100 Level

102 - Chapter 3

Estimating Friction Head

The friction from restrictive plumbing can force the pump to work as hard as if it were lifting water three or four times higher than the waterfall, effectively tripling or quadrupling the head, which means a lot less water flow than you’re paying for. To keep this ‘Friction Head’ to a minimum, always increase the plumbing 1-2 sizes larger than the outlet of the pump. If the outlet is ¾”, use 1” or larger plumbing. If it’s 1½”, go up to 2” tubing. With upsized plumbing, you can use the following Total Dynamic Head Rule of Thumb:

Estimating Total Dynamic Head:

After upsizing plumbing 1 -2 sizes larger than pump discharge:

For every 10' of Tubing, add 1 foot of Head

For every Check Valve, add 1' of Head

For every fitting, add ½' of Head


So, if your waterfall is 4 feet tall, with 10 feet of tubing, two elbows and a check valve, your system would have a THD of 4 + 1 + 1 + 1 = 7’.   Now you can check the charts to see which pump gives the flow you need at 7’ Head. If there’s a choice, look for the pump that uses the least Wattage; that’ll cost you the least to run.