Old Steamers

Is the DiversiTech WS-1 the Right Condensate Safeguard for Your HVAC System?

Walt Brenner · 22 min read

The DiversiTech/Asurity WS-1 Wet Switch Flood Detector addresses a specific risk: condensate or drain-leak water reaching a monitored area around ducted HVAC equipment. When the detector senses moisture, it changes the state of a wired switch so compatible equipment or an alarm circuit can respond.

This makes the WS-1 different from a battery-powered household leak alarm. It requires compatible power and control wiring, and its actual shutdown behavior depends on how it is integrated with the HVAC system. Placement matters just as much: the detector cannot respond until water reaches its sensing area.

The WS-1 may be worth considering for an air handler in an attic, utility closet, crawlspace, or above finished space. It is not a substitute for a sound condensate drain, an intact pan, or routine inspection.

This guide is a product overview rather than an installation manual. The manufacturer’s product page links to technical and installation documents, but those documents were not available in the supplied evidence for review. Buyers and installers therefore still need to verify current operating power, terminal functions, approved wiring, equipment compatibility, dimensions, expansion limits, listing status, and test/reset procedures before installation.

What the WS-1 Wet Switch Flood Detector Is—and Is Not

The WS-1 is a pan-mounted HVAC flood detector sold under the DiversiTech/Asurity name. It is intended to detect moisture associated with condensate or drain leaks and operate a switch that can shut off connected equipment. It includes visual status indication and built-in TEST and RESET controls rather than functioning only as a local audible alarm. An authorized distributor describes these functions and identifies the product as the Asurity WS-1 Wet Switch Flood Detector. F.W. Webb summarizes the model, shutdown function, controls, and expansion capability.

Its practical job is to monitor a deliberately chosen collection area. That will often be an overflow or secondary pan beneath an air handler, but the correct location depends on where escaping water will actually travel. A perfectly wired detector offers little protection if water leaves the pan or collects elsewhere without reaching it.

The WS-1 should not be confused with a battery-powered water-alarm puck. It needs an electrical supply and integration with an HVAC control circuit. It also does not have a built-in speaker according to one retailer listing. An alarm supplied by others may be supported through the switching arrangement, but the detector itself should not be presented as a standalone audible household alarm.

A concise suitability test is:

  • Potentially suitable: A compatible ducted HVAC system has a secondary pan or another predictable condensate collection point, and the desired response is to interrupt equipment when moisture reaches that location.
  • Potentially unsuitable without additional design: The installation needs a completely standalone alarm, lacks compatible control power, has no predictable collection point, or requires a listing or interface the WS-1 does not have.
  • Needs professional assessment: It is unclear how the air handler, thermostat, condensate pump, alarm panel, or building controls should respond to a trip.

The WS-1 may reduce the chance that an unnoticed condensate problem develops into a larger overflow. It cannot guarantee prevention of water damage, mold growth, drain blockage, pan failure, or HVAC malfunction. It detects moisture at its sensing area; it does not directly identify or correct the underlying fault.

How Moisture Detection Produces an HVAC Shutdown

Air conditioning removes humidity from indoor air. The resulting condensate normally enters a primary pan and leaves through a drain line, either by gravity or through a condensate pump. If that route becomes obstructed, water may accumulate in the primary pan, enter backup containment, or escape around the equipment.

Dirt, debris, mold growth, and spider webs can obstruct an HVAC drain pan or condensate line. Trane also distinguishes between float switches that respond at a set water level and sensor switches that respond when water contacts the sensing area. Trane explains the normal condensate path and these common causes of overflow.

For the WS-1, SecurityBase describes a hydrophilic pad that draws water toward a sensor array by capillary action. The same retailer says integral feet elevate the pad and sensor assembly slightly above the drain pan. The reported operating sequence is therefore:

  1. Condensate escapes or collects in the monitored area.
  2. Water reaches the hydrophilic sensing material.
  3. Capillary action draws moisture toward the sensor array.
  4. The detector trips and changes its switch state.
  5. The connected control or alarm circuit produces the response selected by the installer.
  6. The unit remains tripped until the moisture problem is corrected, the sensing material is dry, and the detector is manually reset.

