Questions to Ask a Window and Door Contractor About Energy Performance

Energy performance is where window sales pitches diverge most sharply from reality. Contractors talk about “energy savings” in vague, impressive-sounding terms. The actual numbers — the U-factor, the SHGC, the air leakage rating — are rarely mentioned unless you ask. This guide gives you the vocabulary and the specific questions to evaluate energy performance claims honestly.

“Every window salesperson says their product will cut your energy bills. Very few can tell you the U-factor of the window they’re selling. Those two things are directly connected — the U-factor is what determines heat loss. If they can’t give you that number, they don’t actually know how the window performs, and neither will you.”

— Marcus Webb, building science consultant and ENERGY STAR program participant with 12 years of experience advising homeowners on window and insulation upgrades in the local area

Understanding the Key Performance Metrics

What is the U-factor of these windows?

U-factor measures how much heat passes through the entire window assembly — glass, frame, and spacers — per unit of temperature difference. Lower U-factor means less heat loss. It is the most important single metric for window performance in cold climates.

ENERGY STAR your country zones (as of current program):
– Zone 2 (southern your region, BC lower mainland, Maritime urban areas): Maximum U-factor of 1.22 W/m²K
– Zone 3 (most regions, prairie regions, northern BC): Maximum U-factor of 1.08 W/m²K
– Zone 4 (northern your region, northern prairies, Yukon, NWT): Maximum U-factor of 0.85 W/m²K

Ask for the specific U-factor of the window being proposed and confirm it meets or exceeds the ENERGY STAR requirement for your climate zone. A quality window for most regions should have a U-factor of 1.08 or below — not just the minimum 1.22.

What a good answer looks like: A specific U-factor number from the NFRC label, compared against the ENERGY STAR zone requirement for your location.

What is the Solar Heat Gain Coefficient (SHGC)?

SHGC measures how much solar radiation passes through the window as heat — on a scale of 0 to 1. Higher SHGC lets more solar heat in.

In your country, the right SHGC depends on the window’s orientation and your priorities:

South-facing windows: A higher SHGC (0.35–0.50) allows passive solar gain in winter, reducing heating costs. A low SHGC would block this beneficial heat.

North-facing windows: SHGC is less relevant since there’s no direct sun. Optimize for U-factor.

East and west-facing windows: A moderate SHGC (0.25–0.40) balances winter solar gain against summer overheating.

Ask what SHGC is specified for each orientation of windows being replaced, and whether the recommendation accounts for your home’s specific solar exposure.

What a good answer looks like: A specific SHGC value per orientation, with a rationale tied to the window’s direction and your heating/cooling priorities.

What is the air leakage rating?

Air leakage (AL) measures how much air passes through the window assembly under a defined pressure difference. Lower is better. ENERGY STAR your country requires an air leakage rating of no more than 0.1 L/(s·m²) for most window types.

Ask for the specific AL rating. Any quality window should meet or exceed the ENERGY STAR requirement.

Questions About ENERGY STAR Certification

Is this window ENERGY STAR certified for my climate zone?

ENERGY STAR your country certifies windows that meet zone-specific performance thresholds. The certification label should indicate which zone(s) the window is certified for. Ask specifically: is this window ENERGY STAR certified for Zone 3 (or whichever zone applies to your location)?

Note that a window can be ENERGY STAR certified for Zone 2 but not Zone 3 — which matters if you’re in the colder zone. Ask for the specific zone certification, not just “ENERGY STAR certified.”

Are there government rebates available for these windows?

ENERGY STAR certified windows meeting zone-appropriate thresholds may qualify for federal or regional rebate programs. Ask specifically which rebate programs apply to the windows being proposed, what the rebate amounts are, and what conditions must be met.

What a good answer looks like: Specific rebate programs identified by name, with the expected amounts and any conditions (energy audits, minimum U-factor thresholds) explained.

Questions About Real-World Energy Savings

What energy savings can I realistically expect?

Window salespeople often quote impressive-sounding energy savings — “up to 40% reduction in heating bills.” The reality is more nuanced. Windows account for 25–30% of a home’s heat loss, and replacing single-pane windows with high-performance double or triple-pane units does meaningfully reduce that loss. But replacing old double-pane windows with new double-pane windows of similar performance may save relatively little.

Ask the contractor to give you a realistic estimate of energy savings based on: your current window type and condition, the proposed replacement’s U-factor, and your home’s approximate heating load.

A realistic answer: “For your home’s size and your current windows, you can expect annual savings of approximately $X–$Y on heating costs” — with a specific number, not a vague percentage.

What is the payback period for this investment?

Divide the net cost of window replacement by the estimated annual energy savings. A realistic payback period for window replacement is often 15–30 years for the energy component alone — much longer than many sales pitches imply. The honest answer acknowledges this and positions the investment appropriately.

Questions About Condensation

Will these windows reduce condensation compared to what I have now?

Condensation on the interior surface of a window indicates the interior glass surface is colder than the dew point of the interior air. Higher-performance windows — lower U-factor, warm-edge spacers, triple-pane — have warmer interior glass surfaces and are significantly less prone to condensation.

Ask specifically what the condensation resistance factor (CRF) is for the proposed windows, and whether it’s meaningfully better than your current windows.

Related Questions

• Questions to Ask a Window and Door Contractor Before You Hire One
• Questions to Ask a Window and Door Contractor About Products and Materials
• Do New Windows Actually Save Energy?
• How Much Do New Windows Cost ?

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