A procurement-ready guide for contractors, MRO teams, and project engineers buying FDC components across the United States
A fire department connection (FDC) is one of those assemblies that looks simple—until the day it doesn’t fit the responding department’s hose, the caps walk away, or the system demand isn’t clearly marked. For projects with tight schedules, inspections, and turnover packages, getting the FDC details right protects both life safety and timeline. This guide breaks down what to confirm before you buy: inlet configuration, thread standard, check/clapper arrangements, signage, and common spec callouts used for standpipe and sprinkler systems.
What an FDC does (and why the details matter)
An FDC is the listed interface that allows a fire department pumper to pump supplemental water into a building’s fire protection piping (sprinkler, standpipe, or combination systems). In practice, the FDC becomes a “handoff point” between municipal response equipment and your building’s system. That means small specification errors can create big operational issues—especially around thread type, inlet size/count, and accessories that keep the connection usable in an emergency.
For many standpipe/sprinkler applications, NFPA guidance commonly references two 2½-inch inlets with NH internal threaded swivel fittings (2.5-7.5 NH), as specified under NFPA 1963, unless alternative arrangements are permitted. (docinfofiles.nfpa.org)
Core FDC specification choices buyers should confirm
1) Number of inlets: 2-way vs 3-way vs 4-way
The most common configuration on many commercial buildings is a 2-way siamese (two 2½-inch inlets). Larger occupancies, high-rise standpipes, or systems with higher flow demand may use additional inlets or a large-diameter inlet (where accepted by the AHJ and design). If you’re sourcing for multiple sites, standardizing on a single “default” configuration can backfire—confirm the system demand and the design intent per job.
2) Inlet type: NH/NST threads vs Storz
In the United States, NH (also called NST) is widely used as the “fire hose thread” standard referenced under NFPA 1963, and it’s a frequent default for FDC inlets. (docinfofiles.nfpa.org)
Storz (large-diameter, quick-connect) can be specified where local practice supports it and where the needed flow can be met. Storz couplings are used for speed and can be specified in NFPA 1963 for certain sizes. (en.wikipedia.org)
Practical takeaway: thread/coupling mismatches are one of the easiest ways to create an emergency-time problem. If you buy for multiple U.S. regions, confirm the responding department’s preferred connection style and verify what the AHJ expects on the permit set.
3) Body style and mounting: wall, flush, freestanding
FDCs show up as exposed-wall, flush-wall with an escutcheon, or freestanding yard FDCs near fire lanes. This is more than appearance: body style affects corrosion exposure, physical damage risk, and serviceability. Flush-mounted units reduce impact risk but may require more coordination for wall depth and finish.
4) Backflow prevention: clappers, check valves, and drains
Most assemblies include clapper(s) or check components to prevent reverse flow back out of the inlets. Many specs also call for a drain arrangement to reduce trapped water issues in certain climates or configurations. If you’re sourcing parts internationally, be especially careful that the listed configuration matches the submittal requirements and local acceptance.
5) Caps, plugs, chains, and tamper resistance
Caps and plugs aren’t “small parts.” NFPA language commonly expects FDCs to be equipped with approved caps or plugs, secured, and arranged for easy removal by the fire department. (docinfofiles.nfpa.org)
For facilities teams, missing caps often lead to debris ingress, corrosion, and failed inspections. When you issue POs, call out cap material, chain style, and whether you want breakaway chains, locking caps, or other site-specific measures (as permitted by the AHJ).
Quick “Did you know?” FDC facts
NH and NST are commonly used interchangeably in the fire service when discussing standardized fire hose connections. (pdfcoffee.com)
FDC signage expectations can vary by jurisdiction—even when the base standard language is interpreted differently. Always align with the AHJ and project drawings, not assumptions from the last job. (nwfdaz.gov)
Hydrant outlet sizes and threads are often specified to conform to NFPA 1963 (for example, 2½-inch hose outlets and a 4½-inch pumper outlet in some specs), which is why adapter planning matters for multi-site operations. (aspower.com)
A buyer’s step-by-step: how to order the right FDC the first time
Step 1: Identify the served system and label requirements
Start with what the FDC serves: standpipe, sprinkler, or combination. Confirm what the face marking/signage needs to say (e.g., STANDPIPE, AUTO SPKR, COMBINATION) and whether the jurisdiction requires a separate sign with pressure/flow notes. When you source across multiple cities, this step prevents rework at final.
Step 2: Confirm inlet count and inlet standard (threads vs Storz)
For many installations, two 2½-inch NH (2.5-7.5) inlets are a common baseline, but don’t treat it as universal. If a large-diameter Storz inlet is being used, confirm the exact size and local acceptance and ensure compatibility with the response agencies’ equipment.
Step 3: Check the outlet to the system (size and connection type)
The outlet connection to the riser (often flanged) needs to match the contractor’s piping plan. Mismatches here can cause expensive field fabrication. Confirm outlet size, flange drilling standard (if applicable), and whether the check valve arrangement is integral or separate (per the listed assembly and the design).
