Water Hammer Arrestor Calculator
Size water hammer arrestors per PDI WH-201 standard based on fixture units and water pressure.
Inputs
Results
Total fixture units
16
PDI size (0=AA to 6=F)
1
Connection size (in.)0.5
Arrestors needed2
PRV needed?0
Expansion tank needed?0
Peak pressure without (PSI)130
Peak pressure with (PSI)65
Arrestor parts cost$30
Total installed cost$130
Pdi SizeA
How to Use This Calculator
- Count each type of plumbing fixture: bathroom sinks, kitchen sinks, toilets, dishwashers, and washing machines.
- Enter your static water pressure in PSI — if you don't know it, measure at a hose bib with a gauge.
- Review the PDI Size and Arrestors Needed — install one arrestor per solenoid valve (washer, dishwasher).
- Check if a PRV (Pressure Reducing Valve) is flagged — pressures above 80 PSI require one.
- Review Total Installed Cost to budget for the full water hammer solution including PRV and expansion tank.
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