Duct smoke detectors are the category where orders most often arrive incomplete. The reason is simple: what looks like one device on a drawing is usually three or four separate line items. Here is what actually ships, and what you need to add.
1. The sensor head is often not included
This catches people constantly. Several duct detector housings ship without the sensor. In our own catalog, both the DNR and the watertight DNRW are listed explicitly as head not included. The D4S is listed as sensor only, which is the opposite problem: it is the detector without the full housing assembly.
Before you order, confirm which half you are buying. A housing without a head will not detect anything, and it is a return plus a lost day on site.
2. Conventional or intelligent
Duct detectors split into two families, and they are not interchangeable. The panel decides which one you need.
- Conventional — the D2 is 2-wire photoelectric, the D4120 is 4-wire photoelectric, and the D4120W is the 4-wire version in a NEMA 4 rated enclosure.
- Intelligent / addressable — the InnovairFlex DNR and DNRW, which report individually to an addressable panel.
Putting a conventional detector on an addressable loop, or the reverse, is a design change rather than a substitution. If the submittal names the family, match it.
3. Sampling tube, sized to the duct
The sampling tube is a separate line item and it is sized to the width of the duct it crosses. Ordering the detector and forgetting the tube is the second most common miss.
System Sensor tubes are stocked in a range of lengths: DST1, DST1.5, DST3, DST5 and DST10. On the Gamewell-FCI side we carry metal tubes including ST-3 and ST-5, plus the STN-2.5-L8 and STN-10.0 for the SL series.
Tube length must be matched to duct width using the manufacturer's own sizing table. Do not estimate it. A tube that is too short for the duct will not sample the full cross section.
4. Exhaust tube
The sampling tube brings air in; the exhaust tube returns it. It is a separate part again. We stock the ETX exhaust tube at 1.0 ft.
5. Remote test station
Duct detectors are usually mounted somewhere nobody can reach without a lift: above a ceiling, on a rooftop unit, in a mechanical room. Where the detector is not readily accessible, a remote test station is normally what makes inspection and testing practical, and is commonly required. Confirm the requirement against NFPA 72 and your authority having jurisdiction for the specific installation.
Options we stock:
- RTS151 — remote test station
- RTS151KEY — the same with a key
- RTS2 — multi-signaling duct accessory
- RTS2-AOS — multi-signaling with an add-on strobe
6. Outdoor, wet and washdown locations
A standard duct detector is not built for weather. For exposed installations we stock the DH400OE-1 outdoor enclosure, the D4120W in a NEMA 4 rated enclosure, and the watertight DNRW. Match the enclosure rating to the actual environment, not to the one on a similar job last year.
A quick order checklist
- Detector housing, conventional or addressable, matched to the panel
- Sensor head, if the housing does not include one
- Sampling tube, length matched to duct width
- Exhaust tube
- Remote test station, where the detector is not accessible
- Weatherproof enclosure, if the location calls for it
Confirm on the datasheet
The part number tells you the configuration. It does not give you the data you need to complete the installation. Pull the manufacturer's current datasheet for the exact model and confirm:
- The airflow velocity range the detector is listed for
- Duct width to sampling tube length sizing
- Operating voltage, current draw and relay contact ratings
- Which sensor heads are compatible with the housing
- UL listing and the listed installation orientations
Duct detector performance depends on airflow through the duct. A detector installed outside its listed velocity range may not work as intended, and that is a datasheet question, not a catalog one.
Browse duct smoke detectors and accessories or send us your duct schedule and we will put the line items together.