Which of the following is not a significant factor in calculating friction loss?

• A. Pipe Length
• B. GPM
• C. Water Temperature
• D. Pipe Diameter

Answer: (C)

Friction loss in hoses and piping comes from the resistance the moving water encounters along the length of the line. The factors that drive this loss are the length of the hose, the size of the hose (diameter), and how much water you’re moving (the flow rate, shown as GPM). More length means more contact and more friction. A smaller diameter forces water to move faster for the same flow, increasing friction as velocity and turbulence rise. A higher flow rate likewise increases friction because the water is moving more vigorously through the same or similar diameter, amplifying resistance.

Water temperature, while it does affect water viscosity slightly, is not treated as a significant factor in standard friction-loss calculations for firefighting. The typical formulas assume standard water properties, so changes in temperature within normal ranges don’t meaningfully alter the friction loss. That’s why water temperature isn’t considered a major factor, while length, diameter, and flow rate are.