The temperature of the Heating circuit water flowing to a radiator. As a rule, the Flow temperature
in radiator heating systems is up to 70 °C (up to 40 °C in underfloor heating systems). The temperatures are only that high, however, when outside temperatures are low. If the outside temperature increases, then the flow temperatures decreases.
Flow temperature
Fuels
Fuel oil, natural gas, LPG, and biogas are all used as Fuels
and are essentially hydrocarbon chains. Their energy content is released when they are mixed with air and combusted.