Sanitary Drain & Stack Sizing Calculator Canada – NPC 2020
Add plumbing fixtures to calculate NPC 2020 sanitary hydraulic load, then size branches, sanitary stacks, and the building drain or sewer from fixture units and slope.
Calculated sanitary hydraulic load
Total hydraulic load
5 FU
Largest fixture / drain minimum
3"
Fixtures / groups entered
2
NPC 2020 horizontal drainage sizing
Size the Branch and Building Drain / Sewer
By default, both lookups use the fixture-unit total above. Enter an override to size a downstream section that serves a different accumulated load.
Sanitary branch — Table 2.4.10.6.-B
NPS 3
Listed capacity: 27 FU · sizing load: 5 FU
Building drain / sewer — Table 2.4.10.6.-C
NPS 4
At 1:50, listed capacity: 240 FU · sizing load: 5 FU
NPC 2020 Article 2.4.9.1 prohibits reducing a sanitary drainage pipe below the largest sanitary drainage pipe that drains into it. The calculator therefore will not return a branch or building drain smaller than the governing fixture/trap connection represented in the fixture list.
Article 2.4.9.4 is being applied: a building drain/building sewer connected to the public sewer downstream of the main cleanout is not less than NPS 4.
NPC 2020 Table 2.4.10.6.-A
Size the Sanitary Stack
A stack must satisfy two limits at the same time: the total fixture units drained to the stack and the maximum fixture units entering from any one storey. If you leave the one-storey field blank, the calculator conservatively assumes the entire stack load enters from one storey.
Sanitary stack — Table 2.4.10.6.-A
Minimum stack size
NPS 3
Table total capacity
102 FU
Stack load: 5 FU
Table one-storey capacity
18 FU
Largest storey load: 5 FU
NPC 2020 Sentence 2.4.10.6.(1) requires the hydraulic load drained to every stack to conform to Table 2.4.10.6.-A. Both the total-stack column and the maximum-from-any-one-storey column must be satisfied.
Where a nominally horizontal offset in a stack is 1.5 m or more, Sentence 2.4.10.6.(2) requires the load served by that offset to conform to Table 2.4.10.6.-B or -C, whichever is less restrictive. Check that offset separately using the horizontal sizing section above.
NPC 2020 is a national model code. Verify the edition and provincial/territorial amendments adopted for the project jurisdiction before final design.
Turn the drainage calculation into a complete plumbing layout
Use the free calculator for section-by-section sanitary checks, then continue into MEPFlow for connected plumbing layout, fixture loads and system sizing.
How the NPC 2020 Sanitary Drain and Stack Sizing Calculator Works
Sanitary drainage sizing in the National Plumbing Code of Canada is a section-by-section process. First determine the fixture-unit load from the plumbing fixtures served. Then select the table that corresponds to the pipe being sized: fixture outlet, branch, stack, or sanitary building drain/building sewer.
Fixture loads and minimum fixture outlet sizes are taken from NPC 2020 Table 2.4.9.3. Sanitary stacks are checked against Table 2.4.10.6.-A using both total stack fixture units and the maximum fixture units entering from any one storey. Horizontal branches use Table 2.4.10.6.-B, while sanitary building drains and building sewers use Table 2.4.10.6.-C.
For building drains and sewers, select the actual design slope. For stacks, enter the total accumulated stack load and the largest load from any single storey. The calculator returns the smallest listed NPS that satisfies the applicable table while respecting the represented fixture and drainage minimum-size constraints.
Calculation basis
Fixture schedule → sanitary FU → stack Table 2.4.10.6.-A / branch Table 2.4.10.6.-B / building drain Table 2.4.10.6.-C
What the Calculator Sizes
- Fixture outlet minimum NPS and drainage fixture-unit load
- Sanitary branch NPS from accumulated fixture units
- Sanitary stack NPS from total FU and maximum FU from one storey
- Sanitary building drain or sewer NPS from fixture units and slope
- Public-sewer NPS 4 minimum downstream of the main cleanout
- Water-closet and trap-driven minimum drain sizes
- Direct fixture-unit overrides for checking specific pipe sections
Important NPC 2020 Checks
- A sanitary drainage pipe cannot be reduced below the largest sanitary drainage pipe that drains into it.
- Drainage piping serving a water closet is not less than NPS 3.
- For stack sizing, both the total-stack capacity and the maximum fixture units drained from any one storey must be satisfied.
- A nominally horizontal offset in a stack that is 1.5 m or more requires a separate horizontal load check under Sentence 2.4.10.6.(2).
- Where a clothes washer does not drain to a laundry tray, NPC 2020 requires an NPS 2 minimum trap inlet and the prescribed standpipe arrangement.
- Building drains and building sewers connected to the public sewer downstream of the main cleanout are not less than NPS 4.
- Continuous-flow fixtures require conversion to fixture units under the NPC procedure before they are added to the sanitary load.
Frequently Asked Questions
How do I size a sanitary drain pipe in Canada using fixture units?
Add the hydraulic load of the fixtures served, then use the applicable NPC 2020 drainage table for that section. Stacks use Table 2.4.10.6.-A, branches use Table 2.4.10.6.-B, and sanitary building drains and building sewers use Table 2.4.10.6.-C with the design slope.
How do I size a sanitary stack under NPC 2020?
NPC 2020 Table 2.4.10.6.-A applies two limits at the same time: the maximum total fixture units drained to the stack and the maximum fixture units drained from any one storey. The selected stack size must satisfy both columns.
Why does the maximum fixture-unit load from one storey matter for stack sizing?
A stack can have an acceptable total building load but still be too small for a large concentration of fixtures entering from one floor. Table 2.4.10.6.-A therefore limits both the total stack load and the load from any one storey.
Does the slope change the required sanitary building drain size?
Yes. NPC 2020 Table 2.4.10.6.-C lists different maximum fixture-unit capacities at slopes from 1 in 400 through 1 in 25. A flatter slope can require a larger pipe and some smaller pipe sizes have no permitted capacity at the flattest slopes.
What is the minimum sanitary drain size for a water closet?
NPC 2020 requires drainage piping serving a water closet to be at least NPS 3. The calculator carries that minimum into the applicable sizing results when a water closet or bathroom group is selected.
Why can the building drain result be NPS 4 even when the fixture-unit table would allow NPS 3?
NPC 2020 Article 2.4.9.4 requires building drains and building sewers connected to the public sewer system downstream of the main cleanout to be at least NPS 4. The calculator applies that rule by default and lets you disable it only for sections where that condition does not apply.
Is this the same as a water-supply WSFU calculator?
No. Sanitary drainage fixture units are used to size drainage piping. Water-supply fixture units are a separate demand method used for domestic water distribution. MEPFlow provides a separate NPC 2020 WSFU calculator for water piping.
Does this replace the National Plumbing Code or provincial plumbing code?
No. NPC 2020 is a national model code and provinces or territories can adopt it with amendments. Use this calculator as a transparent sizing aid and verify the code edition and local amendments applicable to the project.
Engineering References
The calculation basis is taken from the official National Plumbing Code of Canada 2020. Verify the edition and amendments adopted in the project jurisdiction.