**Required heating capacity and required temperature differential of the medium are relevant when calculating the design water flow rate for a heating system.**

The following parameters are relevant when calculating the design water flow rate for a heating system:

- required heating capacity

- required temperature differential of the medium.

The water flow rate qv corresponding to a given heating output Φ is calculated from the formula:

qv = Φ/Dtx cv x ςv) [m³/s]

where:

Φ= heating output [kW]

Dt= difference between supply and return temperature of the water [K]

cv= specific heat capacity of water[kJ/kg K]

ςv= density of water [kg/m³]

The required water flow rate compared with the maximum acceptable flow velocity and the pressure loss in the system is used to define the sizes of piping, pumps, valves and other components.

Water flow rate and temperature are the two parameters used to regulate a heating system, to achieve the required heating output.