| Pipe Size | Min Cv | Max Cv | Typical Max Flow (GPM @ 2 psi) | Match |
|---|---|---|---|---|
| ½" | 0.3 | 4.0 | 5.7 | |
| ¾" | 0.5 | 6.3 | 8.9 | |
| 1" | 1.0 | 10.0 | 14.1 | |
| 1¼" | 2.0 | 16.0 | 22.6 | |
| 1½" | 4.0 | 25.0 | 35.4 | |
| 2" | 6.3 | 40.0 | 56.6 | |
| 2½" | 10.0 | 63.0 | 89.1 | |
| 3" | 16.0 | 100.0 | 141.4 | |
| 4" | 40.0 | 160.0 | 226.3 |
| Authority (β) | Control Quality | Recommendation |
|---|---|---|
| β ≥ 0.50 | Excellent | Ideal for critical control loops |
| 0.25 ≤ β < 0.50 | Acceptable | Satisfactory for most applications |
| β < 0.25 | Poor | Valve has insufficient authority — increase ΔP or reduce system ΔP |
This balancing valve Cv calculator finds the required flow coefficient for a hydronic balancing valve from the design flow and the pressure drop you allocate across the valve. Enter the flow in GPM, the valve ΔP in psi, and the fluid; the tool returns the required Cv, a recommended full-open Cv (about 1.4× required), a suggested nominal valve size, and the valve authority for the circuit.
Cv (the valve flow coefficient) is the GPM of water a valve passes at 1 psi drop. A glycol fluid raises specific gravity, which the tool applies automatically. The authority check (β = ΔPvalve ÷ ΔPsystem) confirms the valve controls enough of the circuit resistance to balance reliably.
| Required Cv | Cv = GPM ÷ √(ΔP ÷ SG) |
| Recommended Cv | Cvsel = 1.4 × Cv (1.3–1.5× required) |
| Valve authority | β = ΔPvalve ÷ ΔPsystem |
Cv sizing follows the standard valve flow-coefficient relation used in manufacturer Cv data and ISA-75 valve-sizing practice: Cv is the GPM of 60°F water passed at a 1 psi drop, so Cv = GPM ÷ √(ΔP) for water (SG = 1.0). The specific-gravity term SG generalizes it to glycol; this tool reads SG from the fluid dropdown (water 1.00, up to 50% ethylene glycol 1.085). Authority β thresholds (≥0.50 excellent, 0.25–0.50 acceptable, <0.25 poor) follow standard hydronic balancing practice.