How a heat pump is sized and programmed strongly affects its performance over its lifetime. Sizing it correctly can increase energy and emissions savings, reduce operating costs, and improve customer satisfaction. Current industry practices, often relying on outdated rules of thumb or overly conservative models, can result in oversized systems that compromise performance, increase costs, and erode public trust. Additionally, hybrid heat pumps may be programmed in ways that fail to optimize the use of the more efficient and lower-carbon heat pumps.
To support installers, this report recommends developing and promoting tools that encourage the use of modern, best-in-class industry practices: using historical heating energy use for sizing and improving hybrid system programming. Along with requirements in incentive programs and complementary policies, these practices can help ensure that heat pumps fulfill their promise as a dependable, comfortable, and cost-effective technology for Canadian homeowners.
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Modern Tech, Modern Practices
Upgrading Heat Pump Sizing Guidelines in Canada
September, 2025
By Heather McDiarmid, Mathieu Lévesque
About the Author
Heather McDiarmid
Founder
Heather McDiarmid is the founder of McDiarmid Climate Consulting, which specializes in research, analysis and communications work related to decarbonizing the residential sector. Recent work includes modeling the cost effectiveness of heat pumps in Ontario and the impact of widespread heat pump adoption on the Ontario grid. She has also developed climate-related course materials for educational and corporate institutions including the International Civil Aviation Organization and holds a Research Associate position at the University of Waterloo. When not working to build a climate-safe future, she enjoys hanging out with her family, biking, kayaking, and playing the oboe.
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Mathieu Lévesque
Technologies & Alternatives Lead, Building Decarbonization Alliance
Mathieu bridges technical expertise and policy strategy, backed by 15 years in both applied decarbonization and clean energy consulting. He has advised governments, utilities, industry groups and property owners on initiatives ranging from building-level projects to sector-wide assessments and strategies across North America. Previously, he was a Managing Consultant at Dunsky Energy + Climate Advisors where he acted as the firm’s heating decarbonization lead, and was an efficiency engineer before that. Mathieu holds a master’s in mechanical engineering from Polytechnique Montréal and an MBA from HEC Montréal and is a registered Professional Engineer in Québec.
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