Aug 29, 2023

Case Study: Designing for Electrification: Pairing a Cold Climate Heat Pump with an Efficient Gas Furnace

Project Background 

Beginning in August 2022, CEE, MN ASHP Collaborative, and TCHFH developed a plan for energy modeling and HVAC system design of a new home. While TCHFH consistently builds airtight homes, they had not yet incorporated ASHPs into their home designs. Based on TCHFH’s interest in building energy efficient homes, CEE helped familiarize TCHFH with ASHPs and identified scenarios where they could use ASHPS to electrify and decarbonize their homes.

This case study highlights how an ASHP can effectively pair with a 96% efficient ducted gas furnace to increase heating efficiency, while adding a source of efficient cooling. In this dual fuel setup, an ASHP, which is more efficient than a natural gas furnace, can be used as the primary heating and cooling system throughout most of the year. These gains in efficiency and electrification are projected to provide substantial energy savings and opportunities for decarbonization. 

Case Summary

House Details 

  • Where: Minneapolis, MN 

  • Built: 2023 

  • Size: 2240 ft2 

  • Number of Bedrooms: 5 

  • House Type: Two-story 

Energy Profile 

  • Primary Heating System: Dual Fuel Heat Pump: 2.5 tons, variable-speed, 16.6 SEER2, 8.2 HSPF2, 1.99 rated COP @ 5°F 

  • Capacity Balance Point: 9°F 

  • Heating Design Load: 25.4k Btu/hour (at -11°F) 

  • Cooling Design Load: 12.32k Btu/hour (at 89°F) 

  • Secondary Heating System: 96% efficient natural gas furnace (switch over at 35°F) 

  • Window Efficiency: U-Value: 0.3, SHGC: 0.31 

  • Energy Efficient Lighting: 100% 

  • Water Heating: Residential Water Heater • Natural Gas • 0.72 UEF 

  • House Tightness: 457 CFM50 (or 1.22 ACH50) 

  • Ventilation: 74 CFM • 39 Watts • HRV 

  • Duct Leakage to Outside: 16 CFM @ 25Pa (0.63 / 100ft2) 

  • Insulation: R50 (attic), R24 (sidewalls), and R10 (foundation and slab) 

Certifications and Savings 

  • HERS Model Score: 16 (projected with solar) vs. 45 (projected without solar) 

  • ZERH Target Score: 53 

  • Annual Savings Projected: $526 (relative to average new home constructed to MN code requirements) 

  • Certifications: Energy Star, Indoor airPLUS, Zero Energy Ready Home 

  • Utility Rebates: $500–$800 for ASHP and $500 for heat pump water heater dependent on HSPF rating and quality installation by a registered contractor