Water Hammer Surge
Calculator
Results
- Surge pressure (Pa)
- 1,800,000
- Surge pressure (bar)
- 18
- Surge head (m of water)
- 183.548918
- Critical valve closing time (s)
- 0.083333
HVAC and plumbing results
| Surge pressure (Pa) | 1,800,000 |
| Surge pressure (bar) | 18 |
| Surge head (m of water) | 183.548918 |
| Critical valve closing time (s) | 0.083333 |
formula-map diagram
- Surge pressure (Pa)
- 1,800,000
- Surge pressure (bar)
- 18
- Surge head (m of water)
- 183.548918
- Critical valve closing time (s)
- 0.083333
HVAC and plumbing relationship
Formula
Δp = ρ × a × Δv= 1800000
Note
This is a simplified model: it applies a standard engineering formula to the numbers you entered. Conversions between BTU/h and kW use the exact factor 1 kW = 3412.142 BTU/h, but every sizing figure is an estimate. Air conditioner sizing uses the common 20 BTU/h per square foot rule of thumb, not a room-by-room load calculation, and it ignores insulation, glazing, orientation, ceiling height, infiltration and local climate. Heating loads use a single volumetric heat-loss factor in W/m³·K rather than a fabric-by-fabric U-value calculation. Air properties are fixed at 1.2 kg/m³ and water at 1000 kg/m³ and 4186 J/kg·K, with no correction for temperature, altitude or glycol. Duct and pipe results use the ideal continuity equation and ignore fittings, bends, roughness and system effect unless you enter those losses yourself. The Hazen-Williams equation is valid only for water in full turbulent flow at ordinary temperatures. Water hammer uses the Joukowsky surge, an upper bound for instant closure. Tank drainage assumes a prismatic tank and steady free discharge. Hot water recovery and condensate figures ignore standing losses and coil bypass. Size real systems with a proper heat-loss survey and have the work checked by a qualified HVAC or plumbing professional.
More in HVAC and plumbing
See all →Frequently asked questions
What causes water hammer in a plumbing system?+
Water hammer occurs when flowing water is suddenly stopped or redirected — typically by a fast-closing valve or solenoid — and the water's momentum converts into a sharp pressure spike that travels through the pipe, often producing a loud banging noise.
Why does valve closing speed matter so much for surge pressure?+
The faster a valve closes, the less time the flowing water has to decelerate gradually, so the pressure spike is larger. A valve that closes in a fraction of a second creates a much sharper surge than one that closes over several seconds.
Does pipe material affect how severe the surge pressure is?+
Yes — more rigid pipe materials (like copper or steel) transmit surge pressure more sharply than more flexible materials (like PEX), because flexible pipe absorbs some of the pressure wave energy through slight expansion.
How does flow velocity before the valve closes affect the surge magnitude?+
Surge pressure increases roughly in proportion to the velocity of the water at the moment of closure, so reducing flow velocity — for example with a larger pipe diameter — is one of the most effective ways to reduce water hammer severity.
How do plumbers typically prevent or reduce water hammer?+
Common solutions include installing air chambers or dedicated water hammer arrestors near quick-closing valves, using slower-closing valves where possible, and ensuring pipes are properly strapped and supported so they can't move when struck by a pressure surge.