Mechanical
Flow Rate Calculator
Calculate heating water flow rate from heat load and design temperature difference.
Use this calculator for quick heating flow checks where heat load and design temperature difference are known. Based on standard building services engineering relationships commonly used in UK practice.
Inputs
Result
Flow Rate
-
Enter values and click calculate.
Method
The heating flow rate is derived from the standard heat transfer relationship:
Q = ṁ × Cp × ΔT
Rearranged for volumetric water flow rate:
Flow Rate (L/s) = Heat Load (kW) ÷ (4.18 × ΔT)
- Q = heat load (kW)
- Cp = specific heat capacity of water, taken as 4.18 kJ/kg·K
- ΔT = temperature difference between flow and return water (°C)
- Calculated flow rate = -
Reference
- Typical calculation method used in heating water system design.
- Commonly aligned with standard building services engineering practice and CIBSE-based heating design methodology.
- Relevant references may include CIBSE Guide B and CIBSE Guide C for heating and pipework design principles.
Design note: This calculator provides indicative results only. Final system design should consider pipe sizing, velocity, pressure loss, pump head, control strategy, diversity, water properties, and project-specific design criteria.