A procurement-ready guide for contractors, project engineers, and MRO teams buying fire protection hardware across the United States

Fire department connections (FDCs) are one of those “small” line items that can create outsized problems on a project: mismatched threads, unclear signage, wrong inlet count for the design flow, missing caps, or a configuration that doesn’t match the responding fire department’s hose and coupling practice. This guide breaks down how FDCs work, the common configurations you’ll see in the field, and what to confirm before you release a purchase order—especially when you’re coordinating multi-site builds or export shipments.

What an FDC does (and why the details matter)

An FDC is the fire department’s external access point to supplement water into a building’s fire protection system—typically a standpipe system, a sprinkler system, or a combined standpipe/sprinkler arrangement. When the system is operating (or when crews are preparing for interior firefighting), firefighters connect hose lines to the FDC and pump water into the piping network.

What makes FDC procurement tricky is that the connection point must work reliably under pressure, in real-world conditions, using the couplings and adapters carried by the local responding agencies. That means the “right” FDC is not only about what looks standard on a plan sheet—it’s about compatibility, identification, and durability in the field.

Core specification checklist (before you quote or buy)

Use this checklist to reduce RFIs and change orders:

1) System served: Standpipe, automatic sprinkler, or combined.
2) Inlet count and size: Commonly (2) 2½” inlets on a siamese, but verify total system demand.
3) Thread standard / coupling type: NHS/NST threads, local variants, or large-diameter quick-connect (e.g., Storz) where approved.
4) Body configuration: Wall, freestanding/pedestal, or through-wall with trim; straight or angled inlets for access.
5) Clapper design: Single or double clappers (helps prevent backflow between inlets).
6) Caps and plugs: Thread protection and debris exclusion are not “nice to have.”
7) Signage/marking: Must clearly identify service and (where required) inlet pressure and served areas.

FDC inlet sizing: matching demand flow to inlet capacity

Many U.S. designs still rely on multiple 2½” inlets. A commonly referenced sizing approach in NFPA 14 is one 2½” inlet per 250 gpm of standpipe demand (confirm edition and local amendments with the AHJ and design team). (nfsa.org)

Large-diameter FDCs (such as quick-connect inlets) have been increasingly used where accepted by the authority having jurisdiction (AHJ). Recent industry commentary notes that the 2024 edition of NFPA 14 includes guidance correlating 4″ inlets to 500 gpm and 5″ inlets to 750 gpm for large-diameter fire department connections. (nfsa.org)

Procurement tip: If you’re sourcing for multiple cities (Boise, Salt Lake City, Denver, Phoenix, Seattle), don’t assume “one size fits all.” Confirm the design basis, expected pumper operations, and whether the responding departments prefer threaded 2½” lines, LDH/Storz, or a combination arrangement.

Common FDC configurations (and when each is used)

Configuration What it is Best fit Procurement watch-outs
Siamese (2-way) 2½” Two threaded inlets feeding one system connection, typically with clappers. Many standpipe/sprinkler systems across the U.S. Confirm exact thread (NST/NHS vs local), caps, and signage requirements.
Storz + Siamese combo A large-diameter quick-connect inlet plus (2) 2½” threaded inlets in one body. Facilities where LDH operations are common but threaded compatibility is still desired. Verify Storz size (4″, 5″, etc.), outlet connection to piping, and clapper design. (americanfiresupply.com)
Large diameter quick-connect only Single (or multiple) threadless inlets listed/approved for FDC service. Campuses/industrial sites where LDH is preferred and approved. AHJ acceptance, listed use, flow assumptions, and accessory compatibility.
Wall / flush / freestanding Mounting method impacts access and protection from impact. Driven by site design, bollards, sidewalks, and fire lane layout. Confirm elevation, clearance, and that hoses can be attached without obstruction.
Note: Local fire codes and fire department preferences can override what seems “standard.” Some jurisdictions publish specific connection criteria (for example, thread and clearance requirements) beyond baseline standards—always check local requirements early in design and again before ordering. (sf-fire.org)

Threads, compatibility, and why “NST” isn’t always enough

When teams say “make it NST,” they’re usually referring to National Standard Thread / National Hose Thread used for many fire service connections. But thread compatibility in North America has a long history, and variations still exist. If you’re shipping to multiple U.S. cities or staging for export, confirm what the authority having jurisdiction requires and what adapters the responding department actually carries. (en.wikipedia.org)

Also confirm thread protection and debris protection. Standards language commonly calls for caps to protect threads and prevent debris entry. (firesolution.id)

Step-by-step: How to buy the right FDC (without rework)

1) Confirm what the FDC serves

Standpipe-only, sprinkler-only, or combined systems should be clearly identified. Signage and trim can change based on this decision. (firesolution.id)

2) Validate inlet count against demand (not “habit”)

Verify design flow and how many inlets are required for that demand, then coordinate the physical arrangement (siamese, 3-way, LDH, combo).

