Due to the efficiency of compressors, heat pumps are typically thought to be much more
efficient than electric furnaces. However, duct losses can largely compromise this higher efficiency.
Because heat pumps operating in compressor mode supply air at a lower temperature than furnaces,
duct losses are a greater fraction of the heat supplied by the heat pump that goes toward satisfying the
heating load compared to the same duct losses with a furnace. Further, since duct losses make it more
difficult for the heat pump to heat the house, there will also be an increase of the use of backup
resistance heat for which there is no compressor efficiency benefit. The result can be that the iinancial
cost from duct losses in heat pumps is comparable to that from furnaces, despite the advantage of
This paper presents the results of a series of calculations of duct efficiency using the bin method
combined with a duct efficiency model developed at Ecotope. Six climates in the Northwest United
States are chosen, with hourly heating season temperatures divided into five degree Fahrenheit bins.
The impacts of various combinations of air leakage and conduction losses from the ducts are calculated
for an electric furnace and a heat pump. The resulting system and duct distribution efficiencies are
compared among different loss scenarios and between the different air handlers, and the economic
costs of the losses are quantified.