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FGIA: One country, two pathways

“Industry associations are collaborating on a white paper on thermal performance compliance pathways in fenestration.”

June 4, 2021  By Amy Roberts

There are two pathways to calculate fenestration thermal performance in Canada: the U-factor pathway and the Energy Rating pathway. U-factor is a physical measurement of the amount of heat energy transferred across a unit area of wall over a given time span per degree of indoor-outdoor temperature difference. ER is a dimensionless rating number arrived at by calculation and computer modeling that combines and demonstrates the balance among solar heat gain, U-factor and air infiltration. The higher the number, the more efficient the product. For most Energy Star-approved windows, ER ranges between 25 and 35 points. Note that fixed windows will naturally have a higher ER number than operable windows and only like operator types can be meaningfully compared using ER ratings. The two indices cannot be directly translated from one to the other.

There is some confusion in the Canadian marketplace as to when to use one or the other of these two compliance pathways to demonstrate energy efficiency – not just for architects, specifiers, building officials and homeowners, but also within the fenestration industry itself. This has been an ongoing issue for well over 10 years and was recently a subject of discussion at the Natural Resources Canada Market Transformation Roadmap meetings. 

The time has come to provide clarification to the Canadian market as to what these two values mean, the appropriate use of either of these values and which jurisdictions accept them. To bring this about, the Canadian fenestration industry, as represented by FGIA, the AVFQ, the Fenestration Association of BC, Fenestration Canada, and Fenestration Manitoba, have launched a collaborative effort to develop a substantive white paper document for end-users that provides a clear understanding of the two compliance pathways for thermal performance of fenestration for both residential and commercial buildings in Canada. Provisionally titled Thermal Performance Compliance for Fenestration in Canada, it will provide information on fenestration product compliance for thermal performance in Canada for architects, homeowners, building code officials and other interested stakeholders. 

To be presented in a neutral and non-preferential format, the finished document will be comprised of historical background information, details about the two different U-factor and Energy Rating calculation variables and what they represent, examples of the appropriate application and the rationale behind each thermal performance rating pathway, and it will define the considerations for using each. It will additionally include an interpretation of the associated product labels, information on which jurisdictions accept one or both thermal performance compliance pathways as prescriptive and/or performance-based approaches and supply a list of resources and references for further information.


The committee preparing this document includes coast-to-coast representation from top experts in the field. For example, in order to ensure consistency with the CSA A440.2 technical specification, the chair and co-chair of the CSA A440.2 committee are at the table. Also, the committee includes participation from NRCan and a representative building inspector from the township of Rothesay, N.B. Others could contribute as the project progresses. The first meeting of the group took place on April 8 with a detailed examination of the document’s outline and content.   

It is important that all industry organizations and representation from across Canada come together to develop this much-needed education piece, which everyone will be able to post to their website as a complimentary download. All collaborating parties will be equally acknowledged for their contribution.

Amy Roberts, FGIA director of  Canadian and technical glass operations

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