Calculator inputs
Example data table
| Scenario | Mode | Flow | ΔP | Kv/Cv | Fluid | Typical outcome |
|---|---|---|---|---|---|---|
| Fan coil branch | Required coefficient | 0.60 L/s | 25 kPa | Find Kv | Water 20°C | Kv ≈ 4.27, then choose nearest setting. |
| AHU coil balancing | ΔP from flow | 9.0 m³/h | Find ΔP | Kv 10.0 | 30% glycol | Higher SG increases required ΔP. |
| Parallel risers (2 valves) | Flow from ΔP | Find flow | 15 kPa | Cv 8.0 | Water 15°C | Total flow equals twice per-valve flow. |
Formula used
The calculator uses standard valve coefficient relationships with a specific gravity correction. For SI sizing:
- Q = Kv × √(ΔP / SG) where Q is in m³/h and ΔP is in bar.
- ΔP = SG × (Q / Kv)² gives the valve pressure drop in bar.
- Kv = Q × √(SG / ΔP) solves the required coefficient for a design point.
For US coefficients, the tool converts Cv to Kv using Kv ≈ 0.865 × Cv for quick comparisons.
How to use this calculator
- Select the calculation mode based on what is unknown.
- Choose coefficient type and enter either Kv or Cv.
- Enter flow and/or differential pressure with your units.
- Set temperature and glycol percentage for fluid correction.
- Add valve quantity for parallel branches if applicable.
- Submit to view results above the form instantly.
- Use CSV or PDF buttons to export your calculation record.
Professional article: balancing valves in hydronic construction
1) Why balancing matters on site
Balancing valves help deliver the designed water flow to each branch, coil, and terminal unit. Without controlled flow, some circuits “steal” flow while others starve, causing uneven temperatures, noisy operation, and wasted pumping energy. A consistent balancing method reduces rework and supports smoother handover.
2) What a balancing valve controls
A manual balancing valve creates a measurable pressure drop across an adjustable restriction. With test ports, technicians measure differential pressure (ΔP) and relate it to flow using a valve coefficient at the operating point.
3) Understanding Kv and Cv
Kv (metric) and Cv (US) describe how much flow passes for a given pressure drop. Kv is typically m³/h at 1 bar for water; Cv is gpm at 1 psi. Converting keeps sizing checks consistent across mixed submittals.
4) Fluid correction for glycol mixes
Glycol raises specific gravity (SG), which shifts the flow–pressure relationship. Using SG correction avoids underestimating required ΔP or selecting an overly aggressive valve setting, especially during cold-weather operation.
5) Selecting a realistic design ΔP
Designers allocate a target ΔP across balancing devices to maintain authority and measurement resolution. Too low and flow estimates become sensitive to small reading errors; too high and pumping energy rises. A safety factor provides a practical margin for checks.
Documenting each calculation is just as important as the final valve setting. A clear record of units, fluid mix, and the assumed ΔP helps the team reconcile field readings with design intent during troubleshooting and seasonal changeover.
6) Example data: compute a required Kv
Example: a fan-coil branch needs 0.60 L/s and you can allocate 25 kPa across the valve. Convert flow: 0.60 L/s = 2.16 m³/h. Convert ΔP: 25 kPa = 0.25 bar. With water (SG ≈ 1.00), Kv = Q × √(SG/ΔP) = 2.16 × √(1/0.25) = 4.32. Select the nearest setting and confirm on the valve chart.
7) Example data: estimate ΔP for a known setting
Example: an AHU coil requires 9.0 m³/h through a valve set to Kv = 10.0. With 30% glycol and SG ≈ 1.04, ΔP = SG × (Q/Kv)² = 1.04 × (9/10)² ≈ 0.84 bar (≈ 84 kPa).
8) Practical commissioning tips
Ensure measurement points are across the balancing valve only, and pumps are at the intended speed. Record valve position, ΔP, and computed flow. After adjustments, re-check interacting branches. Final acceptance should follow the manufacturer’s published curves.
FAQs
1) What is the difference between a balancing valve and a control valve?
A balancing valve is used to set and verify design flow. A control valve modulates flow automatically for temperature or pressure control. Many systems use both: balance for design, control for operation.
2) Should I use Kv or Cv on a construction project?
Use the coefficient shown on your valve chart and submittals. If documentation mixes systems, convert to a single basis so sizing checks are consistent, then verify final settings with the manufacturer curve.
3) Why does glycol change my balancing results?
Glycol increases specific gravity, which increases the ΔP required for the same flow at the same valve setting. Ignoring this can cause underflow during cold conditions or incorrect commissioning records.
4) What ΔP should I aim for across a balancing valve?
It depends on design intent and valve type. Use project specifications or design notes. A higher ΔP improves measurement resolution but can increase pump energy. Use a margin if conditions vary.
5) Can I split one design flow across multiple parallel valves?
Yes, if branches and valves are identical and arranged in parallel, flow can be assumed to split evenly. This calculator divides total flow by the valve quantity for per-valve ΔP and Kv checks.
6) Why do my calculated values differ from the valve chart?
Manufacturer charts include valve geometry, Reynolds effects, and the exact relationship between setting and coefficient. Use this tool for engineering checks and documentation, then confirm final numbers on the chart.
7) What should I export for commissioning records?
Export inputs and outputs for each measured point: valve ID/location, valve setting, fluid mix, temperature, measured ΔP, and computed flow. Attach the manufacturer curve used for the final verification.
Accurate balancing improves comfort, savings, reliability, and commissioning confidence.