Lower is better
U-value
How fast heat escapes, in W/m²K. The headline figure. Always ask whether it is the whole window or just the glass — the glass-only number is always flattering and always irrelevant.
Home / Technical
Technical
The numbers,
and what they mean.
Everything on this page is a figure you can check. Where we do not yet have certified test data, we say so rather than rounding a marketing number into a technical one.
The four numbers that describe a window
Depends on orientation
SHGC
How much solar heat gets in. High is a gift on a south wall in January and a liability on a west wall in July. There is no single correct value — only a correct value for that elevation.
Lower is better
Air infiltration
How much cold air comes through the gaps. This is the number you actually feel, and the number almost nobody publishes.
Higher is better
Water and structural
The pressure the unit holds before water gets past the seal or the frame deflects. Matters most on a tall or exposed elevation.
The glazing build-up
A triple-glazed unit is not simply three sheets of glass. Reading it from outside in: a pane, a sealed cavity of argon, a middle pane, a second argon cavity, and an inner pane carrying a low-emissivity coating that reflects long-wave heat back into the room instead of letting it radiate out through the glass.
Around the perimeter, holding the panes apart, sits the spacer. Get this wrong and everything upstream is wasted. An aluminium spacer conducts heat straight around the edge of the unit — which is precisely where condensation appears on a cold morning. A warm-edge spacer interrupts that path. It is a small, cheap component with an outsized effect, and it is the first thing a low-cost window quietly leaves out.
Compliance
Ontario Building Code
Housing glazing performance is governed by Supplementary Standard SB-12, and the required U-value depends on the compliance package and the heating system. We publish the current requirement and its amendment date here rather than a number that may already be stale.
ENERGY STAR
Certification status, certificate number and climate zone will be published here — verifiable in one click. We are not putting an unverifiable badge on this website.
Passive House
Component certification status for the 92 mm system will be published here with the certificate. Until it is, we do not claim it.
Placeholders on this page are deliberate and visible. A fabricated performance figure is the one lie in this industry that ends a company, and we would rather ship an honest gap than a confident invention.
Common questions
What is a U-value, and how is it different from an R-value?
A U-value measures how fast heat escapes. An R-value measures how well something resists heat escaping. They are reciprocals: U = 1/R. Insulation is sold in R-values, where higher is better. Windows are specified in U-values, where lower is better. A whole-window U-value of 0.9 W/m²K is a good triple-glazed unit. Anything above 1.6 is a window you will feel in January.
What U-value does the Ontario Building Code require for windows?
Ontario's prescriptive path for housing is set out in Supplementary Standard SB-12, and the required maximum U-value depends on the compliance package you build to and the heating system in the house — packages with a heat pump allow different glazing than packages with a gas furnace. Because SB-12 is amended periodically, we publish the current requirement and the amendment date on this page rather than quoting a number that may be out of date by the time you read it.
What is the difference between argon and krypton fill?
Both are inert gases that conduct heat more slowly than air. Krypton performs better in a narrow cavity, which matters when you are fitting three panes into a limited frame depth. It also costs considerably more. Argon is the right answer for almost every project; krypton earns its cost only in a Passive House assembly.
What is a warm-edge spacer?
The spacer is the strip that holds the panes apart at the perimeter of the glass unit. Traditional aluminium spacers conduct heat straight around the edge of the glass — which is exactly where you get condensation on a cold morning. A warm-edge spacer is a low-conductivity polymer or stainless composite that interrupts that path. It is a small component that has a disproportionate effect on the edge of the glass, and it is the first thing a cheap window omits.
What is air infiltration and why does it matter more than the U-value?
The U-value tells you how fast heat conducts through the window. Air infiltration tells you how much cold air comes straight through the gaps around the sash. In a real house, on a windy night, the second number is what you actually feel at the sill — and it is the number almost nobody publishes. Ask for it. If a supplier will not give you an air infiltration figure, that is the answer.
Need the full data set?
Test reports, U-value tables, CAD details and Revit families are on the architects page. Ungated — no form, no email address, no sales call.
Open the detail libraryinfo@ruhle.ca