What pipe size do you recommend for my system? | Dry Coolers Inc.

Dry Coolers Inc.

Industrial Process Cooling Systems

Dry Coolers, Inc.
575 South Glaspie Street
Oxford, MI 48371 USA


What pipe size do you recommend for my system?

Typically, the piping should be sized large enough so that frictional pressure drop within the piping system make up less than 10% of the operating pressure of the system. For example, a system operating at 100 psi should have less than 10 psi of frictional pressure losses in the piping system. Pressure losses in a piping system can be readily determined using the "equivalent length" method that is found in most piping handbooks. Since most piping systems are not complex, we have provided a simple table to use as a rule of thumb for sizing the piping. Use this table for systems requiring less than 200’ length of pipe (less than 30’ for gravity drain) and that have a minimum number of valves and bends.

Larger and more complex systems may need special consideration. Consult Dry Coolers for recommendations.

Example: A 150 gpm Vacuum Furnace Cooling System with a plate & frame heat exchanger and a cooling tower. This type of loop has closed-loop process piping and open loop cooling tower piping.

Assume 150 gpm for both loops:

Section of Pipe Minimum Pipe Diameter
Process supply piping to the furnace 3"
Process return piping (from the furnace to the tank) 4"
Cooling tower supply pipe 3"
Cooling tower gravity drain to remote sump tank 5"


Pipe Diameter (in) Max. Supply Piping Flow Rate Max. Return Piping Flow Rate for Furnaces (1) Max. Gravity Return Flow for Remote Towers (2)
1 10 6 2
1.5 35 20 9
2 75 40 22
2.5 120 70 40
3 200 120 63
4 350 250 135
5 550 450 247
6 800 750 400
8 1500 1500 865
10 2500 2500 1570
12 4000 4000 2540

(1) Typically, the back pressure on a furnace must be minimized. The return water piping for a furnace is usually one size larger than the supply pipe. For example, if a furnace requires a 3" supply, then a 4" return is used.

(2) The gravity drain flow returning from a cooling tower is based on a minimum pipe slope of 1/2" / ft with the pipe 3/4 full of water. Based on Manning Formula, n = 0.015. The length of the gravity drain pipe should be kept to a minimum to prevent overflowing the indoor tank and prevent water from backing up in the tower basin.