Step 4: Specify caps/plugs and security details explicitly
Put it in the PO: cap material (brass/aluminum), chain type, and whether you need breakaway or locking features (where permitted). If you maintain critical infrastructure or high-traffic public sites, missing caps can become a recurring maintenance ticket.
Step 5: Plan for adapters when your portfolio spans multiple regions
Even with “standard” threads, incompatibilities and regional variations exist. For multi-state owners/operators, keeping a controlled adapter list (and documenting it) is often cheaper than last-minute expediting. (en.wikipedia.org)
Quick comparison table: common FDC inlet options (U.S.)
Comparison for buyers and spec reviewers
Option
What it looks like on site
Why teams choose it
Watch-outs
Two 2½” NH (NST) inlets
Classic “siamese” FDC with two swivels and caps
Broad U.S. compatibility; common reference under NFPA 1963/NFPA 14 practice (docinfofiles.nfpa.org)
Confirm local thread expectations; keep caps secured
Large-diameter Storz inlet
Single quick-connect inlet (often 4″ or 5″ class)
Fast hookups; useful where departments standardize on LDH (en.wikipedia.org)
Requires alignment with local response equipment and AHJ acceptance
Multi-inlet (3-way/4-way)
More swivels/caps; often used on higher-demand systems
Supports more supply lines and higher flows (design-dependent)
More parts to maintain; signage clarity becomes even more important
Note: Always follow approved submittals, project drawings, and AHJ requirements for the specific site.
U.S. sourcing reality: why “standard” still needs verification
If you buy for multiple markets (Boise, Salt Lake City, Denver, Phoenix, Seattle, and beyond), the safest assumption is that local preferences can differ—even when systems follow the same national codes. Thread compatibility issues and regional coupling practices are well documented in the fire service world, which is why many organizations maintain adapters and clearly document connection standards in their turnover packages. (en.wikipedia.org)
For global procurement teams, that same discipline becomes even more valuable: confirm U.S. compliance needs, then align packing, labeling, and documentation so receiving teams can verify what arrived without guesswork.
Where IFW Supply fits in
IFW Supply is headquartered in Boise, Idaho and supports contractors, distributors, and end users with fire protection, waterworks & irrigation, industrial, and safety products—plus export-ready support for buyers managing complex logistics. (ifwsales.com)
Browse fire protection capabilities: Fire Protection Equipment
Water distribution and accessories: Waterworks & Irrigation
Export coordination and documentation: Export Sales
Product overview for sourcing teams: Products
Need help specifying fire department connections for a multi-site or export project?
Share your submittal requirements (inlet type, mounting, outlet size, finish, caps/chains, markings) and your ship-to locations. The IFW Supply team can help cross-reference components and coordinate procurement-ready documentation.
Tip for faster quotes: include the jurisdiction (city/state), the served system (standpipe/sprinkler/combination), and the inlet standard (NH/NST vs Storz).
FAQ: Fire department connections
Is “NST” the same as “NH”?
In common U.S. fire service usage, NH (National Hose) and NST (National Standard Thread) are often treated as the same standardized fire hose thread naming convention tied to NFPA 1963 practices. Always verify the exact callout on your drawings/submittals. (pdfcoffee.com)
Why do many FDCs have two 2½-inch inlets?
Two 2½-inch inlets are a common arrangement referenced in NFPA 14 language for many installations, unless specific alternatives are met, using NH threaded swivels per NFPA 1963. (docinfofiles.nfpa.org)
Can I replace an NH-thread FDC with a Storz inlet?
Sometimes, yes—but it must be aligned with the AHJ, the design, and the fire department’s equipment. Treat it as an engineered change, not a “like-for-like” swap.
Do FDCs need caps or plugs?
Many codes/standards and inspection expectations call for FDCs to be equipped with approved caps or plugs that are secured and easy for the fire department to remove. (docinfofiles.nfpa.org)
What info should procurement send for an accurate FDC quote?
Provide: served system (standpipe/sprinkler/combination), inlet count and inlet type (NH/NST vs Storz, with exact size), body style (flush/exposed/freestanding), finish/material, outlet size/connection (flanged/threaded), cap/chain requirements, and any signage/marking language required by the jurisdiction.
Glossary
AHJ: Authority Having Jurisdiction—the organization (often the fire marshal/building department) that interprets and enforces code requirements for a specific project.
FDC: Fire Department Connection—a listed assembly that allows fire apparatus to supply water into a building’s fire protection system.
NH / NST: Common terms used for standardized fire hose coupling screw threads widely used in the U.S. and referenced by NFPA 1963.
Siamese: An FDC body with two (or more) inlets that combine into a single outlet to the system.
Storz: A quick-connect, “sexless” coupling style often used for large-diameter hose connections; connects with interlocking lugs rather than threads.