How to Insulate Windows for Winter on the Cheap

The Short Answer

Windows are one of the weakest parts of a house in winter. South Carolina’s state energy office puts it at 25–30 percent of residential heating and cooling energy use. You don’t need new windows to cut that: the cheap fixes below stop drafts and add an insulating layer, and all of them come off in spring.

Two kinds of loss matter. Drafts (air leaking around the sash and frame) are fixed by sealing. Cold glass (heat conducting through the pane) is reduced by adding a layer: film, a curtain or a shade. Most drafty windows need both.

1. Rope Caulk for the Gaps

Rope caulk is a soft, putty-like cord you press into gaps around the sash and frame. Avista, a utility, describes it as a lot like modeling clay and notes it is easy to remove in the spring. That makes it ideal for rentals and for sashes you will want to open again.

Find the gaps first: on a windy day, move a lit incense stick around the frame and watch the smoke. For sashes that need to keep opening year-round, weatherstrip instead; the Department of Energy’s Building America guide covers which type goes where.

2. Shrink Film (Interior Window Kits)

A window film kit stretches a clear plastic sheet across the inside of the frame, creating a still air layer. ENERGY STAR says these covers are inexpensive, reduce drafts, help the house feel warmer during winter months. You apply double-sided tape to the frame, press the film on and use the hair dryer to tighten the film.

Use it on windows you won’t open until spring. Take it off slowly so the tape doesn’t lift paint. Which kit to buy: see our window insulation kits compared (3M, Duck and Frost King, by cost per window).

3. Draft Stoppers

A weighted fabric tube along the sill or the bottom of a door blocks the air that slides in underneath. Virginia’s state energy program calls them a simple, portable form of weatherstripping. They are only as good as their contact with the sill, so press them firmly into place. For the gap under a door, a stick-on strip or a screw-on sweep seals better; our picks are in the best door draft stoppers.

4. Curtains: Close at Night, Open by Day

Use your curtains as a switch. Minnesota’s Commerce Department advises you to open curtains on south-facing windows during the day to let the sun in and close them at night to reduce the chill from cold windows.

Set expectations, though: Cornell Cooperative Extension says conventionally hung draperies will reduce window heat loss no more than 10 percent. Heavy, lined curtains that touch the sill and wall, with a closed top, do better than loose ones.

5. Cellular Shades for the Coldest Rooms

Cellular (honeycomb) shades trap air in their cells and fit inside the frame. In a Department of Energy study, cellular shades saved up to 20% on heating energy. They cost more than film or curtains but last for years and work in summer too.

Which Fix to Use First

For a longer-term fix that still keeps your windows, the Department of Energy says low-e storm windows can save you 10%–30% on heating and cooling costs. See our windows guide before paying for replacements.

Cheap Fixes We’d Buy

We may earn a commission if you buy through these links, at no extra cost to you. Products are chosen on published specifications; we do not test them in-house (how we choose).

Frost King B2 Mortite Caulking Cord

Rope caulk for gaps around frames and sashes. Presses in by hand and peels out in spring.

Check price on Amazon

3M Indoor Window Insulator Kit

Shrink film for the windows you won’t open until spring.

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Holikme Under-Door Draft Stopper

A weighted stopper for a drafty sill or the bottom of a door.

Check price on Amazon

NICETOWN Thermal Blackout Curtains (grey)

Lined curtains for the coldest room. Close them at night.

Check price on Amazon

Frequently Asked Questions

What is the cheapest way to insulate windows for winter?

Rope caulk for gaps around the frame and an interior shrink-film kit for the glass. Both are inexpensive and come off in spring.

Does window insulation film really work?

ENERGY STAR says film covers are inexpensive, reduce drafts and help the house feel warmer in winter. There is no reliable figure for the exact energy saved.

Do thermal curtains keep heat in?

Somewhat. Cornell Cooperative Extension says conventionally hung draperies reduce window heat loss by no more than 10 percent. Close them at night and open south-facing ones by day.

How much heat is lost through windows?

South Carolina's state energy office says windows are responsible for 25 to 30 percent of residential heating and cooling energy use.

Are cellular shades worth it?

In a Department of Energy study, cellular shades saved up to 20% on heating energy. They cost more than film but last for years.

Related Guides

• Do new windows lower energy bills? — storm windows vs replacement
• Window treatments and energy savings — shades and curtains compared
• Drafty rooms checklist — the rest of the room
• Door weatherstripping — the other big draft
• Best window insulation kits and door draft stoppers — the products, compared
• Best thermal curtains for winter — which to buy and how to hang them
• Electric blanket vs space heater — the cheaper way to stay warm at night

Sources

• South Carolina Energy Office: Windows
• Cornell Cooperative Extension: Energy-saving window treatments
• Avista: Rope caulk
• ENERGY STAR: Plastic over windows
• Minnesota Commerce: Winter energy tips (PDF)
• U.S. Department of Energy: Cellular shades fact sheet (PDF)
• Virginia Energy Sense: Draft stoppers
• U.S. Department of Energy: Storm windows
• Building America Solution Center: Add weatherstrip