FixtureUnitFixture units in, pipe size out — the table the code actually uses.

FixtureUnit

Fixture units in, pipe size out — the table the code actually uses.

SectionsLatest
Supply SizingWSFU to pipe diameter, and what pressure and length do to it.57
Drain & Waste SizingDFU to drain size, and the slope every horizontal run needs.77
VentingWhy traps siphon, and what the vent is doing about it.45
PEX, Copper & CPVCCost, lifespan and where each one is a bad idea.76
Repipe CostWhole-house repipe by fixture count and bathroom count.1702
  1. Water Supply Fixture Units — Counting Demand That Never All Happens at OnceSupply Sizing · 3 min read

    Add up every fixture's flow rate and you get a number no house has ever drawn.

  2. Drainage Fixture Units — Sizing Drains and Why Bigger Is Not BetterDrain & Waste Sizing · 3 min read

    A drain has to be big enough to carry the flow and small enough to keep it moving.

  3. Why Drains Need Vents — Trap Seals and Air PressureVenting · 3 min read

    The pipes are half plumbing and half air, and the air half is the one nobody sees.

  4. PEX, Copper or CPVC — Choosing Supply PipePEX, Copper & CPVC · 3 min read

    Three materials, three sets of trade-offs, and the installer's familiarity matters more than most of them.

  5. Slope and Fittings — Why Drains Block Where They DoDrain & Waste Sizing · 3 min read

    Drainage runs on gravity and geometry, and both are easy to get wrong in ways that only show up years later.

  6. House Water Pressure — The Right Range and What Too High CostsSupply Sizing · 3 min read

    A gauge on a hose bib costs very little and it answers a question most households have never asked.

  7. Wet Venting — Using a Drain as a Vent, Where the Code Allows ItVenting · 3 min read

    It sounds like a shortcut and it is a defined arrangement with rules, which is why copying one from a photograph goes wrong.

  8. Manifold or Trunk and Branch — Two Ways to Lay Out Supply PipeSupply Sizing · 3 min read

    Every fitting buried in a wall is a joint that can leak, and one of these layouts has almost none.

  9. Traps — The Water Seal, and the Four Ways It DisappearsDrain & Waste Sizing · 3 min read

    There is a small amount of water standing under every drain in the house, and it is the only thing between the room and the sewer.

  10. The Line to the Street — Roots, Bellies and Camera InspectionsDrain & Waste Sizing · 3 min read

    Everything in the house drains through one pipe, and it is the one nobody can see.

  11. Drain, Waste and Vent Materials — PVC, ABS and Cast IronPEX, Copper & CPVC · 3 min read

    A plastic stack in a wall behind a bedroom is audible in a way a cast iron one is not.

  12. Repipe or Repair — When Patching Stops Making SenseRepipe Cost · 3 min read

    The second pinhole in a year is not a coincidence, and the third one will not be either.

  13. Shutoff Valves — The Ones That Seize and the Ones That MatterSupply Sizing · 3 min read

    The moment a valve is needed is not the moment to discover it will not turn.

Drain size by fixture units

72 calculations · Drain & Waste Sizing · browse all

PEX, copper and CPVC

72 calculations · PEX, Copper & CPVC · browse all

Whole-house repipe cost by city

1,494 calculations · Repipe Cost · browse all