I'm still struggling with the distinction between a standalone sprinkler system and a combined sprinkler/standpipe system on this issue.
NFPA 13's definition of system working pressure specifically excludes pressure supplied through the FDC. If I have a standalone ESFR sprinkler system and the fire department connects a pumper supplying 225 psi through the FDC, that temporary pressure condition doesn't suddenly become part of the system working pressure simply because it exceeds the pressure rating of a sprinkler. To me, that suggests the codes have historically recognized a difference between normal anticipated operating pressure and temporary emergency pressure supplied by the fire department. If that's the case, I'm having trouble understanding why a combined system should be viewed differently. Whether the sprinkler system is standalone or shares a riser with a standpipe, the source of the higher pressure is still the same: temporary fire department pumping through the FDC during an emergency event. The water doesn't know whether it's in a standalone sprinkler system or a combined sprinkler/standpipe system. That's why I keep coming back to the language in NFPA 13 and NFPA 14. It seems difficult to argue that temporary FDC pressure is acceptable to exceed the sprinkler's 175 psi rating in a standalone system, but becomes unacceptable the moment that same sprinkler system shares a riser with a standpipe system. What am I missing? Is there a code provision that specifically requires sprinkler components in a combined system to be protected from anticipated FDC pressures even though NFPA 13 excludes FDC pressure from the definition of system working pressure, or is the intent that temporary fire department pressures are treated differently from normal system operating pressures? Joe Burtell Design Manager D C 406-204-4653 406-861-4507 ________________________________ From: Matt Grise <[email protected]> Sent: Thursday, September 24, 2026 10:59 AM To: Discussion list on issues relating to automatic fire sprinklers <[email protected]> Subject: [Sprinklerforum] Re: Quick question on NFPA 13/14 "System Working Pressure" and FDC-boosted pressure in a combined system CAUTION: This email originated from outside the organization. Do not follow guidance, click links, or open attachments unless you KNOW the content is safe. You might take a look at the sprinkler head listing documents and then contact the manufacturer. If the cut sheets for the sprinklers say that 175 is the max (however they word it) – and the sprinklers are exposed to pressures in excess of 175 (except for hydro testing) – then if a sprinkler fails, even at a time when the pressure is less than 175, I would anticipate you being thrown all of the way under the bus. And probably the bus will be put in reverse, backed up and then pulled forward to run you over again. Not a risk that I would take. Matt From: Fpdcdesign <[email protected]> Sent: Thursday, September 24, 2026 11:52 AM To: Discussion list on issues relating to automatic fire sprinklers <[email protected]> Subject: [Sprinklerforum] Re: Quick question on NFPA 13/14 "System Working Pressure" and FDC-boosted pressure in a combined system Have you looked in the 2022 or 2025 edition to see if the wording changed? Todd Williams Fire Protection Design/Consulting Stonington, CT 860-608-4559 On Sep 24, 2026 at 10:45 AM, <Joe Burtell [MT-BILL]<mailto:[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. [cid:[email protected]] Joe Burtell Design Manager D C 406-204-4653<tel:406-204-4653> 406-861-4507<tel:406-861-4507> 3004 1st Ave South Billings , MT 59101 Office: 406‑247‑0470 www.summitfiresecurity.com<http://www.summitfiresecurity.com> This is a commercial email sent by Summit Companies or one of its affiliates, with an office located at 1250 Northland Drive, Suite 200, Mendota Heights, MN 55120. 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. 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