Another improvement in heat pump technology is that the scroll compressor, which is made up of 2 spiral-shaped scrolls. One remains stationary, while the other orbits around it, squeezing the refrigerant by forcing it into progressively smaller regions. Compared to the normal piston compressors, scroll compressors have a longer working life and are quieter. According to some reports, heat pumps with scroll compressors supply 10° to 15°F (5.6° to 8.3°C) warmer air when in the heating mode, in comparison to existing heat pumps using piston compressors.
Even though most heat pumps use electric resistance heaters as a backup for cold weather, heat pumps are also equipped with burners to supplement the heat pump. Back-up burners help resolve the issue of the heat pump providing relatively cool air during cold weather and reduces its use of power. There are not very many heat pump manufacturers that incorporate both kinds of heat supply in 1 box, so these configurations are usually two smaller, side-by-side, standard systems sharing the same ductwork. The combustion fuel half of this system might be propane, natural gas, oil, as well as coal and timber.
As compared with a combustion fuel-fired furnace or standard heating pump, this sort of system is also inexpensive. Actual energy savings are determined by the relative prices of the combustion fuel relative to power.