Head

For Pumps under suction lift:
H = hd + hs + fd + fs + Vd2/2g

For pumps under suction head:
H = hd - hs + fd + fs + Vd2/2g

Where -

H= Total head in feet = the total head delivered by the pump When the pumping the desired capacity. All heads are measured In feet of the liquid being pumped.

hd = Static discharge head in feet = vertical distance between the pump datum and the surface of the liquid in the discharge bay.

hs = Static suction head or lift in feet = vertical distance from surface of the water in suction bay to the pump datum.

fd = Friction head in discharge in feet = the head required to overcome friction in the pipe, valves, fittings, turns, etc. in the system piping.

Vd2/2g = The velocity head, in feet, at the discharge nozzle of the pump. Velocity head can be defined as the head required to cause the water to attain the velocity "V". (Since the velocity head in most applications will be less than two feet, on high head pumping installation it is a relatively small part of the total head. On lower head applications, it is a significant part of the total head.

Note: In a closed loop system, the pump is not lifting the water. The pump Only needs to over the friction losses of the fluid as it moves throughout the System.

For residential systems, the contractors have been using the following "rule of thumb" for many years to calculate the required pump head:
1. Measure the longest run in feet
2. Add 50% to that
3. Multiply that by 0.04, and
4. That's the pump head

Example:
1. 100 feet of total piping (to radiation and back)
2. 100 feet x 1.5 = 150 feet
3. 150 feet x 0.04 = 6 feet
4. Pump head requirement = 6 feet