Calculate required valve Cv, select valve size, and check valve authority for hydronic balancing applications.
Valve Inputs
Results
Required Cv
—
GPM / √psi
Recommended Cv
—
1.3–1.5× required
Valve Authority
—
ΔPvalve / ΔPsys
Suggested Size
—
nominal pipe size
Standard Balancing Valve Cv Range
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
Select a valve whose Cv range brackets the required Cv with the recommended setpoint at 60–80% open. Valve Cv at full open should be 1.3–1.5× required Cv for adequate rangeability.
Valve Authority Reference
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
Valve Authority β = ΔPvalve / ΔPsystem — When authority is low, a small valve movement causes a large flow change, making the system difficult to balance and control accurately.
Inputs, results, and method — opens in Excel or Sheets.
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.
Formula & Method
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.
Frequently Asked Questions
How is the required Cv for a balancing valve calculated?
Required Cv equals the design flow in GPM divided by the square root of the pressure drop across the valve in psi, with a specific-gravity correction for glycol: Cv = GPM divided by the square root of (Delta-P divided by SG). For water the specific gravity is 1.0. This tool then recommends a valve with full-open Cv about 1.4 times the required Cv so the valve operates in its controllable mid-range.
What is valve authority and why does it matter?
Valve authority, beta, equals the pressure drop across the valve divided by the total system pressure drop of the controlled circuit. It measures how much of the circuit resistance the valve controls. Authority at or above 0.5 is excellent, 0.25 to 0.5 is acceptable, and below 0.25 is poor because small valve movements cause large flow swings, making the loop hard to balance.
Why size the valve Cv at 1.3 to 1.5 times the required value?
A balancing or control valve should run partly open at design flow, not wide open, so it retains rangeability and the ability to trim flow. Selecting a full-open Cv about 1.3 to 1.5 times the required Cv puts the valve near 60 to 80 percent open at design, leaving room to balance the circuit. This tool uses 1.4 times as the midpoint.
How does glycol change the required Cv?
Glycol raises the fluid specific gravity above 1.0, which slightly increases the required Cv for the same flow and pressure drop because Cv is divided by the square root of (Delta-P divided by SG). Select your fluid from the dropdown and the tool applies the specific gravity automatically. The larger effect of glycol is usually its higher viscosity, which raises system pressure drop separately.
This calculator handles one step. AIM Works runs the complete MEP design workflow — thermal load calculations, duct & pipe networks, equipment selection, code compliance, and an AI design assistant — in one tool.
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.