Design flow temperature

Design flow temperature is the heating-water temperature a heat pump, boiler or heat network design assumes will leave the heat source at the chosen cold-weather design condition. In heat pump work it appears in heat loss calculations, emitter schedules and MCS design information because emitter output and heat pump efficiency both depend on the chosen flow temperature. A lower design flow temperature can improve heat pump efficiency, but only if the radiators, underfloor heating or fan convectors can still meet the room heat losses. It is not the live flow temperature on every day, the return temperature, the hot water cylinder temperature, a room thermostat setting or proof that the heating design is correct.