked out. Sealing won’t help — the insulation value is already gone.
• The window won’t open or close. A warped frame or broken balance means the window is at end of life.
• Heavy single-pane windows in cold climates. If you have original single-pane windows in zones 5-7 (most of the northern US), upgrading to ENERGY STAR windows can reduce heating costs by 25-30%.

Replacement cost: $300-700 per window installed. See our energy-efficient window guide for more details on when replacement makes financial sense.

Cost/Benefit Summary

For a 15-window home, here’s what each approach costs and saves annually:

Approach	Total Cost	Annual Savings	Payback
Rope caulk + weatherstripping	$75-150	$80-150	1 year
Add insulation film	+$75-120	+$100-200	1 year
Add thermal curtains	+$300-600	+$50-100	6 years
Full window replacement	$4,500-10,500	$125-340	15-20 years

Best strategy for most homeowners: Combine rope caulk, weatherstripping, and insulation film ($150-270 total) for 60-80% of the benefit of replacement at 3-5% of the cost. Save window replacement for when windows fail structurally.

For complete seasonal prep, combine window sealing with our winterize your home checklist and annual home maintenance schedule.

Related Reading

• Eco-Friendly Home Improvements — energy efficiency upgrades that pair with sealing
• Best Smart Thermostats — cut heating costs further
• Attic Insulation Cost Guide — the #1 heat-loss source (windows are #2)
• Cost to Replace Front Door — the other major air-leak point