Size a hot water pipe based on demand flow rate using a lower recommended velocity to reduce noise and heat loss.
How to Use the Hot Water Pipe Calculator
Enter the total "Hot Water Demand (L/min)" for the fixtures being served.
Enter the "Design Velocity (m/s)", or keep the default of 1.0 m/s recommended for hot water.
Click "Calculate" to see the calculated diameter and the recommended standard pipe size.
Frequently Asked Questions
Lower velocities (around 0.9-1.2 m/s vs 1.0-2.0 m/s for cold water) reduce noise, water hammer risk, and heat loss along the pipe run, which matters more for hot water distribution.
It uses the same continuity equation as cold water sizing — Diameter = √(4 × Flow ÷ (π × Velocity)) — but defaults to a lower velocity suited to hot water systems, then rounds up to the nearest standard pipe size.
CPVC and copper are common choices for hot water since they handle higher temperatures reliably; standard PVC is not recommended for hot water as it can soften/deform.
Yes, it's completely free and requires no sign-up.