Estimate pump duty, indicative pump type, hydraulic power, electrical input,
annual energy, running cost and carbon impact for hydronic systems.
For design guidance only. Always verify with a qualified engineer and manufacturer curves.
About this pump selection calculator
This free pump selection calculator estimates the required pump duty, flow rate and head, for hydronic building-services systems, then works out indicative pump type, hydraulic power, electrical input, annual energy, running cost and carbon impact. It is built for UK building-services engineers, M&E contractors and design teams sizing circulators and commercial pumps for LTHW heating, chilled water, condenser water, secondary and primary heating, DHW circulation and general hydronic duties. Flow can be entered directly or derived from a heating or cooling load.
How it works
Hydraulic power is calculated as P = ρ·g·Q·H, where ρ is fluid density, g is gravitational acceleration (9.81 m/s²), Q is volumetric flow and H is head. When flow is taken from load, Q is found from the load divided by the fluid specific heat capacity and temperature difference. Electrical input is hydraulic power divided by a wire-to-water efficiency (40%, 55% or 70%), and annual energy, cost and carbon follow from your operating hours, electricity rate and carbon factor (UK grid default 0.207 kgCO₂e/kWh). Indicative pump-family bands and design defaults align with CIBSE Guide B1 and BSRIA BG 12; fluid properties reference CIBSE Guide C and ASHRAE Handbook Fundamentals.
Frequently asked questions
Can I size from a heat load instead of a known flow?
Yes. Toggle “Calculate flow from heat load” and enter the heating or cooling load in kW with a temperature difference ΔT. The calculator uses the selected fluid’s specific heat capacity and density to derive flow, with a default ΔT per system type that you can override.
Does it account for glycol and operating temperature?
It applies nominal specific heat and density values for water and 20–40% glycol, and flags when the operating temperature falls outside the typical range for your system type, including a Legionella warning for DHW below 55°C.
Is this a final pump selection?
No. It is preliminary engineering guidance for early sizing and energy comparison. The indicative pump type is a coarse decision tree, so final selection must be checked against manufacturer pump curves, the project specification, control strategy and commissioning requirements.