DiversiTech and its distributors claim that as little as one or two drops of water can activate the WS-1. SecurityBase repeats that claim, but provides no measured drop volume, controlled test method, response-time range, water-quality specification, or environmental limits. SecurityBase describes the hydrophilic sensing construction and the one-to-two-drop activation claim. Treat this as a product sensitivity claim, not a guarantee that every drop landing anywhere in the pan will trigger every unit.

The output side is equally important. The manufacturer identifies the WS-1 as a single-pole, double-throw—or SPDT—switch with normally open and normally closed modes. In plain language, the switch can change between two contact paths when it trips. That gives an installer control options, but it does not determine by itself which HVAC component will stop.

Depending on the approved circuit and equipment design, a trip might interrupt:

  • a thermostat control function;
  • the cooling call;
  • the outdoor cooling equipment;
  • a broader HVAC control circuit;
  • selected equipment rather than the entire system; or
  • a separate alarm or monitoring input.

None of these outcomes should be assumed from the product name. “Shuts off the HVAC” is shorthand for a wiring-dependent control action. The completed installation must be tested to establish what actually stops and what remains energized.

SecurityBase also says the double-throw switching arrangement can interrupt the system while operating an alarm supplied by others. That does not establish universal compatibility with alarm panels, smart-home hubs, or building-management systems. The voltage, input type, switching behavior, supervision requirements, and need for additional interface hardware must be checked for each proposed connection.

WS-1 Specifications: Confirmed Facts, Conflicts, and Missing Details

Published WS-1 listings mix several different kinds of information: detector operating power, switch-contact limits, product measurements, package measurements, product weight, and shipping weight. These figures should not be merged into one supposedly definitive specification.

The manufacturer’s product page is the strongest supplied source for the model identity and listed product attributes. It also links to technical and installation documents, which should be obtained before purchase or wiring. DiversiTech lists the WS-1’s switch configuration, electrical classification, contact rating, controls, dimensions, weight, plenum status, and UL status.

Item Source-labeled information Reader-facing interpretation
Product Manufacturer: DiversiTech/Asurity WS-1 Wet Switch Flood Detector Confirms the model being evaluated
Application Manufacturer: pan-mounted flood detection for ducted HVAC systems A specialized condensate safeguard, not a generic standalone alarm
Switch arrangement Manufacturer: SPDT with normally open and normally closed modes Supports different control responses when properly integrated
Electrical classification Manufacturer: Class 2 A published electrical classification, not a complete wiring instruction
Electrical connection Manufacturer: independently powered The detector needs an electrical supply rather than acting only as a passive mechanical float
Contact rating Manufacturer: 5 A at 250 V A published limit for the switching contacts, not the detector’s stated supply voltage
Operating supply Third-party listings: 24 VAC Must be checked against the current official technical data and instructions
User interface Manufacturer: visual indication plus TEST and RESET controls Current LED meanings and procedures still need verification
Plenum status Manufacturer: plenum rated Separate from an electrical listing or universal code acceptance
UL status Manufacturer: not UL listed UL listing must not be inferred from the plenum statement
Dimensions Manufacturer: 9.6 × 8 × 1.55 inches, described as primary dimensions The page does not clarify whether these are bare-product or packaged dimensions
Dimensions Retail listings: approximately 7.5 × 4 × 1.5 inches A conflicting measurement basis that remains unresolved
Weight Manufacturer: 0.66 lb primary weight Should not be combined with shipping weight
Shipping weight Distributor: 3 lb May include packaging and other shipping materials

Operating power is not the same as contact rating

The distinction between these two specifications is critical:

  • Third-party listings report a 24 VAC operating supply.
  • The manufacturer lists a 5 A at 250 V contact rating.

A contact rating describes a published switching limit. It does not mean the detector electronics should be supplied with 250 V. Conversely, a listing that says 24 VAC does not prove that every nominal 24 V HVAC circuit is compatible or that the contacts can control any desired load without further analysis.

