Radiator Balancing Wizard

V̇ = φ/(ρ·c_p·ΔT), where φ is the radiator's required heat output, ρ is water density (≈1000 kg/m³), c_p is water's specific heat (≈4.186 kJ/kg·K), and ΔT is the system's design flow-to-return temperature drop. A radiator needing more heat output, or a system designed around a smaller ΔT, both require proportionally more flow — which is exactly why low-ΔT heat pump systems need noticeably higher flow rates than traditional boiler systems for the same heat output.

Every radiator branch has hydraulic resistance from supply and return pipework, fittings, the emitter and its valves. In many layouts those branch resistances differ, so the hydraulically favoured branches take more flow unless balancing resistance is added. Balancing redistributes flow so each branch approaches its design flow; which branch is most favoured depends on the actual network, not distance alone.

Kv is a valve's flow coefficient: the flow rate (m³/hr) that passes through it at a 1 bar pressure drop. Kv = Q/√ΔP (Q in m³/hr, ΔP in bar) — so for a specific radiator, knowing the flow you need and the pressure actually available at that valve lets you solve directly for the Kv setting required to achieve exactly that flow, deliberately adding just enough extra resistance to bring a well-supplied radiator's flow down to its design value.

This is the differential pressure available across the balancing valve at the design operating condition, after accounting for pressure losses in the rest of that branch and the interacting network. In practice it comes from a hydraulic network calculation or from field measurement during commissioning; this calculator takes it as a known input for each radiator rather than solving the whole pipe network.

The Kv this tool calculates is the target — matching it to an actual valve requires the specific valve manufacturer's own Kv-versus-preset-position data (often a numbered dial or turns-open scale, with a different Kv at each position), since Kv doesn't translate to a universal 'number of turns' across different valve models and sizes. Thermostatic radiator valves with numbered presets, lockshield valves, and pressure-independent balancing valves all publish this data in their technical datasheets.

Heat pumps typically operate most efficiently at a smaller flow-to-return temperature drop (often 5–10K) than traditional gas or oil boiler systems (commonly 20K), and since required flow is inversely proportional to ΔT in the flow rate equation, halving the design ΔT roughly doubles the flow rate needed to deliver the same heat output — which is exactly why heat pump retrofits often require larger pipes, bigger radiators, or both.

Too open (Kv too high for the available pressure) lets that branch take more than its design flow and changes the system pressure distribution, which can reduce flow in less-favoured branches. Too closed (Kv too low) restricts that radiator below its design flow, leaving that room underheated even if the rest of the system is satisfactory.

Approximately, using proportional balancing: set each radiator's valve position proportional to its required flow relative to the others, without needing the exact available pressure figures — this is a common practical field technique, though it converges more slowly and less precisely than calculating the actual required Kv from real available-pressure data, which is what this tool does when you have that data.

In manual balancing practice, yes. Commissioning procedures commonly identify an index or least-favoured circuit and then adjust the other branches iteratively, because each valve adjustment changes the network pressure distribution and can alter other branch flows. This calculator gives an independent target Kv from the pressure value you supply; real commissioning still requires checking the system after adjustments.

A radiator's required flow is driven by how much heat *it* needs to emit to meet the room's demand — which is usually very close to the room's calculated heat loss, but can differ if a room's heat loss is split across more than one radiator, or if a radiator is deliberately oversized relative to the room's actual demand. Enter each radiator's actual intended heat output (from your heat loss calculation, split appropriately) rather than the room's total heat loss if they differ.