Term
Flow temperature: what the term means
The temperature of the water a boiler or heat pump sends to the radiators or underfloor heating.
The temperature of the water a boiler or heat pump sends to the radiators or underfloor heating.
Flow temperature in practice
The flow temperature is how hot the water leaving the heat source is. Traditional gas systems were often set high, which lets small radiators heat a room quickly. Heat pumps work most efficiently at lower flow temperatures, so a heat pump design usually aims for the lowest temperature that still keeps each room warm on a cold day.
That target decides radiator sizes. A room-by-room heat loss calculation shows how much heat each room needs; the installer then checks whether the existing radiator can deliver it at the design flow temperature, and upsizes it if not. Lowering a gas boiler's flow temperature can also improve its efficiency in some homes.
Source: legislation.gov.uk · mcscertified.com