SecurityBase reports 24 VAC operating power and dimensions of 7.5 by 4 by 1.5 inches. It also describes the hydrophilic pad, elevated feet, manual reset, and alarm capability. The retailer’s WS-1 listing provides these third-party operating and construction details. These details identify questions to verify; they should not replace current manufacturer instructions.

Dimensions and weight remain unresolved

Retailers commonly report a body near 7.5 by 4 by 1.5 inches, while the manufacturer page lists primary dimensions of 9.6 by 8 by 1.55 inches. Packaging might explain the difference, but the supplied evidence does not establish that. Anyone working with limited pan clearance should measure the installation area and confirm the product-only dimensions before ordering.

The same caution applies to weight. A manufacturer value of 0.66 lb and a distributor shipping weight of 3 lb do not necessarily measure the same thing. Shipping weight may include packaging or other materials.

What the technical labels do—and do not—tell you

“Class 2” and “independently powered” are manufacturer-listed attributes. In this guide, they can safely be read only as classification and connection labels. Without the current technical documents, they cannot be translated into terminal assignments, conductor choices, or a universal wiring method.

Likewise, “contact loading” means the electrical demand placed on the switch contacts, while “load type” describes the kind of circuit being switched. The published contact rating alone does not establish that a proposed HVAC or alarm circuit is permitted.

Important unresolved details include:

  • warranty terms;
  • expected service life;
  • authoritative product-only dimensions;
  • official terminal functions;
  • whether and how the switching contacts are electrically isolated;
  • compatible equipment and control-board requirements;
  • approved shutdown circuits;
  • maximum numbers and connection arrangements for multiple switches;
  • limits on controlling multiple equipment units;
  • official LED meanings;
  • sensor inspection or cleaning intervals;
  • pad-replacement requirements; and
  • documented performance under contamination, residue, humidity, vibration, or long-term exposure.

These gaps do not establish that the WS-1 is unsuitable. They mean this remains a preliminary product assessment until the current technical data sheet and installation instructions are reviewed.

Finally, “plenum rated” and “UL listed” are separate attributes. A plenum statement does not establish electrical listing, general code compliance, equipment-manufacturer approval, or acceptance by every inspector or procurement authority.

Where a Wet Switch Fits in a Condensate-Protection Layout

An HVAC condensate arrangement may include a primary pan, primary drain, secondary drain, secondary pan, condensate pump, and one or more overflow controls. Not every system uses all of these components.

The primary pan collects water produced during normal cooling, and its drainage route is intended to carry that water away. Where installed, a secondary pan provides backup containment if excess condensate is not contained or removed by the primary arrangement. DiversiTech’s condensate-switch overview discusses primary pans, secondary pans, drain lines, and nearby areas as different monitoring locations and notes that equipment position and orientation affect switch selection. DiversiTech explains these condensate-switch applications and the backup role of a secondary pan.

Possible WS-1 placement concepts include:

  • an overflow or secondary pan beneath an air handler;
  • a permitted point in a pan where water is likely to collect early;
  • another stable, manufacturer-permitted surface on the expected leak path; or
  • several monitored points in a large or segmented area, if the official connection limits allow it.

These are layout concepts, not mounting instructions. The current WS-1 instructions should determine the permitted surface, orientation, clearances, and exact position.

Why pan geometry matters

Water follows slope, seams, obstructions, and the first available outlet. An overflow pan may also flex or sit out of level. A detector installed at the visually convenient end can remain dry while water pools at the opposite end or escapes elsewhere.

Before selecting a location, determine:

  1. Where would water first leave the primary drainage arrangement?
  2. Where is the actual low point of the secondary pan?
  3. Do equipment supports, ribs, or other obstructions divide the water path?
  4. Could water escape over an edge or through a seam before reaching the sensor?
  5. Could service work move, cover, or damage the detector?
  6. Will the detector remain accessible for inspection, testing, drying, and reset?

SecurityBase reports that integral feet raise the hydrophilic pad and sensor assembly slightly above the pan. That construction detail does not prove the detector is immune to corrosion, contamination, or nuisance trips.

