Calculation Results
About This Calculator
Size plumbing water hammer arrestors according to PDI WH-201 and ASSE 1010 standards based on plumbing fixture units (PDI Class A through F).
Frequently Asked Questions
What causes water hammer in residential plumbing?
Water hammer occurs when fast-closing electric solenoid valves (in washing machines, dishwashers, or ice makers) snap shut in milliseconds. Moving water possesses momentum; slamming the valve creates a shockwave up to 400+ PSI that rattles pipes and damages joints.
Why are sealed mechanical water hammer arrestors required instead of air chambers?
Old-fashioned copper pipe capped 'air chambers' quickly fill with water as air dissolves into the water supply, rendering them useless. Modern ASSE 1010 arrestors feature a permanently pre-charged nitrogen gas piston sealed with double O-rings that never waterlogs.
Where should a water hammer arrestor be installed?
PDI WH-201 guidelines mandate installing arrestors within 6 feet of the fast-closing valve. Installing them directly on washing machine hose bibbs is the most effective location.
What PDI size is needed for a single washing machine?
A standard residential clothes washer has a rating of 4 Fixture Units, which is fully protected by a PDI Size A arrestor (rated for up to 32 Fixture Units).