Typically, air-source heat pumps (ASHPs) are unattractive as a heat source in cold climates. Several design modifications and technologies have been recently proposed or introduced (alone and in combination) for cold-climate heat pumps and, within the last five years, at least two U.S. companies have designed ASHPs for cold climates. This month’s Emerging Technologies discusses the reliability of these new designs and the potential for primary energy savings.