Installations with greater consequences

A wet switch may be especially worth evaluating when the air handler is:

  • in an attic above a finished ceiling;
  • in a utility closet adjoining living space;
  • above valuable equipment or stored contents;
  • in a crawlspace where leaks may go unnoticed; or
  • in another location where a small overflow could remain hidden.

These are risk-based examples, not claims of special manufacturer approval for each location. Access, temperature, orientation, pan design, equipment requirements, and applicable codes still matter.

DiversiTech and distributors report that multiple switches can expand coverage or connect to multiple pieces of equipment. The maximum number, permitted connection arrangement, and approved circuits were not established in the supplied evidence and must be confirmed in current manufacturer documentation.

Pre-purchase placement checklist

  • Map the likely condensate leak or overflow path.
  • Find the true collection point rather than assuming the pan is level.
  • Confirm that the proposed surface is stable and permitted.
  • Decide whether one sensing location covers the realistic wet area.
  • Check whether pan ribs or equipment supports interrupt water flow.
  • Preserve access for inspection, functional testing, drying, and reset.
  • Confirm that wiring can be routed without obstructing service.
  • Obtain the current installation instructions before finalizing placement.

Ask an HVAC professional to assess the layout when pan slope, air-handler orientation, limited access, control compatibility, or applicable requirements make the correct location uncertain.

Wet Switch vs. Float Switch vs. Standalone Leak Alarm

A wet switch, float switch, and standalone leak alarm can all respond to unwanted water, but they do not necessarily detect the same condition or produce the same result.

A wet switch reacts when moisture reaches its sensing area. A float switch generally waits for water to rise to a mechanical trip level. A standalone leak alarm commonly detects water locally but may only sound or send a notification.

The principal claimed advantage of a wet switch is response with less accumulated water. That does not establish that wet switches are categorically more reliable. The supplied evidence contains no independent head-to-head testing of response time, missed trips, false alarms, corrosion resistance, contamination tolerance, service life, or lifecycle cost.

Consideration WS-1 wet switch Condensate float switch Standalone leak alarm
Trigger condition Moisture contacts the sensing area Water rises to the float’s trip level Water contacts the alarm sensor
Likely HVAC location Pan or another permitted water path Pan or drain line, depending on design Floor or another monitored surface
HVAC shutdown Possible when correctly integrated into an approved circuit Often possible when designed and wired for HVAC shutdown Usually unavailable unless the alarm has a compatible control output
Notification Visual status; an external alarm may be possible Depends on model and wiring Often local sound or app notification
Reset Reported as manual after the sensor is dry Depends on design and water level Depends on alarm design
Power and wiring Requires compatible power and control wiring Varies by design May be battery-powered or externally powered
Main limitation Cannot respond until water reaches the sensor; shutdown depends on wiring Requires water to reach and raise the float sufficiently May warn without stopping condensate production
Evidence limitation No independent comparative reliability data Performance varies by design and placement Integration capability varies by product

Placement may matter more than the category name. A correctly positioned float can react before a poorly positioned wet switch ever gets wet. Conversely, a wet switch at the pan’s true collection point may trip before the water rises enough to operate a pan-mounted float.

Layered protection can monitor different failure paths. PV Heating, Cooling & Plumbing describes using a wet switch in the pan together with a separate float switch in the drain line. In that arrangement, one device watches the drain-line condition while the other watches for water that has reached backup containment. PV describes this layered wet-switch and drain-line-float approach.

That contractor prefers wet switches, but its conclusion is based on field experience rather than controlled comparative testing. It should not be treated as proof that a wet switch is foolproof or always superior.

Choose according to the drainage layout and desired response:

  • Consider a drain-line control when blockage at that point is the condition that needs detection.
  • Consider a pan sensor when the objective is to react after water enters a monitored pan area.
  • Choose a standalone alarm when notification is sufficient and equipment interruption is unnecessary.
  • Consider layered protection when the consequences justify monitoring more than one failure path.

