Hydronic Flow, Pipe Sizing & Pump Head Calculator

Use this preliminary HVAC hydronic calculator page to estimate chilled-water and heating-water flow rate, pipe velocity, pipe pressure drop, equivalent length, and preliminary circulating pump head.

This tool is intended for preliminary engineering reference only. Final hydronic system design, pipe sizing, equipment pressure drop, glycol correction, valve selection, and pump selection should be verified using project requirements, manufacturer data, and applicable design standards.

What This Calculator Will Help Estimate

Chilled-water and heating-water coil flow rate in GPM
Hydronic load conversion between Btu/hr, tons, and kW
Water-side temperature difference, ΔT
Pipe velocity based on flow rate and internal diameter
Pipe pressure drop and head loss by segment
Equivalent length allowance for fittings
Preliminary circulating pump head
Component pressure-drop allowances for coils, valves, strainers, and heat exchangers

Typical Inputs

System type: chilled water or heating water
Coil load in Btu/hr, tons, or kW
Entering and leaving water temperatures
Fluid type and correction factor
Pipe size, material, and internal diameter
Pipe length and fitting equivalent length
Coil pressure drop
Control valve, strainer, heat exchanger, and miscellaneous pressure-drop allowances

Basic Formula References

Hydronic Flow Rate:

GPM = Load / (Fluid Factor × ΔT)

For water near standard HVAC conditions:

GPM = Btu/hr / (500 × ΔT)

Pipe Velocity:

Velocity = 0.4085 × GPM / ID²

where internal diameter is entered in inches.

Pipe Head Loss:

Pipe head loss is calculated using the Darcy-Weisbach relationship, including pipe length, equivalent length, velocity, internal diameter, roughness, and friction factor.

Preliminary Pump Head:

Total Pump Head = Pipe Head Loss + Coil Pressure Drop + Valve Pressure Drop + Strainer Pressure Drop + Equipment Pressure Drop + Allowance

Important Closed-Loop Pump Head Note

For a closed-loop hydronic system, circulating pump head is based primarily on pipe friction and component losses. Building height is not added directly as circulating pump head. Static fill pressure, expansion tank sizing, and air separation should be reviewed separately.

Example

If a cooling coil has a capacity of 120,000 Btu/hr and the chilled-water temperature difference is 10°F:

GPM = 120,000 / (500 × 10)

Required Flow = 24 GPM

Download Excel Calculator

Download the HVACICI hydronic workbook to calculate hydronic flow, pipe sizing, pipe pressure drop, equivalent length, and preliminary pump head.

Download Hydronic Flow & Pump Head Calculator