A heat pump is a machine or device that moves heat from one location (the 'source') at a lower temperature to another location (the 'sink' or 'heat sink') at a higher temperature using mechanical work or a high-temperature heat source.
A device that transfers heat from a colder area to a hotter area by using mechanical energy, as in a refrigerator
apparatus that extracts heat from a liquid that is at a higher temperature than its surroundings; can be used to transfer heat from a reservoir outside in order to heat a building
A device which uses compression and decompression of gas to heat and/or cool a house.
Duct Heater
Loft mounted Systemair duct heater fitteded in the supply line from the ventilation system. Plumbed to recieve water from the towel rail circuit when demanded by thermostat to prewarm air in the ventilation system during very cold weather.
Heater
I've been seeing a lot of these recently. The combustion takes place outdoors, and hot glycol is pumped through hoses indoors to heat exchangers.