Water Conditioning (C-55) · Lesson 1 of 5

Sizing the Residential Softener Connection (CPC 611.4)

"Sizing the Residential Softener Connection (CPC 611.4)" is lesson 1 of 5 in the Water Conditioning (C-55) Learning Hub. It opens with "Where the Code Sizes a Softener" and works through 6 short steps, then a worked example you can check yourself against.

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Steps in this lesson

  1. Where the Code Sizes a Softener
  2. Count Bathroom Groups, Not Fixtures
  3. Read the Table: 3/4 Inch Up to 2, 1 Inch Up to 4
  4. Over Four Groups Is an Engineering Job
  5. Do Not Forget the Pressure Loss
  6. Match the Listing Standard (Table 611.1)

The worked example in the course applies this lesson to a realistic job in 5 steps, from "Count the bathroom groups" through "What changes if the owner adds a third full bath?".

What you'll be able to do

  • Explain the main idea of "Sizing the Residential Softener Connection (CPC 611.4)" in plain language you can use on the exam.
  • Apply this step with confidence: "Read the Table: 3/4 Inch Up to 2, 1 Inch Up to 4".
  • Apply this step with confidence: "Over Four Groups Is an Engineering Job".
  • Apply this step with confidence: "Do Not Forget the Pressure Loss".
  • Apply this step with confidence: "Match the Listing Standard (Table 611.1)".
  • Test yourself on the worked example and the quick-check quiz inside the classroom.
Sizing the Residential Softener ConnectionSTEP 1: COUNT BATHROOM GROUPSMaster bath: 1 WC, 2 lav, tub, shower= 1Hall bath: 1 WC, 1 lav, bath/shower= 1Half bath: 1 WC + 1 lavnote 2: no increaseKitchen sink + dishwashernote 1: no increaseLaundry sink + clothes washernote 1: no increaseBathroom groups served= 21 group = at most 1 WC, 2 lav, 1 tub or combo, 1 showerTABLE 611.4 (RESIDENTIAL)Bathroom groupsConnectionup to 23/4 inchup to 41 inchover 4engineered (note 3)STEP 2: PRESSURE-LOSS RULE, CPC 610.2No pressure-drop data on the device:inlet/outlet or connecting pipe ≥distribution pipe size (3/4 in here)SOFTPoint-of-entry unit, listed to NSF/ANSI 44 (CPC Table 611.1)Water in, softener, conditioned water out to the house piping2 bathroom groups + half bath + kitchen/laundry = 3/4 inch connectionA third full bath makes 3 groups: 1 inch. Over 4 groups: engineer it.Source: 2025 California Plumbing Code Tables 611.4 and 611.1, Section 610.2, Chapter 2 definitionsCC
The diagram for this lesson, exactly as it appears in the Learning Hub.

The first steps of this lesson

Step 1: Where the Code Sizes a Softener

A residential water softener is sized by the plumbing code, not by guesswork. 2025 CPC Section 611.4 says residential-use water softeners "shall be sized in accordance with Table 611.4." The table sizes the softener CONNECTION (the inlet/outlet pipe size), and a point-of-entry unit is defined in CPC Chapter 2 as a device serving the water distribution system of a building.

Step 2: Count Bathroom Groups, Not Fixtures

Table 611.4 is entered by the number of bathroom groups served. CPC Chapter 2 defines a bathroom group as any combination of fixtures, not to exceed one water closet, two lavatories, either one bathtub or one combination bath/shower, and one shower, and it may include a bidet and an emergency floor drain. A master bath with a water closet, two lavatories, a tub and a separate shower is therefore ONE group, not five fixtures.

The remaining 4 steps, the worked example and the quiz are in the course. This is a preview. The full lesson, with the step-by-step explanations, a worked example and a quick-check quiz, is inside the classroom.

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