When homeowners compare replacement windows, the conversation often sounds like this:

“This one has Low-E.”

“This one is triple glazed.”

“This one is more energy efficient.”

But how do you actually compare them?

In Canada, window performance can be evaluated using several standardized metrics.

Three of the most important are:

• U-factor
• Energy Rating (ER)
• Solar Heat Gain Coefficient (SHGC)

Natural Resources Canada uses these values when describing the energy performance of windows, doors and skylights.

Understanding them makes window shopping much easier.

What Is U-Factor?

U-factor measures the rate of heat transfer through the complete window.

For homeowners, the rule is straightforward:

Lower U-factor = less heat transfer.

NRCan specifically states that a lower U-factor represents better insulating performance.

This matters during an Ontario winter because you want to reduce unwanted heat movement through the window assembly.

What Is Energy Rating?

Energy Rating—or ER—combines several factors into one number.

It considers:

• U-factor
• Solar heat gain
• Air leakage

NRCan describes ER as a balance of those three performance factors.

For ER:

Higher is better.

This gives homeowners a broader comparison than looking at glass insulation alone.

What Is SHGC?

SHGC stands for Solar Heat Gain Coefficient.

It describes how much solar heat enters through the window.

Higher SHGC means more solar heat enters.

Lower means less.

Neither is automatically “best.”

For example, significant solar gain may be useful on one orientation during winter but contribute to overheating on another.

NRCan specifically cautions that very high SHGC on large south- or west-facing glass areas can increase summer overheating and cooling demand.

Why Pane Count Alone Isn’t Enough

Triple glazing can improve thermal performance.

But you still need to compare:

• Glass coatings
• Gas fill
• Spacer
• Frame
• Air leakage
• Complete certified rating

A high-quality double-glazed window can sometimes perform competitively with a weaker triple-glazed configuration.

That is why you should compare the numbers, not just the pane count.

What Does ENERGY STAR Canada Require?

Current ENERGY STAR Canada criteria allow qualifying residential windows and doors to meet performance through either maximum U-factor or minimum ER requirements.

Rather than memorizing every specification, homeowners should ask contractors to show the actual certified rating for the proposed unit.

Envirotech currently offers Regency replacement windows with different glass configurations, including Low-E, argon and double- or triple-glazed options.

Don’t Buy “Energy Efficient.” Buy Measured Performance.

Before comparing prices, compare:

U-factor. ER. SHGC. Air leakage. Glass package. Installation.

Envirotech Exteriors can help you select a window configuration based on the actual performance requirements of your home—not simply the biggest number on a brochure.