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How to Buy Windows for a New House in Ontario: The Four Numbers, Frame Materials, Glass, and Where to Spend
Finishes and upgrades Windows From a builder
How to Buy Windows for a New House in Ontario: The Four Numbers, Frame Materials, Glass, and Where to Spend
Windows are holes in the wall with glass in them, and in an R-22 wall a double-pane window is an R-3 hole. People choose them by the look. If you could see heat loss the way you see colour, the energy numbers would be the first thing on the list, so here they are first.
Short version: Read four numbers on the label: U-value (heat loss, lower is better; 1.4 W/m2K is Code territory, 1.0 or under is triple-pane), solar heat gain coefficient (0.4 or higher on south glass to collect winter sun, lower on west glass), air leakage (0.3 cfm per square foot or less, casements and awnings seal best), and the ENERGY STAR energy rating. Low-e coatings and argon fill are standard; warm-edge spacers stop the condensation at the edges. Frames: vinyl is the value, fibreglass is the premium that moves with the glass and takes dark colours, wood is beautiful and needs upkeep, aluminum belongs in warm climates. In 2026 budget $900 to $2,000 per window installed for good double-pane and 15 to 30 percent more for triple; put the triples on the north and the lake side first, and order them before framing because the lead time is 8 to 14 weeks.
The four numbers
| Number | What it measures | What to look for in Ontario |
|---|---|---|
| U-value (W/m2K) | Heat loss through the whole unit, glass and frame; lower is better | SB-12 packages top out around 1.4 to 1.6; good double-pane low-e argon is 1.2 to 1.4; triple-pane 0.8 to 1.1 |
| Solar heat gain coefficient (SHGC) | How much of the sun’s heat comes through | 0.4 or higher on south windows to collect free winter heat; 0.25 to 0.35 on west glass that overheats in summer |
| Air leakage | Air through the closed unit, cfm per sq ft | 0.3 or less; casements and awnings clamp tight, sliders and hung windows leak more |
| Energy Rating (ER) | A Canadian combined score of U, SHGC and leakage | ENERGY STAR for the zone; higher ER is better for a heating climate |
Ask for whole-unit values, not centre-of-glass; a manufacturer boasting “R-8 glass” is quoting the middle of the pane, and the frame and edge pull the real number down by a third. The best windows for an Ontario climate ranks the products; this page is how to read them.
Glass
- Low-e coatings: metallic oxide layers that reflect long-wave heat back into the room in winter and out in summer, while passing visible light. Standard now; the question is which coating. A high-gain low-e on the south, a low-gain one on the west.
- Gas fill: argon between the panes slows conduction; krypton is better and dearer and used in thin triples. Expect a few percent loss over 20 years; it barely moves the U-value.
- Double versus triple: a third pane and a second low-e coating cut the U-value by about a third and lift the inside glass temperature enough that condensation at minus 20 mostly stops. Triples are 15 to 30 percent more, heavier, and the right choice on the north wall, the wind side, big view glass and any bedroom you want quiet.
- Warm-edge spacers: the strip holding the panes apart; aluminum conducts and sweats, stainless, foam or composite spacers do not. Insist on them.
- Visible transmittance: how clear the glass looks; above 60 percent reads bright, below 50 reads tinted. Judge a sample outdoors.
- UV: most low-e glass blocks 75 percent or more of the UV that fades floors and fabric; ask for the number on a south wall of hardwood.
Frames
| Frame | Pros | Cons | 2026 installed, typical window |
|---|---|---|---|
| Vinyl | Inexpensive, rot-proof, no painting, good insulating value | Expands and contracts a lot, dark colours can distort, cannot be repainted; choose light colours and welded corners | $700 to $1,400 |
| Fibreglass | Strong, moves with the glass, takes dark colours, paintable, long life | More expensive | $1,000 to $2,000 |
| Wood, clad outside | The look, warm, repairable | Needs finishing inside, costs the most | $1,200 to $2,800 |
| Aluminum | Slim, durable | Conducts heat badly; a thermally broken frame is the minimum and still trails the others | $900 to $1,800 |
| Composite / hybrid | Vinyl or fibreglass outside, wood inside | Price | $1,100 to $2,400 |
Add 15 to 30 percent for triple-pane glass in any frame; large fixed view units and custom shapes are priced by the square foot and go up fast.
Operation
Casements and awnings crank open and clamp against the weatherstrip when closed; they are the tightest and the easiest to open from a chair. Sliders and single or double hung windows seal less well and are cheaper. Fixed glass is cheapest and tightest of all, and a wall of fixed glass with a few operable units for cross-ventilation is both the best-performing and the best-looking arrangement. Egress windows in bedrooms have minimum opening sizes under the Code; egress window requirements has them, and the basement is where people get caught.
Where to spend, where to save
- North and the wind side (the lake side on Georgian Bay): triple-pane, best U-value, casements.
- South: high solar gain glass, double or triple, with the overhang sized to shade it in July.
- West: low solar gain glass or exterior shading; this is the wall that overheats in August.
- Bedrooms: triples for quiet as much as for heat.
- Garage, mechanical room, the small bathroom window: standard double-pane is fine.
- Fewer, larger, better windows beat many small ones; every unit is a frame and a perimeter to seal. Choosing house plans is where the window count gets decided.
Ordering and installing
- Lead times run 8 to 14 weeks; the order goes in when the framing starts, not when the openings are cut.
- Rough openings and bucks (especially in ICF) are sized to the units, so the order has to be final before the pour or the framing.
- Installation decides half the performance: sill pan, flashing in shingle order, foam at the perimeter, interior air seal. Siding and the drainage plane and the before-drywall checklist cover the parts you can still see.
- Keep the labels on until the inspector and the energy evaluator have seen them.
Related guides on this site
Sources and further reading
Questions people ask
What window rating matters most in Ontario?
The whole-unit U-value (lower is better; 1.4 W/m2K is Code territory, 1.0 or under is triple-pane), then solar heat gain by orientation, then air leakage. Ask for whole-unit numbers, not centre-of-glass.
Are triple-pane windows worth it in Ontario?
On the north wall, the wind side, big view glass and bedrooms, yes: about a third less heat loss, far less condensation at minus 20, and quieter, for 15 to 30 percent more. Standard double-pane low-e is fine on small, sheltered openings.
Vinyl, fibreglass or wood windows?
Vinyl is the value choice in light colours with welded corners; fibreglass is the premium that stays stable, takes dark colours and lasts longest; wood is for the look and needs upkeep. Aluminum frames belong in warm climates.
When do windows have to be ordered on a new build?
When framing starts, because lead times run 8 to 14 weeks and the rough openings (or the ICF bucks) are built to the units. Changing a window after the openings exist costs money.
Building in Simcoe County or on Georgian Bay?
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Reviewed and updated October 2026. Costs are Ontario ranges, not quotes; code references are to the Ontario Building Code in force at that date.
It’s fascinating how adding a pane of glass improves the insulating value of a window about as much as low-E coatings do. Because glass windows are such lovely items, I wish to purchase some for my room. I appreciate the window buying advice, and I’m hoping to find a suitable window for my room soon.