Dry
Dry heating systems are normally electrical - though there are electric storage systems, which do heat hot water and circulate this around pipework. The most common form of 'dry' central heating is the storage unit. This runs off cheap rate electricity - usually at night when demand is at its lowest - and heats up refractory blocks with electric elements. These in effect are electric radiators: the heat stored in them at night is emitted throughout the day, but they can also be switched over to 'full-price' electricity if extra heat is required.
Some of these storage units are fan assisted, but they do not provide instantaneous heat. A ducted system - which can be operated by any kind of heating source - is where the heat exchange occurs by air circulation and fan assistance through electrically heated elements, out through grills with circulating hot water. Ducts or 'registers' of different sizes are placed in rooms to provide the heat. Ducted systems are normally installed as the house is constructed because of the ducting needed to circulate the warm air throughout the house.
