Single-pane and older double-pane windows can account for 25% to 30% of residential heat loss, according to Department of Energy estimates. Learning how to winterize windows properly returns that money to your wallet within a single heating season, often for less than $50 per window. The methods below are ranked by impact and cost so you can do the highest-return jobs first. Most homeowners can finish a typical 1,800 sq ft house in one weekend.
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Inspect Before You Seal
Walk the perimeter of every window on a windy day with a lit incense stick or a thin strip of toilet paper. Anywhere the smoke or paper deflects, you have an air leak. Mark each leak with a small piece of blue tape so you do not miss it later.
Check the meeting rail of double-hung windows, the latch side of casements, the corners of the trim, and the gap where the sash meets the sill. Older homes often leak around the window frame itself rather than the sash, which means caulking the trim is more effective than sash repairs.
Caulking and Weatherstripping
Apply a 1/4-inch bead of paintable acrylic latex caulk (DAP Alex Plus or similar, $4 a tube) where window trim meets siding or drywall. For exterior gaps wider than 1/4 inch, use a polyurethane sealant like Sikaflex 1a, which flexes with temperature changes.
For sash leaks, replace worn weatherstripping. V-strip vinyl (Frost King, around $6 per roll) presses into the channel and seals when the sash closes. On wood double-hung windows, swap broken sash chains and add tubular silicone bulb gaskets to restore the seal between the upper and lower sash.
Window Insulation Film Kits
Heat-shrink film, sold by 3M Indoor Window Insulator Kits ($12 for 5 windows), is the highest-return weekend project in the entire winterization toolbox. Apply double-sided tape around the trim, stretch the film over the opening, then shrink it tight with a hair dryer. The trapped dead air space adds an R-value boost equivalent to going from single to double pane.
Film is nearly invisible after shrinking and removes cleanly in spring. Skip it on windows you open for ventilation through winter; use it on bedroom and basement windows that stay closed.
Storm Windows: Interior and Exterior
Interior storm windows like Indow Inserts ($25 to $40 per sq ft) press into the existing window frame with a silicone tube and remove without tools. They cut sound transmission and add R-2 to single-pane glazing. The Window Saver kit from Window Solutions sells DIY interior storms in kit form for $80 to $140 per window.
Exterior triple-track storm windows from Larson or Andersen run $250 to $450 installed and last 25 years. They are the most cost-effective alternative to full window replacement on historic homes where original sashes must be preserved.
Heavy Curtains and Cellular Shades
Insulated curtains and cellular (honeycomb) shades trap a layer of dead air against the glass. Hunter Douglas Duette double-cell shades carry an R-value up to 4.6, comparable to double-pane glass alone. Levolor cellular shades from Lowes run $80 to $200 depending on size.
For curtains, look for the thermal-lined options from Sun Zero or Eclipse ($25 to $60 per panel) and mount the rod 4 inches above and 6 inches outside the window trim so the curtain seals against the wall, not the trim.
Plastic Sheeting for Basement and Garage
Basement and garage windows usually need not look pretty. A 6-mil polyethylene sheet (under $20 for a 10×25 roll) stapled to the frame, with edges sealed using 3-inch poly tape, blocks 100% of air infiltration. This works especially well on hopper and awning windows that are frequently the leakiest in the house.
Glazing Putty for Old Wood Windows
If you can see daylight where the glass meets the wood sash, the glazing putty has failed. Scrape out the cracked putty with a stiff blade, prime the wood with linseed oil, then apply new glazing compound (DAP 33, $8 per pint) with a putty knife. Allow 7 to 14 days to skin over before painting.
This single fix, on a 100-year-old farmhouse with 12 sashes, can drop heating costs by 15% on its own. Plan a full afternoon per sash including paint.
What Not to Bother With
Window draft snakes (the long fabric tubes you lay across the sill) look cute but block at most 5% of air infiltration. Skip them in favor of weatherstripping the actual leak. Bubble wrap on windows works thermally but looks awful and traps moisture against the glass, leading to mold on wood frames within one season.
When to Replace Instead of Winterize
- Glass packs are foggy from a broken seal (single pane fix is replacement, not film)
- Frame is rotted to the touch with a screwdriver
- Sashes will not stay open or closed without props
- Combined cost of repairs exceeds 50% of replacement cost (typically $400 to $1,000 per window)
FAQ: Winterize Windows
How much can I save winterizing windows? Most homes save 10% to 25% on heating bills depending on baseline window quality and method used.
Is window film worth it? Yes, easily the best ROI item. A $12 kit covers 5 windows and pays back in one month of heating savings.
Can I winterize from outside? Yes, exterior caulking and storm windows work from outside; film and curtains work from inside.
Will weatherstripping damage my windows? Properly sized self-adhesive strips will not. Avoid foam tape on operable sash; it crushes and fails fast.
When should I winterize? Before the first hard freeze, ideally when daytime temperatures are above 50 degrees Fahrenheit so caulk and adhesive cure properly. In most northern states this means finishing the work by mid-October; in the Sun Belt you can stretch into November without losing much heating savings for the season.
