Interactive Window Technology Demo: How Modern Windows Work

U-factor measures how much heat passes through a window, in W/m²·K. Lower is better. Single-pane sits around 5.0, while modern double-pane with Low-E and argon is 1.4–1.6. Aim for 1.40 or lower for Energy Star qualification and rebate eligibility.

Solar Heat Gain Coefficient measures how much solar heat passes through the glass, from 0 to 1. The best value depends on orientation: south-facing windows benefit from 0.30–0.40 and west-facing from 0.20–0.25. A balanced 0.22–0.35 works for most BC homes.

Low-E 270 is a passive coating with an SHGC of about 0.34, suited to north and east windows. Low-E 366 is a solar control coating with an SHGC of about 0.22, better for south and west exposures. Many homes use both.

Triple-pane raises glass costs 30–50% but delivers a U-factor of 0.8–1.0 versus 1.4–1.6 for double-pane. It is most valuable for large north-facing windows, bedrooms and noise-sensitive rooms. For most BC homes, double-pane with Low-E and argon is the better value.

Argon is an inert gas that conducts less heat than air. Sealed between the panes, it reduces convection and conduction and improves insulation by roughly 30% over air-filled units. It is colourless, odourless and non-toxic.

Check four numbers: U-factor (lower is better), SHGC (depends on orientation), visible transmittance (typically 0.40–0.70 for natural light) and Energy Rating (higher is better, 25+ for Energy Star). ER is unique to Canada and balances heat loss against solar gain.

The frame contributes about 20% of a window’s total U-factor. Multi-chambered vinyl frames trap still air, which slows heat transfer without the upkeep of wood.

Aluminum spacers create a thermal bridge at the glass edge and cause condensation. Warm-edge spacers can cut edge heat loss by up to 65%, keeping the edges warmer.