Matching a circulator to its Q–H duty point is necessary, but not sufficient. A poorly chosen control mode may waste electricity, create valve noise or deprive remote heating circuits of flow even when the pump itself is correctly sized. The objective is to select a hydraulic strategy and verify the result at partial load.
Three strategies that should not be confused
A fixed-speed or constant-curve pump follows a selected speed curve as demand changes. Constant differential pressure (Δp-c) control attempts to maintain a chosen pressure difference. Proportional differential pressure (Δp-v) reduces the pressure setpoint as flow demand falls. Variable-speed capability is therefore not synonymous with proportional-pressure functionality.
The published ATLAS VFPUMP page lists an integrated frequency converter, constant-flow and constant-pressure modes, and automatic adaptation. It does not establish that every VFPUMP variant offers a dedicated Δp-v setting. Verify the available menu functions against the exact model and its current manual.
Radiators versus underfloor heating
In systems with thermostatic radiator valves, closing valves reduce flow and distribution-pipe friction losses. Where hydraulically appropriate, a proportional-pressure strategy can avoid maintaining excessive differential pressure at the valves and reduce noise. It is not an unconditional recommendation: riser lengths, minimum heat-source flow and separate differential-pressure regulators matter.
Constant differential pressure is often a useful starting point for manifold-based underfloor heating, where stable loop supply is desirable. Mixing assemblies, zone actuators, bypass paths and source-side minimum flow may change the preferred setting. Use manufacturers’ application notes as guidance, not as a substitute for hydraulic calculations.
What does four metres of pump head mean in a closed loop?
In a filled, closed hydronic circuit, the pump normally overcomes the friction losses of pipes, fittings, coils and valves rather than continuously lifting water through the building height. One metre of water head corresponds to approximately 9.81 kPa. A circuit requiring 4 m at its design flow therefore needs about 39.2 kPa differential pressure. Check that operating point on the pump curve; do not infer it from Hmax alone.
Worked example: calculate kWh rather than repeating a savings claim
Consider two illustrative operating conditions with measured-average input powers of 65 W and 35 W, each running 2,000 hours per year. E₁ = 65 × 2,000 / 1,000 = 130 kWh; E₂ = 35 × 2,000 / 1,000 = 70 kWh. The difference is 60 kWh/year, or 46.2% in this hypothetical scenario. These are not ATLAS product test results or a guaranteed savings percentage.
A valid field comparison holds delivered comfort and system service constant. Record operating hours, input power, critical-circuit temperatures, valve behavior and, where possible, flow and differential pressure. Electricity tariffs affect cost savings, not the energy difference in kWh.
Six commissioning checks
Calculate design flow and circuit pressure loss; do not select by Qmax or Hmax alone. Confirm the modes actually supported by the installed hardware and firmware. Balance radiators or manifold circuits at their design flows. Test comfort and temperatures at the hydraulically critical endpoint under partial load. Investigate noise and low-flow symptoms as thermostatic valves close. Record before-and-after electrical energy under comparable operating conditions.
How this relates to ATLAS VFPUMP
A useful enquiry contains the Q–H duty point, heating emitter type, valve operating pattern, heat-source minimum flow and desired control strategy. ATLAS VFPUMP should be assessed using the latest data for the selected variant, not by extrapolating features from a generic description of smart pumps.
Review the ATLAS VFPUMP product range and request a model-specific selection using your Q–H duty point and control requirements.
Figures are engineering examples. Savings, control functions and certifications require variant-specific verification.
Related products and technical guides
ATLAS VFPUMP circulation pumps