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Heating pipe diameter selection
Fluid type
Fluid temp. °C
Pipe type
Selection based on power
Power kW
Temp. difference °C
Selection based on flow
Flow m3/h
Flow dm3/s
Heating pipe diameter calculator — central heating pressure drop sizing
Professional calculator for sizing pipe diameters in central heating systems. Linear pressure losses are computed using the Darcy-Weisbach equation, with the friction factor solved from the Colebrook-White equation, for eight pipe series (steel, copper, PEX, PERT/AL/PERT, PE PN10/PN16, PP PN16/PN20). The calculator supports water and glycol mixtures (propylene, ethylene) across the full temperature range used in hydronic heating — from low-temperature underfloor systems up to classic 80/60 °C radiator parameters. A tool for HVAC designers, installers and service engineers.
How to use the calculator in 3 steps
Choose the heat carrier (water or glycol mixture) and set the supply temperature. The calculator picks the corresponding density, viscosity and specific heat for the selected fluid and temperature.
Enter the calculation parameters — pick a mode: sizing by heating power (kW) and temperature difference Δt, or sizing directly from flow (m³/h or dm³/s).
Read the results: for every pipe series you get a full list of diameters together with flow velocity v [m/s] and unit pressure drop Δp [Pa/m]. Pick the diameter that meets your design criteria.
Sizing by power vs sizing by flow
"By power" mode — when you know the heat load of the consumer (e.g. radiator output, sum of manifold loops, boiler capacity). The calculator derives the mass flow from the heat balance equation: Q = ṁ · cₚ · Δt, where Q is the heat output [W], ṁ — the carrier mass flow rate [kg/s], cₚ — specific heat (≈ 4190 J/(kg·K) for water, lower for glycol mixtures — the calculator picks the right value for the selected fluid and temperature), Δt — the supply-return temperature difference [K]. Typical temperature differentials for radiator heating: 80/60 °C (Δt = 20 K), 70/55 °C, 55/45 °C, while underfloor heating uses 45/35 °C or 35/28 °C.
"By flow" mode — when you are designing a section downstream of a manifold, you already know the flow from a hydraulic balance, or you are sizing a circulator pump from the required capacity. You enter the flow directly in m³/h or dm³/s — the calculator converts between units automatically.
Both modes are equivalent — the choice depends on which data you happen to have at the current design stage.
Recommended design values for pumped central heating systems
The values below follow standard Polish design practice (Recknagel, Mizielińska, Koczyk) and let you design an installation that is reasonably priced, energy-efficient to run, and acoustically comfortable.
- Velocity in risers: 0.5–1.0 m/s — values in this range provide proper energy transport without excessive pressure losses.
- Velocity in basement distribution headers: 0.3–0.7 m/s — larger diameters and longer runs prefer lower velocities.
- Velocity in radiator branches: below 0.5 m/s — critical for acoustic comfort in residential rooms.
- Unit pressure drop (R, Δp/L): typically 100–200 Pa/m, with an acceptable maximum around 250 Pa/m. 160 Pa/m is a common default design point.
- Maximum velocity for acoustic comfort: 1.0 m/s in residential rooms (bedrooms, living rooms, offices) and up to 1.2 m/s in technical rooms. Values above 1.5 m/s carry a high risk of hydrodynamic noise, pipe wall erosion and premature wear of fittings.
- Glycol mixtures — the higher viscosity of the carrier causes higher pressure losses at the same flow. The increase can be substantial, especially at lower operating temperatures and higher glycol concentrations (for a 40% solution at 0–10 °C it can reach as much as 50–100% compared to pure water). The calculator accounts for this automatically based on the selected fluid and temperature.
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