Low-Load Efficient Heat Pump Investigation: 2023 – 2025 Summary Report

The Northwest Energy Efficiency Alliance’s (NEEA) Advanced Heat Pump program is working to transform the market for high efficiency residential heat pumps. A key focus for the program is improving product differentiation so consumers and industry professionals can easily identify systems that deliver cost-effective performance to make more informed purchase decisions. One important differentiator the program is investigating is the low-load efficiency of variable speed heat pumps, which is defined as the rated coefficient of performance when operating at minimum capacity and outdoor temperatures around 47 degrees Fahrenheit. How well variable speed heat pumps can operate under low-load conditions is critical because heat pumps that operate efficiently under these conditions can reduce energy use and improve comfort, all while maintaining affordability.

Between 2020 and 2025, NEEA co-funded multiple research investigations in partnership with the Northeast Energy Efficiency Partnerships (NEEP) to understand and verify low-load efficiency in variable speed heat pumps. This report summarizes those investigations, provides evidence of the value and market potential for heat pumps that operate more efficiently under low-load conditions, and highlights opportunities for manufacturers and consumers alike to benefit from better-performing systems.