On this page
Many Canadian homes that get replacement windows still have units from an earlier generation: aluminum sliders, single-glazed wood windows with storm sashes, or early vinyl windows whose seals and hardware have given out. The job can be an insert inside the existing frame or a full-frame replacement down to the rough opening, and that choice shapes the result as much as the window you pick.
This page helps you tell when replacement is really needed, compares replacing the thermos with replacing the whole window, weighs an insert against a full-frame installation, compares frame materials, and covers ENERGY STAR, incentive programs and the permit questions that come up with bedroom and basement windows.
Signs your windows need replacing
- Fog, streaks or droplets between the panes that won't wipe away, meaning the seal of the sealed unit has failed.
- Cold drafts at the sashes or around the frame that remain even after the weatherstripping has been renewed.
- Soft, dark or crumbling wood on the sill, the bottom rail of the sash or the frame, often hidden under peeling paint.
- Windows that are hard to open, won't stay open or won't lock, especially when replacement parts are no longer made.
- Thick frost or ice building up on the inside of the glass or frame through much of the winter.
- Single glazing, or aluminum frames without a thermal break that turn icy cold to the touch.
- Water marks on the sill or the wall below the window after rain, a sign the frame or its seal no longer sheds water.
Thermos replacement or a new window: when repair is enough
A fogged sealed unit doesn't automatically call for a new window. Natural Resources Canada's guide to upgrading windows notes that when the seal of a double-glazed unit fails, the problem is best corrected by replacing the glazing unit, and a glazier can usually order a new thermos to size and fit it in the existing sash. Worn cranks, hinges, balances and weatherstripping can also be replaced on many windows.
The same guide suggests it may be time to replace the whole window when the frame is in poor condition. Replacement also makes sense when problems pile up, such as failed seals on several units, rotten sills and hardware that can no longer be found, or when the old window is single-glazed and the goal is a real gain in comfort.
- Replace the thermos: the frame and sash are sound, the window works well and only the glass has fogged or cracked.
- Repair the hardware: the glass is clear, but the crank spins freely, the sash won't latch or a balance has broken.
- Replace the window: the frame or sill is rotten, the unit lets water in or several parts have failed at once.
- Replace the window: it is single-glazed, or so old that parts and suitable glass are no longer available.
Insert (retrofit) or full-frame window replacement: pros and cons
With an insert, sometimes called a retrofit, the old sash and hardware come out and a complete new window is set inside the existing frame. It barely disturbs the interior trim or the exterior siding, goes quickly and, according to Natural Resources Canada, can be a good option for heritage homes. It only works if the existing frame hasn't deteriorated, and because the new frame sits inside the old one, the glass area shrinks a little.
A full-frame replacement, or complete tear-out, removes everything down to the rough opening. It involves more labour and new trim, but it lets the installer inspect the framing, fix hidden rot and properly air-seal and insulate the gap between the window and the wall, a benefit NRCan points to for this approach. It is also the only route when you want to change the size or style of an opening.
- An insert suits sound, dry frames, homes where interior trim or exterior masonry should stay untouched, and heritage facades.
- A full-frame replacement suits rotten or out-of-square frames, visible leaks around the old window and walls whose openings were never air-sealed.
- Full-frame is also needed to change the size, shape or opening style of a window, or to add the sill flashing the old installation lacked.
- Either way, ask the contractor to show you the condition of the existing frame before the final choice, not only once the old window is out.
Replacement window frame materials: vinyl, fibreglass, wood and aluminum-clad wood
Frame material affects upkeep, looks and how the window copes with Canada's temperature swings. Natural Resources Canada notes that while aluminum conducts heat more than non-metals, a window's overall energy efficiency depends more on the design of the product, so compare certified ratings rather than assuming one material always wins.
- Vinyl (PVC): a very common replacement choice, low-maintenance and well insulated, with welded corners; dark colours and very large units need a reinforced frame to limit movement in the heat.
