Case Study: Retrofitting for Electrification: Pairing a Cold Climate Heat Pump with an Existing Gas Furnace

Project Background 

Beginning in August 2022, CEE, MN ASHP Collaborative, and Twin Cities Habitat for Humanity (TCHFH) developed a plan for energy modeling and HVAC system design of an existing home. Based on TCHFH’s interest in retrofitting existing homes with ASHPs, CEE helped familiarize TCHFH with heat pumps and identified scenarios where they could use ASHPs to electrify and decarbonize their existing homes.

This case study shows how an electric ASHP can pair well with an existing natural gas furnace to increase heating efficiency, while also adding a source of efficient cooling. While TCHFH consistently builds and retrofits homes for efficiency and airtightness, they had not yet incorporated ASHPs into their home designs. Since the home highlighted in this study was relatively airtight, the heating and cooling systems could be more easily optimized for energy efficiency.

By performing in-depth analysis and testing of this TCHFH home, we were able to understand the up-front costs and ongoing operational costs of pairing an electric ccASHP with an existing natural gas furnace. In this dual fuel setup, a ccASHP can be used as the primary heating and cooling system throughout the year. Because ASHPs are much more energy efficient than natural gas furnaces, they can be used for heating on all but a few of the coldest days of the year. These gains in efficiency and electrification will result in substantial energy savings and opportunities for decarbonization.