3) Lock down thread/coupling requirements early

Confirm whether the local department uses NHS/NST threads or a different local thread. Where local threads do not conform to the common standard, the AHJ can designate what must be used. (firesolution.id)

4) Check access, location, and elevation

FDCs should be located so hoses can be connected without interference and are commonly specified within certain elevation ranges above grade. Confirm site constraints (bollards, landscaping, vehicle routes) before finalizing wall plates and piping rough-ins. (firesolution.id)

5) Don’t treat signage as an afterthought

Permanent signage should identify the system (and where required, pressure and served areas). This is a life-safety labeling requirement and helps crews make correct hook-ups under stress. (firesolution.id)

6) Build a “complete kit” bill of materials

For many projects, a clean procurement package includes: the FDC body, caps/plugs with chains, check/clapper features as specified, escutcheons/trim (if applicable), signage, and any required adapters to match local hose threads.

Quick “Did you know?” facts for project teams

Did you know? NFPA 14 guidance emphasizes that FDCs should be arranged so hose lines can be attached without interference from nearby objects—something that often gets missed when landscaping or security fencing changes late in a project. (firesolution.id)
Did you know? Where an FDC serves multiple buildings or locations, signage should identify what’s being served—critical for campuses and industrial sites. (firesolution.id)
Did you know? Large-diameter quick-connect FDCs have been permitted for years, and recent NFPA 14 cycle updates added more explicit flow guidance for 4″ and 5″ inlets—helpful when you’re deciding between multiple 2½” inlets vs LDH options. (nfsa.org)

United States purchasing reality: standardization vs local requirements

National standards help drive consistency, but procurement teams often support projects across multiple jurisdictions with real differences in fire department operations and fittings. If your organization buys for multiple metros (including Boise, Salt Lake City, Denver, Phoenix, and Seattle), your fastest path is a repeatable verification workflow:

Plan Review: confirm FDC type, inlet count, and signage language on drawings/submittals.
AHJ Confirmation: confirm any local thread/coupling requirements and access/clearance rules.
Field Coordination: confirm final mounting height, bollards, and “no-interference” access before concrete and fencing.
Supply Chain: lock caps, chains, and trim as line items—avoid “value engineering” that creates long-term maintenance pain.
Need help specifying export-ready FDCs and fire protection hardware?
IFW Supply supports procurement teams and project engineers with product cross-referencing, specification review support, and logistics coordination—so what you order is what installs and performs.

FAQ: Fire Department Connections

How many 2½” inlets should an FDC have?
It depends on the system demand and the applicable standard/edition plus local amendments. A commonly cited NFPA 14 sizing approach is one 2½” inlet per 250 gpm of standpipe demand, but your engineer of record and AHJ should confirm the final basis of design. (nfsa.org)
Do FDCs have to be labeled?
Yes—permanent signage is commonly required to identify the system served (standpipe, manual wet/dry, combined standpipe/sprinkler) and may need to indicate inlet pressure and the areas served when multiple buildings are supplied. (firesolution.id)
Can we use Storz (large diameter) inlets instead of multiple threaded inlets?
In many areas, large-diameter quick-connect FDC inlets are permitted where approved by the AHJ and properly listed. Recent NFPA 14 cycle commentary notes added guidance for 4″ and 5″ inlet flow capabilities, which can help with design decisions. Always confirm acceptance and local operational preference. (nfsa.org)
What’s the biggest cause of FDC installation rework?
Mismatched threads/couplings and poor site access are frequent issues—especially when “standard thread” is assumed without confirming local requirements and when landscaping/fencing changes reduce hose hookup clearance. Standards language emphasizes avoiding obstructions and using compatible fittings. (firesolution.id)
What should be included with an FDC to keep it serviceable?
At minimum: caps/plugs and chains for thread/debris protection, durable signage, and any trim/escutcheons required for the mounting style. If you’re sourcing for export or multi-city portfolios, include documented thread/coupling requirements and approved adapters in the procurement package. (firesolution.id)

Glossary (FDC terms buyers and engineers use)

AHJ (Authority Having Jurisdiction): The organization (often the fire marshal or building department) that approves fire protection design and installation in a given area.
FDC (Fire Department Connection): The external connection firefighters use to pump water into a standpipe/sprinkler system.
Siamese: A two-inlet FDC body feeding a single system connection, typically with clappers/check features.
Clapper: An internal check component that helps prevent water from flowing out of an unused inlet when the other inlet is pressurized.
NHS/NST: National Hose Thread / National Standard Thread commonly used for fire hose couplings in many U.S. applications (confirm local requirements). (en.wikipedia.org)
Storz: A quick-connect, quarter-turn coupling often used for large-diameter hose (LDH) operations; sizes vary by jurisdiction and application.
LDH (Large Diameter Hose): High-volume supply hose used for water delivery; often paired with Storz couplings in many areas.

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