Installation, Wiring, Testing, and Reset Boundaries

The supplied evidence does not contain the current official wiring diagram, terminal assignments, approved shutdown circuits, or compatibility list. This guide therefore cannot provide a safe universal conductor-by-conductor installation procedure.

The two principal electrical specifications must remain separate:

Electrical concept Published information Required action
Detector operating power Marketplace and retailer listings report 24 VAC Confirm against the current manufacturer technical data and the actual equipment
Switch-contact capacity Manufacturer lists 5 A at 250 V Confirm the load, load type, and permitted circuit; do not treat this as detector supply-voltage guidance

Amazon’s marketplace listing is one third-party source identifying the WS-1 as a 24 VAC product, but marketplace specifications are not a substitute for the manufacturer’s current instructions. The Amazon listing reports 24 VAC operating power.

Before wiring, the installer must establish:

  • the actual HVAC control voltage;
  • the detector’s current operating-power requirement;
  • which equipment or control function should stop after a trip;
  • the contact loading and type of load;
  • whether another relay or interface is required;
  • the HVAC equipment manufacturer’s control requirements;
  • the intended response to loss of detector power or an open conductor;
  • any alarm or building-control input requirements; and
  • the current WS-1 technical and installation instructions.

A 2013 DIY account illustrates why shutdown behavior cannot be inferred from the detector alone. The author reported opening a thermostat common lead, which powered down the thermostat and consequently stopped the fan and condenser. The same account said an alternative arrangement could leave the thermostat and blower operating while disabling only the compressor. The dated DIY account describes these two system-specific outcomes.

These are anecdotes, not wiring recommendations. Opening a particular conductor may be unsuitable for another thermostat, air handler, furnace, heat pump, control board, or communicating system.

Commissioning with the TEST control

The manufacturer confirms that the WS-1 has a TEST control. How it should be operated must be taken from the current instructions. Functional commissioning should establish the real system response rather than merely confirming that an indicator changes.

A qualified installer should verify, as applicable:

  • which equipment stops;
  • which equipment continues operating;
  • whether the thermostat remains powered;
  • whether an external alarm or monitoring input changes state;
  • whether the detector remains locked out as intended;
  • whether RESET restores normal operation; and
  • whether labels or service notes clearly explain the shutdown.

DiversiTech confirms visual status indication, but the supplied current manufacturer information does not define every LED color or pattern. The older DIY account reports green before a trip and red after a trip; that installation-specific observation should not replace current instructions.

Reset boundaries

SecurityBase describes a basic reset sequence: correct the moisture problem, dry the absorbent pad, and press RESET. Because the current official procedure was not reviewed, homeowners should treat this only as general product information and avoid electrical servicing.

No fixed drying time can be promised. The amount of water retained in the pad and surrounding conditions may affect whether the detector is ready to reset.

Do not repeatedly reset the switch simply to restore cooling. A trip may indicate an obstructed drain, failed condensate pump, damaged pan, or another moisture problem requiring correction.

Use a qualified HVAC professional whenever the control circuit, contact loading, approved shutdown strategy, equipment compatibility, or applicable electrical and mechanical requirements cannot be verified.

What to Check After a Trip—or When the Unit Will Not Reset

An unexpected HVAC shutdown may indicate condensate accumulation or a blocked drainage path, but the detector does not diagnose the underlying cause. It indicates that moisture reached its sensing area—or that the associated detector and control circuit require investigation.

A cautious, non-electrical response is:

  1. Observe the status indicator. Note its condition before moving or drying the detector.
  2. Do not bypass the control. Bypassing removes the safeguard while the moisture source may still be active.
  3. Inspect only accessible areas. Look for water in the secondary pan and visible obstruction around the pan, drain outlet, or condensate-pump area.
  4. Arrange correction of the moisture source. Use appropriate HVAC service procedures rather than assuming every trip is a simple clog.
  5. Remove accessible standing water without contacting energized components. If electrical exposure is possible, stop and call a qualified technician.
  6. Follow the current product instructions for drying and reset.
  7. Verify normal operation. Confirm both detector status and the intended HVAC response.

