Pipe Head Loss

Critical-path head for a hydronic circuit: pipe segments by equivalent length plus equipment losses.

System Settings
Circuit Components
Summary
Pipe Friction
—
ft head
Equipment Head
—
ft head
Total Head
—
ft head
Pressure Drop
—
psi
Circuit Breakdown
TypeComponentGPMSizeEquiv. L (ft) Vel. (ft/s)Head (ft)
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About This Calculator

This pipe head loss calculator builds the total head a hydronic pump must overcome along a circuit. Add pipe segments (flow, size, and equivalent length) and equipment items (coils, chillers, control valves, strainers) with their water-side head loss; the tool sums them into total head in feet and pressure drop in psi for pump selection.

Each pipe segment is evaluated with the Darcy–Weisbach equation using the Colebrook–White friction factor, with fluid density and viscosity interpolated by temperature from published property data for water or 30, 40, or 50% (by volume) ethylene or propylene glycol. Equipment items are entered as fixed losses from manufacturer data. Build the loss along the longest (critical) path to size the pump.

Formula & Method
VelocityV (ft/s) = Q (GPM) × 0.002228 ÷ A   A = π · (d ÷ 24)²
Head losshL = f · (L ÷ D) · V² ÷ (2 · g)
Total headHtotal = Σ hL,pipe + Σ hequip
PressureΔP (psi) = H (ft) · ρ ÷ 144

Pipe friction uses Darcy–Weisbach with the Colebrook–White friction factor (f = 64 ÷ Re below Re ≈ 2,300), the standard basis in ASHRAE Fundamentals and Cameron Hydraulic Data. The constant 0.002228 converts GPM to ft³/s; g = 32.174 ft/s². Reynolds number is V · D · (ρ ÷ gc) ÷ μ. Pipe head is in feet of the flowing fluid. Head converts to pressure with ΔP = H · ρ ÷ 144, which for cold water is about feet ÷ 2.31. Inside diameters and roughness match the Hydronic Pipe Sizer; water properties follow IAPWS (NIST), glycol viscosity is Dow inhibited-glycol data as tabulated in ASHRAE Fundamentals, and glycol density is from MEGlobal (ethylene) and Melinder (propylene) correlations. Segments above 8 ft/s (a common noise and erosion rule of thumb) are flagged. Equivalent length is the straight run plus the equivalent length of its fittings and valves. Equipment head losses are taken from manufacturer cut sheets at design flow.

Frequently Asked Questions
How do I find the head loss for pump sizing?
Add the friction loss of every pipe segment along the longest (critical) flow path, then add the water-side head loss of each piece of equipment on that path, such as coils, chillers, control valves, and strainers. The sum is the total head the pump must overcome at design flow. This tool builds that total segment by segment and reports it in feet of head and psi.
Why does the tool ask for the critical path and not every pipe?
In a closed hydronic loop the pump only needs to overcome the head of the single most-resistive circuit, called the critical or index path, not the sum of all parallel branches. Balancing valves throttle the easier branches to match. So you build the head loss along that worst-case path, which sets the pump head requirement.
How is feet of head converted to psi?
Pressure in psi equals head in feet times fluid density in pounds per cubic foot divided by 144. For water near 60 degrees Fahrenheit this is roughly head in feet divided by 2.31. The tool uses the actual interpolated density at your fluid temperature, so glycol and hot water convert slightly differently from cold water.
Where do I get the equipment head loss values?
Use the manufacturer's published water-side pressure drop for each coil, chiller, heat exchanger, and control valve at your design flow. These are listed in equipment cut sheets and selection software. Enter each as feet of head; the tool treats them as fixed losses and adds them to the pipe friction along the path.
Related Tools
Pump Selector Pump Head Estimator Hydronic Pipe Sizer Pipe Velocity & Friction Balancing Valve Cv Pipe Insulation Heat Loss Control Valve Cv
AIM Works · launches Oct 15, 2026

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Results are design estimates for preliminary sizing. Verify final designs against applicable codes and standards — engineering judgment and a licensed professional engineer’s review are required.