My read is, the boost pressure variable from the FDC is to be excluded. This is the NFPA 13 portion of the system, and governed under such, so 3.3.235 applies. The difference here is the standpipe system. Where the committee dropped the "exclusive of pressure from the fire department connection". On the vast majority of Standpipe systems, (manual) the FDC becomes the system working pressure due to the FDC supplying the system. I'd also imagine they didn't think it would be much of an issue since generally all of the standpipe components are rated to 300 psi.
Jamie Seidl On Thu, Sep 24, 2026 at 10:45 AM Joe Burtell [MT-BILL] < [email protected]> wrote: > I've got a combined sprinkler/standpipe system I'm working through and > want to bounce a question off you, since you're on the NFPA 14 committee. > > THE SCENARIO > > I'm using NFPA 13 (2019) and NFPA 14 (2019). Facts: > > The FDC will be supplied with a pumper truck at 200 psi, as this is a > manual standpipe system. > All pipe, fittings, and valves on the combined riser are rated 300 psi or > greater. > The sprinklers are residential sprinklers, which only come rated to 175 > psi max — there's no higher-pressure listed option to spec around this. > > Since the riser is shared between the standpipe and sprinkler systems, I'm > trying to nail down whether that 200 psi FDC-boosted pressure is something > the sprinkler branch has to be designed/protected against, or whether it's > legitimately excluded from that side. > > THE DEFINITION CONFLICT > > NFPA 13 (2019), 3.3.235 - System Working Pressure: > "The maximum anticipated static (nonflowing) or flowing pressure applied > to sprinkler system components exclusive of surge pressures and exclusive > of pressure from the fire department connection." > > NFPA 14 (2019), 3.3.24 - System Working Pressure: > "The maximum anticipated static (nonflowing) or flowing pressure applied > to standpipe system components exclusive of surge pressures." > > NFPA 14's 2019 definition dropped the FDC exclusion that NFPA 13 still > carries. My understanding is the 2016 edition of NFPA 14 did exclude FDC > pressure, and the exclusion came back (worded differently, as an explicit > inclusion this time) in the 2024 rewrite. So in the 2019 pairing I'm stuck > with, NFPA 13 excludes FDC pressure from working pressure, and NFPA 14 > doesn't carve it back out. > > WHY IT MATTERS HERE > > NFPA 13 also requires sprinkler components to be rated for at least 175 > psi or the max pressure they're actually exposed to, whichever is greater — > separate from how "system working pressure" is defined as a term. On a > shared riser, if the standpipe side gets boosted to 200 psi via the FDC, > that pressure is physically present at the riser regardless of which > standard's definition "counts" it. > > My residential sprinklers are only rated to 175 psi with no higher-rated > alternative. If any part of the sprinkler branch could see more than 175 > psi — even from FDC boost — that looks like a rating gap unless a PRV goes > in on the sprinkler side of the floor control assembly. > > WHAT I'D LOVE YOUR READ ON > > In the 2019 edition pairing, is FDC-boosted pressure meant to count as > part of the standpipe's "system working pressure," given NFPA 14 (2019) > dropped the exclusion language that NFPA 13 (still) has? > For a combined system on a shared riser, does NFPA 13's exclusion of FDC > pressure actually relieve the sprinkler branch from needing protection > against it — or does the "rated for what it's exposed to" requirement > override that once the riser is shared? > Practically: with 200 psi possible at the riser and 175 psi-max > residential sprinklers with no higher-rated option, is a PRV at the > sprinkler takeoff mandatory wherever calculated pressure (inclusive of > anticipated FDC contribution) could exceed 175 psi? Or is there some other > intended mechanism — FDC placard limits, a different assumption about how > the two pressures interact on a shared riser — that I'm missing? > > Any insight into the intent behind the 2019 language change, and how it's > supposed to interact with NFPA 13's exclusion in a combined system, would > really help. > > > Joe Burtell > Design Manager > D > C > > > 406-204-4653 > 406-861-4507 > 3004 > <https://www.google.com/maps/search/3004+1st+Ave+South+Billings+,+MT+59101+Office:+406?entry=gmail&source=g> > 1st > <https://www.google.com/maps/search/3004+1st+Ave+South+Billings+,+MT+59101+Office:+406?entry=gmail&source=g> > Ave > <https://www.google.com/maps/search/3004+1st+Ave+South+Billings+,+MT+59101+Office:+406?entry=gmail&source=g> > South > <https://www.google.com/maps/search/3004+1st+Ave+South+Billings+,+MT+59101+Office:+406?entry=gmail&source=g> > Billings > <https://www.google.com/maps/search/3004+1st+Ave+South+Billings+,+MT+59101+Office:+406?entry=gmail&source=g> > , > MT > 59101 > <https://www.google.com/maps/search/3004+1st+Ave+South+Billings+,+MT+59101+Office:+406?entry=gmail&source=g> > Office: > <https://www.google.com/maps/search/3004+1st+Ave+South+Billings+,+MT+59101+Office:+406?entry=gmail&source=g> > > 406‑247‑0470 <(406)%20247-0470> > www.summitfiresecurity.com > This is a commercial email sent by Summit Companies or one of its > affiliates, > <https://www.google.com/maps/search/3004+1st+Ave+South+Billings+,+MT+59101+Office:+406?entry=gmail&source=g> > with an office located at 1250 Northland Drive, Suite 200, Mendota > Heights, MN 55120 > <https://www.google.com/maps/search/1250+Northland+Drive,+Suite+200,+Mendota+Heights,+MN+55120?entry=gmail&source=g>. > If you no longer wish to receive commercial emails from Summit Companies, > please let us know by contacting us by mail or by email at > privacy@summitcompanies to opt out. > > IMPORTANT: Information contained in this e-mail may be privileged, > confidential, and subject to other protections, including, but not limited > to, the Electronic Communications Privacy Act, 18 U.S.C. 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