IPC Pipe Sizing Guide

The International Plumbing Code (IPC) provides a prescriptive pipe sizing methodology in Appendix E. Plumbing Booster implements this methodology end-to-end: from fixture unit summation through flow-rate conversion to final pipe diameter selection. This guide walks through each step so you can understand exactly what the software calculates and why.

IPC pipe sizing follows a five-step process: 1. **Sum WSFU** — For each pipe segment, sum the Water Supply Fixture Units (WSFU) of all fixtures served. Cold and hot water loads are tracked separately. 2. **Convert WSFU to GPM** — Use IPC Table E103.3(3) to convert total WSFU to a flow rate in GPM. Separate columns exist for flush-tank systems and flushometer-valve systems. 3. **Select pipe size** — Use IPC Table E104.1 to find the smallest pipe that can carry the calculated flow at the available pressure. 4. **Verify velocity** — Check that the resulting velocity falls within the IPC-recommended range of 4-8 ft/s (1.2-2.4 m/s). 5. **Map to material** — Convert the IPC nominal inch size to the equivalent PPR, PEX, Copper, or CPVC outer diameter.

Key IPC tables used: - **Table E102.3(2)** — Fixture unit values for water supply - **Table E103.3(3)** — Supply system demand (WSFU to GPM conversion) - **Table E104.1** — Minimum size of water meters, mains, and distribution piping - **Table 604.3** — Required pressure at fixture outlets

Consider a branch serving two bathrooms on a single floor: - 2 x Water closet (flush tank): 2 x 2.5 = 5 WSFU cold, 0 WSFU hot - 2 x Lavatory: 2 x 0.5 = 1 WSFU cold, 1 WSFU hot - 1 x Bathtub: 1 x 4 = 4 WSFU cold, 4 WSFU hot - **Total cold WSFU = 10, Total hot WSFU = 5** From Table E103.3(3) for flush-tank systems: 10 WSFU = 14 GPM cold, 5 WSFU = 10 GPM hot. From Table E104.1, 10 WSFU requires a minimum 1/2" distribution pipe. However, checking velocity at 14 GPM through 1/2" pipe gives ~11 ft/s - above the 8 ft/s limit. The software upsizes to 3/4" to bring velocity within range. Final result: **3/4" IPC nominal -> 25mm PPR (PN10 SDR 11)** with velocity ~5.2 ft/s.

In the Domestic Water module: 1. Enter fixtures in the Wet Areas Configuration page - WSFU is auto-calculated from the selected code table. 2. Choose "IPC Table-Based" as the pipe sizing method in System Structure. 3. The System Summary page shows the selected pipe size, flow rate, velocity, and compliance status for every branch and riser. 4. The Riser Diagram page visualizes the pipe sizes on an interactive SVG diagram.