Pump Head Calculator (TDH) — Friction + Static
Calculate the total dynamic head for a hydronic circulator by summing pipe friction, fitting friction, static elevation, and terminal-device pressure drop.
- Enter flow, pipe, and length Enter Design flow rate in GPM, choose the Pipe material and Pipe size (NPS), and enter the Total pipe length in feet (supply plus return).
- Enter the terminal device drop Enter Terminal device drop in psi — the combined pressure drop of the boiler, coil, and balance valve. The tool converts this to feet of head using 0.4332 psi per foot of water.
- Set fitting counts and elevation Open the advanced inputs to set 90° elbows, Tees (straight-thru), Ball valves (open), and Elevation gain. These default to typical residential values (6 elbows, 2 tees, 2 valves, 0 ft).
- Calculate and plot Press Calculate to get total dynamic head in feet and psi, with a velocity warning if flow exceeds 4 ft/s. Plot the (GPM, head) design point on a manufacturer pump curve to select a circulator.
How do I calculate pump head for a hydronic circulator?
Total dynamic head is the sum of pipe friction, fitting friction, static elevation change, and terminal-device pressure drop. This calculator computes pipe and fitting losses with the Hazen-Williams head-loss method and the ASHRAE equivalent-length approach for fittings, adds elevation directly, and converts the terminal psi drop to feet at 0.4332 psi per foot. The result is the design point you plot against a pump curve.
How are fittings accounted for in pump head?
Each 90° elbow, straight-through tee, and ball valve is converted to an equivalent length of straight pipe and added to the friction calculation. The tool ships with typical residential defaults (6 elbows, 2 tees, 2 valves) that you can override in the advanced inputs. This follows the standard equivalent-length method used in ASHRAE hydronic design.
What pump velocity is too high in a hydronic loop?
Above 4 ft/s the tool warns of high velocity, and at or above 8 ft/s it flags cavitation risk because pump-suction NPSH-available margins become inadequate. The fix is to reduce flow, increase pipe size, or split the loop rather than fighting the noise and erosion with a bigger pump.