1. What are Fixture Units in Plumbing?

Definition: Fixture Units (FU) are dimensionless numbers that represent the load-producing effect of plumbing fixtures on the drainage system.

Purpose: Used by plumbers and engineers to properly size pipes and drainage systems based on the expected usage of water fixtures.

2. How to Calculate Fixture Units?

The calculation uses the formula:

Where:

• \( FU_{total} \) — Total fixture units for the system
• \( FU_{item} \) — Fixture unit value for each plumbing fixture

Explanation: Each type of plumbing fixture is assigned a standard fixture unit value. The total is the sum of all fixtures' units in the system.

3. Importance of Fixture Unit Calculation

Details: Proper calculation ensures adequate pipe sizing, prevents drainage problems, and meets building code requirements.

4. Using the Calculator

Tips:

1. Select fixture types from the dropdown
2. Enter quantities for each fixture
3. For custom fixtures, select "Custom" and enter the FU value
4. Click "Add More Fixtures" if needed
5. Press "Calculate" to get the total

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between water supply and drainage fixture units?
A: They're often similar but can differ. This calculator uses drainage fixture units (DFU) which are typically higher.

Q2: How do fixture units relate to pipe sizing?
A: Plumbing codes provide tables showing maximum fixture units allowed for different pipe diameters.

Q3: Why do toilets have higher fixture units?
A: Toilets produce sudden large discharges that impact drainage systems more than smaller fixtures.

Q4: Can fixture units be added for different branches?
A: Yes, calculate separately for each branch then sum them appropriately for the main drain.

Q5: Where can I find standard fixture unit values?
A: Most plumbing codes (IPC, UPC) include tables of standard fixture unit values.