Energy-Efficient Window Coverings and Window Film: What Works in Ontario

Energy-efficient window coverings, such as cellular shades, insulated curtains and window film, can reduce heat loss through windows in an Ontario winter and keep out solar heat in summer, at a fraction of the cost of new windows. They work best when they fit tightly, are used every day, and are matched to the season: closed at night in winter, open on sunny winter days and closed against afternoon sun in summer.

They are also one of the few upgrades renters can do. This guide compares the main options, gives realistic savings ranges and explains when coverings are not enough.

How much heat do windows lose?

Even good windows insulate far less than walls. A typical double-glazed window in an older Ontario home is roughly R-2 to R-3, while a single-pane window is about R-1. A modern triple-glazed window might reach R-5 to R-8. By comparison, an insulated 2x6 wall is around R-20 or more.

Windows also leak air around sashes and frames, and in summer they let in solar heat. That is why coverings can make a noticeable difference in comfort, even if the effect on the whole-house bill is moderate.

What are the options for energy-efficient window coverings?

Option	Winter benefit	Summer benefit	Rough cost per window (estimate)	Notes
Cellular (honeycomb) shades	Good; better with side tracks	Moderate	$80 to $300+	Double-cell types insulate more
Insulated or lined curtains	Moderate to good if sealed at top and sides	Moderate	$50 to $200	Use a cornice or wall-mounted rod to reduce air circulation
Plastic shrink film (interior)	Good on single-pane or drafty windows	None	$5 to $15	Seasonal; blocks opening
Low-e retrofit film	Moderate	Good	$8 to $20 per ft² installed	Check glass type and warranty
Solar control film	Little or negative	Good	$6 to $15 per ft² installed	Can block useful winter sun
Exterior awnings or shutters	Little	Very good	$300 to $1,500+	Best summer option for south and west windows
Interior blinds (venetian)	Little	Low to moderate	$30 to $150	Light control more than insulation

The savings depend on window size, orientation, your heating fuel, and above all how consistently you use them.

Winter: keeping heat in

Cellular shades

The honeycomb pockets trap air, much like a thin layer of insulation. Fit matters: a shade mounted inside the frame with small side gaps works noticeably better than one with large gaps. Shades with side tracks or a closed-top design are the most effective.

As a rough estimate, a well-fitted cellular shade can reduce heat loss through the window by about a third or more when closed. Leave them open on sunny days, especially on south-facing windows, to collect free solar heat.

Curtains

Heavy, lined curtains help most when they reach the floor or sill, overlap the window on each side and are closed at the top with a valance or cornice. Without that, warm room air circulates behind the curtain, cools against the glass and falls out the bottom, which can make a room feel draftier.

Caution: Do not block baseboard heaters, radiators or floor registers with long curtains. Leave space for warm air to circulate and keep fabrics clear of electric heaters for fire safety.

Plastic shrink film

Window insulation kits use double-sided tape and a clear film tightened with a hair dryer. They add a still-air layer and stop drafts. For single-pane windows, old wood sashes and basement windows, this is the best value per dollar of any option. The downside is appearance and the window cannot be opened until spring.

Low-e retrofit film

Low-emissivity film is applied to the inside surface of the glass and reflects heat back into the room. It can lower heat loss modestly and also reduces summer heat gain.

Before installing it:

• Check the window warranty. Many manufacturers void the glass warranty if film is applied.
• Ask about thermal stress. Dark or highly absorbing films can cause cracking on some double-glazed or large windows. A reputable installer will check the glass type.
• Consider the view. Some films slightly tint the glass.

Summer: keeping heat out

In Ontario summers, west-facing and south-facing windows can drive much of a home's cooling load in the late afternoon.

1. Shade the outside first. Exterior awnings, shutters, pergolas and deciduous trees stop sunlight before it reaches the glass. Interior blinds stop light after it has already turned to heat inside the room.
2. Close coverings on sunny sides during the hottest hours.
3. Use light-coloured or reflective backings on shades facing the sun.
4. Consider solar control film on west windows that cannot be shaded outside, but avoid it on south windows that help heat the home in winter.

Our guide to summer cooling savings covers air conditioner and ventilation tips that go with shading.

What savings can you expect?

Here is an illustrative estimate for a gas-heated Toronto-area home with 12 older double-glazed windows totalling about 15 m² (160 ft²), with cellular shades closed every night through the heating season.

Item	Estimate
Heat loss through these windows	Roughly 8 to 12% of total heating
Reduction averaged over the day, with shades closed overnight only	15 to 25% of window heat loss
Annual gas saved	About 30 to 60 m³
Value at 45¢/m³	About $15 to $30 per year

With gas heat, savings alone will not pay for premium shades quickly. The picture is better with electric baseboard heat, where the same reduction could be worth several times as much, and the comfort benefit near cold windows is noticeable in any home. Use our insulation savings calculator for a rough comparison with other upgrades.

When coverings are not enough

Coverings cannot fix rotten frames, failed seals (fogging between panes), or large air leaks around the frame. If windows are near the end of their life, replacement may be the better long-term choice, and window and door upgrades can qualify for $100 per rough opening through the assessment stream of the Home Renovation Savings Program. Confirm details on saveonenergy.ca (opens in a new tab). Our windows and doors upgrade guide explains when replacement is worth it.

Before buying coverings, seal drafts around frames and trim with caulk and weatherstripping. Our air sealing guide shows where to start.

Frequently asked questions

Do thermal curtains really work?

They help if they are sealed at the top and sides and closed at night. Loose curtains hung on a rod well above the window do much less.

Will window film damage my double-pane windows?

Some films can cause thermal stress cracks on certain glass types, and many window warranties exclude film. Ask the installer to confirm the film is compatible with your glass.

Can renters use these options?

Yes. Tension-mounted or removable shades, curtains and shrink film kits are generally renter-friendly. Check your lease before installing anything that requires drilling. See our guide to energy savings for renters and condo owners.

Should I keep blinds closed all winter?

No. Open them on sunny days, especially on south-facing windows, and close them at night. Free solar heat on a clear winter day can be significant.