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Calcimator

Backflow Preventer Calculator

Determine the correct backflow prevention device type, size, pressure loss, and estimated installation cost based on hazard level.

Inputs

GPM

Size device to match pipe capacity: 3/4" = 10 GPM; 1" = 20 GPM; 2" = 100 GPM typical

psi

Low hazard: AVB or DCVA; High hazard: RPBA required per IPC 608 and local water authority

inches

Results

Recommended Device

3 (1=AVB, 2=PVB, 3=DCVA, 4=RPBA)

Minimum Device Size

2 inches

Total Pressure Loss11 psi
Estimated Install Cost$1,049.00
How to Use This Calculator
  1. Enter the system flow rate in GPM to size the backflow preventer.
  2. Set the hazard level: 1 = low (irrigation), 2 = medium (chemical boilers), 3 = high (toxic connections).
  3. Enter your supply pipe size to match the device connection diameter.
  4. Review the Recommended Device type — high-hazard applications require a Reduced Pressure Zone (RPZ) assembly.
  5. Use the Estimated Install Cost to budget for device purchase and licensed installation.

How the result changes with Hazard Level

Hazard LevelRecommended DeviceMinimum Device Size
1.23 (1=AVB, 2=PVB, 3=DCVA, 4=RPBA)2 inches
1.73 (1=AVB, 2=PVB, 3=DCVA, 4=RPBA)2 inches
2.34 (1=AVB, 2=PVB, 3=DCVA, 4=RPBA)2 inches
2.84 (1=AVB, 2=PVB, 3=DCVA, 4=RPBA)2 inches

What each input means

Flow Rate
Maximum expected flow rate through the backflow preventer in gallons per minute. IPC 608 and AWWA M14 require backflow prevention at all cross-connections; device must be rated for the design flow.
Downstream Pressure Loss
Additional pressure loss from downstream piping and fixtures.
Hazard Level
Cross-connection hazard classification per IPC 608.1 and AWWA M14. 1 = Low/non-health hazard (irrigation, cooling tower), 2 = Moderate (boiler systems, labs), 3 = High/health hazard (sewage, chemicals).
Supply Pipe Size
Size of the incoming water supply pipe where the device will be installed.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Flow Rate = 50, Downstream Pressure Loss = 5, Hazard Level = 2, Supply Pipe Size = 2 = 4 input(s) provided
  2. Calculate Recommended Device
    Recommended Device
    3 = 3
  3. Calculate Minimum Device Size
    Minimum Device Size
    2 = 2
  4. Calculate Total Pressure Loss
    11 = 11
  5. Calculate Estimated Install Cost
    Estimated Install Cost
    1049 = $1,049

Engine last updated . Checked against 3 independently-derived tests — how we verify calculators.

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