How to Select a Pump Group by Boiler Output and ΔT

A pump group is selected not by pipe diameter but by the calculated flow rate of the heat-transfer fluid. The formula is straightforward: **G = Q / (1.16 × ΔT)**, where G is the flow rate (m³/h), Q is the circuit output (kW), and ΔT is the temperature difference between supply and return (°C). **Example** Radiator circuit of 24 kW, ΔT = 20 °C: G = 24 / (1.16 × 20) ≈ 1.03 m³/h. For [underfloor heating](/catalog/kolektory-pidloha), ΔT = 5–7 °C is used, so the flow rate for the same output will be approximately three times higher. **Common Mistakes** - Using ΔT = 20 for underfloor heating — the pump delivers insufficient flow and remote loops stay cold. - Installing an oversized pump »with margin« — noise, cavitation, unnecessary power consumption. - Ignoring the hydraulic resistance of the circuit (head) — the pump never reaches its operating point. **How Termojet Solves This** [Termojet pump groups](/catalog/nasosni-hrupy) feature a built-in balancing valve that allows precise adjustment to the calculated flow rate after installation. And the energy-saving [APM/APE](/catalog/nasosy) pumps with electronic control automatically maintain optimal speed, saving electricity. Select your group by flow rate and head, not by habit — and your system will run quietly, evenly, and efficiently.