Modern air-source heat pumps (as opposed to those using a buried underground heat source/sink) running on grid electricity generated from natural gas can deliver up to twice the space heating as burning the gas locally in a high-efficiency furnace. The performance of heat pumps falls with temperature, however, and below a certain temperature (around −20° C), they become ineffective. While heat pumps have been widely adopted in mild climates, have the latest generation become efficient enough that they are a viable choice for locations with cold winters?