Window ratings explained: NFRC, ENERGY STAR and NAFS

Four ratings, four questions

• NFRC rates heat loss (U-factor), solar heat gain (SHGC) and daylight (VT). These three are the required ratings on an NFRC label.
• ENERGY STAR in Canada is a pass mark set by Natural Resources Canada, using the U-factor or an Energy Rating, plus an air leakage limit.
• NAFS (the North American Fenestration Standard, with its Canadian supplement) rates how a window stands up to wind load, water and air leakage. It is written as a class and a grade, such as AW-PG90.
• Passive House certification is a separate component certificate from the Passive House Institute. Read how to check a Passive House certificate.

NFRC itself doesn’t set a pass or fail level: in the US EPA’s words, it “does not distinguish between ‘good’ and ‘bad’ windows.” ENERGY STAR is the program that sets one. See ENERGY STAR on NFRC ratings.

Read the NFRC numbers

U-factor measures how well a window keeps heat in; lower is better. SHGC is the share of the sun’s heat that gets through; lower keeps more heat out and higher lets more in. VT is the share of visible light that gets through; higher means more daylight. SHGC and VT are ratios between 0 and 1. See NFRC’s definitions.

U-factor is given in W/m²K or in Btu/h·ft²·°F, and Innotech’s sheets list both. To convert, multiply the US figure by 5.678263: 0.14 Btu/h·ft²·°F is about 0.79 W/m²K. See the conversion in the ENERGY STAR Canada specification.

Check that a figure covers the whole window. NFRC’s U-factor combines the glass, its edges and the frame. A centre-of-glass value, as Natural Resources Canada explains, covers only the glass, so it can’t be compared with a whole-window figure. See NRCan’s rating terms.

NFRC rates each product type at one model size. Fixed and tilt-and-turn windows are both rated at 1200 × 1500 mm (47 × 59 in), and Innotech’s NFRC sheets use that tested size. See NFRC 100, Table 4-3. These are the ranges on Innotech’s sheets across the glass options each one lists:

Each range covers the glass combinations on the sheet, which differ in low-E coating and glass thickness. Innotech says NFRC values for other glass combinations are available on request. See the 76TS NFRC sheet (its file name is dated 2022-07-26). See the 88PH+ Pro and XI NFRC sheet.

Innotech’s product pages give slightly different ranges from the sheets. The 76TS page, for example, lists 0.86–1.14 W/m²K for a triple-glazed fixed window. See the 76TS product page. When two documents differ, ask for the sheet value for your exact glass.

ENERGY STAR in Canada

Canada’s ENERGY STAR specification for windows and doors is Version 5.0, in effect since 1 January 2020. To qualify, a window or door needs either:

• a U-factor of 1.22 W/m²K (0.21 Btu/h·ft²·°F) or lower; or
• an Energy Rating (ER) of 34 or higher.

It also needs air leakage of 1.5 L/s/m² or less, both in and out. ER is a single number that balances heat loss, air leakage and solar gain; higher is better. Read the ENERGY STAR Canada specification.

A figure under the limit is not a certification. ENERGY STAR applies to a certified model, so ask for the certification record of the model you are ordering. The specification also says NAFS certification isn’t required for ENERGY STAR, so one doesn’t stand in for the other. For rebates tied to ENERGY STAR, see the Ontario rebate guide.

Read a NAFS rating

A NAFS rating such as AW-PG90 has two parts. The letters are the performance class, which describes the kind of building the window is meant for:

• R: one- and two-family homes.
• LC: low- and mid-rise multi-family buildings, with larger sizes and higher loads.
• CW: low- and mid-rise buildings with larger sizes, higher loads, deflection limits and heavy use.
• AW: high- and mid-rise buildings, with higher loads, deflection limits and frequent, extreme use.

The number after PG is the performance grade. A window gets a grade only after it passes all the applicable tests, mainly structural load from wind, water penetration and air leakage. See FGIA’s NAFS questions and answers. In Canada, the water test pressure is capped at 720 Pa (15 psf). See FGIA’s performance class overview. The Canadian supplement to NAFS, CSA A440S1, gives the method for working out the minimum water, wind and snow load performance for a building’s location. See CSA A440S1. Your designer or window supplier uses it to set the minimum for your project.

The grade belongs to the size that was tested. A larger window of the same system can rate a lower class and grade. Innotech says its headline grades are based on the tested sizes. These rows are from its summaries:

The 88PH+ summary covers both the 88PH+ Pro and XI. Innotech says other tests have been run, so ask for the result closest to your window’s size and type. Read the 76TS window NAFS summary. Read the 88PH+ window NAFS summary.

Compare quotes like for like

• The same rating in the same units: W/m²K against W/m²K.
• A whole-window value, not centre-of-glass.
• The NFRC tested size, and the glass you are actually ordering.
• A NAFS row whose tested size and type are close to your window.
• The ENERGY STAR certification record for the model, if a rebate depends on it.
• Passive House values compared only with other Passive House values. PHI calculates its Uw at a different size, 1.23 × 1.48 m, under its own rules. The 88PH+ XI fixed window, for example, has a PHI Uw of 0.59 W/m²K and an NFRC U-factor of 0.74–0.80 W/m²K.

Haven’s performance page summarises Innotech’s published ratings. The technical library holds the full sheets, and the quote checklist lists what else to compare.