11.1 DFU Values & Load Calculations
Key Takeaways
- 248 CMR 10.15 Table 1 (12/8/2023) assigns drainage fixture units: tank-type toilet 4, valve-operated toilet 6, lavatory with 1-1/4 inch outlet 1, residential kitchen sink 2, residential shower stall 2, bathtub or tub-and-shower unit 2.
- Massachusetts sizes sanitary piping from those Table 1 values plus 10.15(2)(b), not from International Plumbing Code fixture-unit tables or a printed bathroom-group shortcut.
- Continuous or semi-continuous flow from a waste pump, sewage ejector, or similar sewage-discharging device is 2 DFU per gallon per minute, except ejector pumps installed to 10.15(9) Table 5 with a maximum of 20 GPM.
- Unlisted fixtures take the Table 1 size-row values: 1-1/4 inch or less = 1 DFU, 1-1/2 inches = 2, 2 inches = 3, 2-1/2 inches = 4, 3 inches = 5, 4 inches = 6.
- Add every fixture that will actually discharge, including future rough-ins required by 10.15(5), before you open Table 2 or Table 3.
11.1 DFU Values & Load Calculations
Quick Answer: Compute Massachusetts sanitary load from 248 CMR 10.15 Table 1 (effective 12/8/2023). A tank-type toilet is 4 DFU. A valve-operated toilet is 6 DFU. A lavatory with a 1-1/4 inch outlet is 1. A residential kitchen sink (with or without disposer) is 2. A residential shower stall is 2. A bathtub or tub-and-shower unit is 2. Add every fixture, then add 2 DFU per gpm for a sewage pump unless the pump is a 10.15(9) Table 5 ejector at a maximum of 20 GPM. Do not import IPC fixture-unit tables onto this closed-book exam.
The PSI Candidate Information Bulletin dated October 3, 2025 lists Drain, Waste & Vent — Sanitary inside the plumbing written cluster. This section is the load half of that sanitary work: how many drainage fixture units sit on the pipe before you pick a diameter. Independent OpenExamPrep teaching follows 248 CMR 10.15 as posted on Cornell LII and the Mass.gov 12/8/2023 Uniform State Plumbing Code PDF. It is not a Board publication and it does not claim official approval.
248 CMR 10.03 defines a fixture unit as one cubic foot of water drained in a 1-1/4 inch pipe over one minute, and one cubic foot as 7.5 gallons. That definition explains the unit. It does not let you invent loads. 248 CMR 10.15(2)(a) says waste-discharge calculations are computed in drainage fixture units from Table 1: Fixture Unit Values for Various Plumbing Fixtures and from 10.15(2)(b). 10.15(3) then sends those totals to Tables 1, 2, and 3 for pipe size. Chapter 11.2 and 11.3 pick the pipe. This section gets the number right.
Table 1 is Massachusetts, not an IPC appendix
Open Cornell 248 CMR 10.15 and the UpCodes fixture-unit table and copy the printed values. Do not “remember IPC Chapter 7” and hope the numbers match. Massachusetts does not print a single bathroom-group DFU row in Table 1. Add the water closet, the lavatory, and the tub or shower as separate lines. A tank closet is 4 in both many IPC private rows and in Table 1; a flush-valve closet is 6 in Table 1 with no private-versus-public split. A residential dishwasher is 1 DFU, not a second kitchen-sink 2. A residential laundry connection is 3 DFU.
248 CMR 10.15 Table 1 — Fixture Unit Values for Various Plumbing Fixtures (12/8/2023):
| Type of fixture or group of fixtures | Fixture unit value |
|---|---|
| Bathtub or tub & shower unit | 2 |
| Bidet | 2 |
| Dental chair unit or cuspidor | 1 |
| Dental lavatory | 1 |
| Drinking fountain / water station | 1 |
| Dishwasher, commercial | 6 |
| Dishwasher, residential | 1 |
| Floor/trench drain, 2-inch | 4 |
| Floor/trench drain, 3-inch | 5 |
| Floor/trench drain, 4-inch | 6 |
| Kitchen sink, residential (with or without disposer) | 2 |
| Lavatory with 1-1/4 inch outlet | 1 |
| Laundry connection, residential | 3 |
| Laundry / utility sink | 2 |
| Shower stall, residential | 2 |
| Showers (group) per head | 2 |
| Surgeon’s sink | 3 |
| Flushing-rim sink with valve | 6 |
| Service sink with trap standard | 3 |
| Service sink with P-trap | 2 |
| Commercial pot, scullery, etc. (each section) — see Note 1 | 4 |
| Shampoo sink | 2 |
| Toilet, tank type | 4 |
| Toilet, valve operated | 6 |
| Urinal, pedestal, siphon-jet blowout | 6 |
| Urinal, wall lip | 4 |
| Urinal, waterless | 1 |
| Wash sink (circular or multiple), each 20 inches of usable length | 1 |
Sizes for fixtures not listed above: 1-1/4 inch or less 1; 1-1/2 inches 2; 2 inches 3; 2-1/2 inches 4; 3 inches 5; 4 inches 6.
Note 1 sends grease-interceptor sizing to 248 CMR 10.15(1)(b)2.d. / the 10.09 interceptor rules — do not substitute interceptor gallons for Table 1 DFU. Note 2 sends continuous flow to 10.15(2)(b). Note 3 says floor-drain pipe size follows floor area under 248 CMR 10.10(10)(a); Table 1 still gives the DFU once that diameter is known.
