Fixture Unit Troubleshooting

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Hose Bibbs Are the Fixture Everyone Fights About

IPC Table E103.3(2) does not list a hose bibb. Appendix E Step 2.1 is blunt: fixture units cannot be applied to constant-use fixtures such as hose bibbs, lawn sprinklers, and air conditioners. Assign gpm and add it after you convert WSFU to demand. That is the IPC walk.

UPC Table 610.3 does list them: 2.5 WSFU for the first hose bibb, 1.0 for each additional when you are sizing building demand (note 8). The fixture branch to each hose bibb is still 2.5. DFU is 0 either way — there is no drain.

The calculator prints UPC hose-bibb WSFU on its own line so you can include it in a UPC city and leave it off in an IPC city. What you must not do is invent 2.5, call it Table E103.3(2), and then wonder why the inspector is looking at Appendix E.

The Bathroom Group Already Counted the Toilet

Two groups plus two WCs plus two lavs plus two showers is not a four-bath house. It is one two-bath house counted twice. The group value exists because diversity inside that room is already in the 3.6 / 5 numbers. Adding the pieces back in is the fastest way to oversize a service and then blame the table.

The other direction is just as common: a powder room (WC + lav, no tub or shower) entered as a bathroom group. IPC §202 requires the tub or shower. A half bath is 2.2 + 0.7 WSFU and 3 + 1 DFU, not 3.6 and 5.

Public Occupancy Is Not a Bigger House

A public flushometer water closet is 10 WSFU. A private flush tank is 2.2. Using the 10 on a residential tank toilet will shove a 1 in house onto a 1-1/2 in row for no reason. Public lavatory 2.0 vs private 0.7. Public shower 4.0 vs private 1.4. If the permit card says dwelling, stay on the private rows. The calculator does not offer the public rows on purpose.

Kitchen Sink + Dishwasher Is Not Automatically 4 DFU

Table 709.1 lists a domestic dishwasher at 2 DFU and a domestic kitchen sink at 2 DFU and a kitchen sink with dishwasher or disposer at 2 DFU. If the dishwasher dumps into the sink tailpiece, the combined row is the one that applies. WSFU still adds 1.4 + 1.4 because they are separate supply loads (the dishwasher is hot-only). Check the box in the calculator only when the dishwasher has its own drain.

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