Darcy-Weisbach velocity and friction loss for one pipe size and flow, checked against typical limits.
| Application | Max Velocity | Notes |
|---|---|---|
| Pump suction | 3 ft/s | Prevent cavitation and noise |
| Branch / zone supply | 4 ft/s | Low-noise terminal units |
| Main distribution headers | 8 ft/s | Common upper limit for noise and erosion |
| Condenser water | 10 ft/s | Larger pipe, higher tolerance |
| Friction loss target | 1–4 ft/100ft | Design target for sizing |
| Domestic cold water | 8 ft/s | Copper tube, cold service |
| Friction loss max | 4 ft/100ft | Above this → velocity noise risk |
| Rules of thumb from common design practice, not code limits. Check the project specification and the equipment maker’s limits. | ||
Doing this for a whole building? See this step inside a connected AIM Works project — loads, ventilation, equipment, and Design Review in one place.
Book a Demo →This pipe velocity and friction checker computes water velocity, friction loss, and Reynolds number for any nominal Sch 40 pipe size and flow rate. Enter the flow in GPM, pick a pipe size, fluid, and temperature, and choose an application; the tool returns velocity in ft/s and friction loss in feet per 100 feet, with pass/fail badges against typical design velocity limits.
Velocity that is too high causes noise and erosion-corrosion; too low risks sediment settling. The application selector applies the right velocity ceiling for branch lines, mains, pump suction, condenser water, and domestic cold, so you can confirm a size before committing it.
| Velocity | V (ft/s) = Q (GPM) ÷ 449 ÷ A A = π · d² ÷ 4 (ft) |
| Reynolds | Re = V · D ÷ ν |
| Friction f | Colebrook–White (turbulent); f = 64 ÷ Re (laminar) |
| Friction loss | hL = f · (100 ÷ D) · V² ÷ (2 · g) (ft/100 ft) |
Friction uses the Darcy–Weisbach equation with the Colebrook–White friction factor, solved iteratively, per ASHRAE Fundamentals hydronics. The constant 449 converts GPM to ft³/s (1 ft³/s ≈ 448.8 GPM); ν is the fluid kinematic viscosity at your temperature (water at 60°F ≈ 1.21 × 10⁻⁵ ft²/s); steel roughness ε ≈ 0.00015 ft; g = 32.174 ft/s². Below Re ≈ 2,300 the flow is laminar and f = 64 ÷ Re. Friction is in feet of the flowing fluid per 100 ft. 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 — the same data as the Hydronic Pipe Sizer. The velocity limits are common rules of thumb, not code requirements.
AIM Works brings peak loads, ASHRAE 62.1 ventilation, equipment and plant sizing, compliance checks, Design Review, and engineering deliverables into one connected mechanical design workspace.
Duct and pipe distribution sizing is planned for V2 — at launch, keep using this calculator for that step.
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.