- Fibreglass: stiff and stable, it expands at roughly the same rate as glass, which is easier on the seals, and it can be painted; frames can be slimmer than vinyl for the same strength.
- Wood: warm and traditional, often the right choice for heritage facades, but it needs regular painting or staining outside to keep rot away.
- Aluminum-clad wood: a wood interior with an aluminum skin outside, combining the look of wood indoors with an exterior that needs little upkeep.
- Hybrid PVC and aluminum: common in Quebec, a vinyl window with aluminum cladding outside that adds rigidity and a wider choice of exterior colours.
ENERGY STAR replacement windows and energy-efficiency incentives
Replacement windows sold as ENERGY STAR certified in Canada meet Natural Resources Canada's national criteria, and NRCan also recognizes ENERGY STAR Most Efficient windows and sliding glass doors, the top performers among certified models. The label on each unit lists its ratings, so you can compare quotes on the same basis and check that the model on the invoice is the one you were quoted.
Incentive programs for windows come and go, and their conditions change often. Some are run by provinces, others by utilities or municipalities, and many ask for an energy evaluation before the work, certified products or a registered contractor. Natural Resources Canada keeps a directory of energy efficiency programs across the country; check what is open where you live and read the conditions before you sign or order, since removing the old windows too soon can make a project ineligible.
Permits and egress rules for replacing bedroom and basement windows
Building codes generally require bedrooms, including those in basements, to have a window or another way out that a person can use to escape a fire, with rules on the size of the opening and how it opens. A replacement can break that rule without anyone noticing: an insert makes the opening smaller, and a sliding window offers less clear space than a casement of the same size. Check with your municipality before choosing the style of a bedroom window, especially in a basement or an older house.
Beyond egress, a permit may be needed when the size or position of an opening changes or when the facade is in a heritage area. In a condominium, check the declaration first, since windows are often treated as common property and the board's approval may be required.
Window Replacement: frequently asked questions
Can I replace just the glass instead of the whole window?
Yes, if the frame and sash are in good shape. A glazier measures the sealed unit and orders a new thermos to size, which keeps the existing frame and trim. If the frame is rotten or the window no longer closes well, new glass won't solve the real problem.
Why is there fog between the panes of my window?
The seal around the edge of the sealed unit has failed, letting moist air in between the panes, and any insulating gas can escape the same way. The fog won't clear on its own; the fix is a new sealed unit or, if the frame is also worn, a new window.
Is it worth replacing windows that still work?
Not always. If the windows are double-glazed, operate well and show no rot or failed seals, maintenance and the odd thermos replacement may be the better choice. Replacement makes more sense for single-glazed, drafty or rotting units, or when you're already redoing the siding or interior finishes around them.
Vinyl or fibreglass: which is better for replacement windows?
Both can perform well. Vinyl is widespread and needs little upkeep; fibreglass is stiffer and more stable, which suits large units and dark colours. Compare the certified U-factor or ER, the frame profile and the warranty of the specific models you're quoted.
Do I need a permit to replace my windows?
It depends on your municipality. Same-size replacements are often simpler, but a change in the size of an opening, a heritage facade or a bedroom window that must remain an emergency exit can all call for approval. Ask the city before ordering.
Are there rebates for replacing windows?
Sometimes. Provinces, utilities and some municipalities run programs that change from year to year, and they usually have conditions to meet before the work starts. Check Natural Resources Canada's directory of energy efficiency programs and the program's own rules before you order.
Sources
- Keeping the Heat In, Section 8: Upgrading windows and exterior doors — Natural Resources Canada
- ENERGY STAR certified windows, doors and skylights — Natural Resources Canada
- 2025 labelling requirements for ENERGY STAR fenestration — Natural Resources Canada
- Directory of Energy Efficiency Programs in Canada — Natural Resources Canada
Written by the LokalMatch editorial team. Reviewed by Zubair Afzal on September 10, 2026. How we write and check our guides