Glossary · Insulation & windows

Energy Rating (ER) for windows

Also called: ER rating · window energy rating · ER number · ER 34

A Canadian window score that balances heat loss against free solar heat; higher is better, and ENERGY STAR Canada accepts ER 34 or more.

What it means

The ER is a unitless number based on a window's U-factor and its solar heat gain (SHGC) under typical Canadian heating conditions. Because it credits solar gain, two windows with the same U-factor can have different ERs. It's most useful for comparing windows in heating-dominated climates.

Why it matters in an audit

ER is one of two ways a window can qualify for ENERGY STAR Canada, and rebates such as Ontario's HRSP require ENERGY STAR certified windows.

Typical numbers

Reference values with their sources. Your energy advisor’s report gives the figure for your own house.

What	Value	Source
ENERGY STAR Canada (Version 5.0)	ER 34 or more, as an alternative to a U-factor of 1.22 W/m²·K or less	natural-resources.canada.ca ↗
Ontario HRSP windows and doors rebate	$100 per rough opening, ENERGY STAR certified (assessment stream)	saveonenergy.ca ↗

Sources

Learn more here

Windows and doors →

Related terms

U-factor (U-value) How fast heat passes through a window, door or wall assembly; lower is better, the opposite of R-value.
Solar heat gain coefficient (SHGC) The share of the sun's heat a window lets into the house, from 0 to 1; lower keeps homes cooler, higher adds free winter heat.
Low-e glass Window glass with a thin, invisible metal coating that reflects heat, keeping more warmth in during winter and out in summer.
ENERGY STAR The government-backed blue label for products and some homes that beat minimum efficiency standards by meeting stricter criteria.
Ontario Home Renovation Savings Program (HRSP) Ontario's home rebate program, run by Enbridge Gas and the province's Save on Energy, for insulation, windows, air sealing, heat pumps and more.

← Every term, A to Z