A tub-and-shower unit is 2, not 2 for the tub plus 2 for the head. A separate residential stall shower in the same dwelling is another 2. Group showers are 2 per head. Count 20 inches of a circular or multiple wash sink as 1 DFU, the same 20-inch module 10.10 uses for fixture count.
Worked example 1 — Springfield one-family
Fixtures actually installed (no future bath):
| Fixture | Table 1 DFU |
|---|---|
| One tank-type toilet | 4 |
| One lavatory, 1-1/4 inch outlet | 1 |
| One bathtub with shower head (tub & shower unit) | 2 |
| One residential kitchen sink with disposer | 2 |
| One residential dishwasher | 1 |
| One residential laundry connection | 3 |
| House total | 13 |
That 13 DFU is the sanitary load you take to Table 2 for the building drain and to Table 3 for a one- or two-interval stack. It is not an IPC “bathroom group of 5” plus a kitchen. If the owner also wants a separate stall shower, add 2 and the house becomes 15 DFU. If a second tank toilet is roughed for a future bath, 10.15(5) says those future drains count in the final size — add 4, do not wait until the second bath is trimmed.
Kitchen-sink independence is a later fitting rule (10.15(8)(c)): the residential kitchen branch is not less than 1-1/2 inches and the sink shall not waste into a horizontal drain smaller than 3 inches that already receives a flat-bottom fixture. That is pipe arrangement, not a second DFU number. The load for that sink remains 2.
Worked example 2 — Worcester public restroom (flush valves)
| Fixture | Count | DFU each | Subtotal |
|---|---|---|---|
| Valve-operated toilets | 4 | 6 | 24 |
| Lavatories, 1-1/4 inch outlet | 4 | 1 | 4 |
| Wall-lip urinals | 2 | 4 | 8 |
| Branch total | 36 |
36 DFU already exceeds the 3-inch horizontal branch cap of 34 DFU in Table 2 (and that 3-inch row is also not more than four water closets). The branch is 4 inches (Table 2 horizontal-branch column 160 DFU). If someone quotes “flushometer water closet = 4 DFU because it is a public IPC row,” the total becomes a fake 28 and a 3-inch branch looks legal. Table 1 says 6. Use 6.
A waterless urinal is 1 DFU, not 4. Do not “upgrade” it to a wall-lip value. Pedestal / siphon-jet / blowout urinals are 6.
Continuous flow, ejectors, and unlisted outlets
248 CMR 10.15(2)(b): fixture-unit values for continuous or semi-continuous flow into a building sanitary drainage system from a waste pump, sewage ejector pump, or similar device that discharges sewage waste are computed on the basis of two fixture units for each gallon per minute of flow.
Exception: ejector pumps installed in compliance with 10.15(9) Table 5 with a maximum of 20 GPM. That exception is the ordinary single-family sewage ejector: 10.15(9)(b)1. requires a full-size discharge and a minimum 20 GPM pump when the sump receives toilets and other fixtures, and Table 5’s first row is 1 toilet → 20 GPM. Do not add 2 × 20 = 40 DFU on top of the fixtures when that Table 5 / 20 GPM exception applies. A 75 GPM pump serving two or three toilets is not the 20 GPM exception; 2 × 75 = 150 DFU hits the gravity drain that receives the force main unless a Massachusetts PE designs a different 10.15(9) installation.
Scenario. A basement fixture pump rated 12 GPM discharges sewage to the overhead building drain and is not a Table 5 20 GPM ejector. Add 24 DFU to whatever gravity load already sits on that drain. That 24 can be larger than the two basement fixtures the pump serves. Size the receiving gravity pipe for the pump number, not for a “small bathroom.”
Unlisted fixtures: use the outlet-size rows at the bottom of Table 1, not a guess from IPC Table 709.1. A 2-inch custom receptor is 3 DFU. A 3-inch receptor is 5 DFU.
Load calculation is addition, then tables. Wrong Table 1 values make every downstream diameter wrong. 216 DFU on a 4-inch drain is a Table 2 slope question in the next section, not a Table 1 value.
Official resources
- 248 CMR 10.15 Sanitary Drainage System (Cornell) — Table 1, 10.15(2)(b) continuous flow, Table 5 exception
- Fixture Unit Values for Various Plumbing Fixtures (UpCodes) — HTML Table 1
- 248 CMR 10.03 Definitions (Cornell) — fixture unit, 7.5 gallons
- 248 CMR 10.00 Uniform State Plumbing Code (Mass.gov, effective 12/8/2023) — official PDF tables
What drainage fixture-unit value does 248 CMR 10.15 Table 1 (12/8/2023) assign to a tank-type toilet?
How are drainage fixture units computed for a sewage ejector or waste pump discharging into a Massachusetts building sanitary drain under 248 CMR 10.15(2)(b)?
A Springfield one-family dwelling has one tank toilet, one 1-1/4 inch lavatory, one tub-and-shower unit, one residential kitchen sink, one residential dishwasher, and one residential laundry connection. Using only 248 CMR 10.15 Table 1, what is the house drainage load?
A Worcester restroom branch serves four valve-operated toilets, four lavatories, and two wall-lip urinals. What is the 248 CMR 10.15 Table 1 load, and does it fit a 3-inch horizontal branch under Table 2?