Short answer
Total Dynamic Head (TDH) is the total resistance your sump pump must overcome to move water from the basin to a safe discharge point. It includes vertical lift, pipe friction, and losses from elbows and fittings. If TDH exceeds what your pump can produce on its pump curve, water recirculates in the pipe while the basement stays wet.
Dive deep
Homeowners often buy pumps by horsepower alone, but horsepower without head calculation is guesswork. TDH combines static head—the vertical distance water must rise—and dynamic head—friction inside the discharge line. Long runs, sharp bends, narrow pipe, and partial clogs all add dynamic head. A pump that performs well in a short, straight discharge may fail when the line climbs a basement wall, crosses a garage, and exits far from the foundation.
Every pump has a pump curve chart showing flow rate at various head heights. As TDH increases, flow drops. At some point, the pump cannot push water out fast enough to keep up with inflow during a Pineapple Express storm. The basin overflows even though the motor runs continuously.
We perform head-loss calculations for each site: measure lift, count fittings, assess pipe diameter and run length, and select a pump whose curve intersects the required flow at your actual TDH. We also specify solid PVC discharge, proper check valves, and battery backup where power loss coincides with peak groundwater. Correct TDH matching is the difference between active water diversion and a pump that spins water in place.
When it applies
- New sump installations or replacements where discharge travels more than a few feet or includes multiple elbows
- Basements that flood despite a running pump—the classic sign of insufficient head capacity
- Long exterior discharge runs to storm drains, dry wells, or daylight outlets uphill from the pit
- Upgrades after interior perimeter drains increase the volume the pump must move per hour
When it does not
- Simple short vertical lifts with minimal friction where a standard cast-iron primary pump is already matched
- Drainage failures caused solely by clogged or frozen discharge lines without pump undersizing
- Groundwater problems that require perimeter drainage design—not just a larger pump on an unchanged pipe
We start with a technical site evaluation—moisture sources, soil behavior, crack pattern, and load direction—before specifying drainage, pumping, or structural scope matched to your property.
What we do next
We calculate TDH, size the pump to the curve, and integrate discharge, check valve, and backup redundancy for PNW storm conditions. Explore sump pump sizing and replacement services built to your site’s head requirements.