Supported causes of condensate obstruction include dirt, debris, mold growth, and spider webs in the pan or drain line. A condensate-pump problem can also interfere with systems that depend on a pump. The specific cause still requires inspection.

A failed immediate reset may mean that the hydrophilic material remains wet. The 2013 DIY account reported that drying took more than one hour in that particular installation. That account documents an anecdotal drying delay, not an official or typical reset time.

If the visible area appears dry but the detector remains tripped, do not bypass it. A qualified technician should check for retained or hidden moisture and determine whether the problem lies with the detector, wiring, condensate system, or HVAC equipment.

Repeated drying and resetting may restore operation temporarily, but it does not correct a blocked drain, pump problem, or ineffective drainage arrangement.

The supplied evidence establishes no manufacturer interval for sensor cleaning, pad replacement, or periodic functional testing. Detector checks can reasonably be considered alongside routine inspection of the drain and pans, but a contractor’s preferred maintenance schedule should not be presented as a universal WS-1 requirement.

Buying Decision: When the WS-1 Fits and What to Verify First

The WS-1 is a plausible fit for a compatible ducted HVAC system where the goal is to detect moisture at a pan or another defined collection point and initiate an equipment-interruption response.

It is a much less obvious fit when the buyer wants a self-contained audible alarm, cannot identify a reliable water path, or cannot verify how the detector will interact with the HVAC controls.

Product and documentation

Before purchase:

  • Confirm that the item is the DiversiTech/Asurity WS-1.
  • Obtain the current technical data sheet.
  • Obtain the current installation instructions from the documents linked on the manufacturer product page.
  • Confirm the official product-only dimensions if clearance is limited.
  • Check which parts, labels, connectors, and instructions are included.
  • Confirm that the documents apply to the exact product revision being supplied.

Electrical fit

Verify:

  • the current operating-power requirement;
  • the available control voltage at the equipment;
  • the permissible shutdown circuit;
  • the contact load and load type;
  • exactly what should stop after a trip;
  • what happens if detector power is lost or a conductor opens; and
  • compatibility with the air handler, thermostat, furnace, heat pump, control board, or other connected equipment.

Do not confuse the reported 24 VAC supply with the manufacturer’s 5 A at 250 V contact rating. Neither figure, by itself, provides a wiring design.

Placement

  • Map the expected condensate leak path.
  • Identify the true low point or first collection area.
  • Check whether pan ribs, seams, or equipment supports divide the flow.
  • Confirm that the mounting surface and orientation are permitted.
  • Preserve access for service, testing, drying, and reset.
  • Decide whether one detector realistically covers the area.

Alarm and expansion

  • Verify whether external notification is required.
  • Determine whether the alarm or monitoring hardware is included or separate.
  • Confirm the electrical requirements of any alarm panel, smart-home interface, or building-control input.
  • Obtain official limits before connecting several detectors.
  • Confirm the permitted arrangement before using one or more detectors to control multiple equipment units.

Listing and acceptance

The manufacturer lists the WS-1 as plenum rated and not UL listed. Before purchase, determine whether the plenum rating is relevant to the proposed location and whether the absence of a UL listing affects equipment requirements, procurement specifications, local interpretation, or inspector acceptance.

Neither attribute should be interpreted beyond what the manufacturer states. Plenum-rated status does not establish universal code compliance or approval for every installation.

Price and seller information

Observed marketplace and distributor prices vary with seller, stock, and date, so the supplied evidence does not support a stable “typical price.” Recheck the delivered price and verify:

  • the exact model;
  • seller identity;
  • included materials;
  • stock status;
  • shipping cost; and
  • return terms.

Marketplace ratings, review counts, purchase counts, and seller policies are shopping information—not proof of sensitivity, reliability, service life, or resistance to false trips.

Important ownership questions remain unresolved, including warranty, expected service life, pad-maintenance requirements, replacement indicators, false-trip performance, and long-term reliability.

The practical fit test is simple: choose the WS-1 only when current documentation confirms compatible power, acceptable placement, a permitted control circuit, and the intended shutdown behavior. If those points remain uncertain, ask an HVAC professional to select an appropriate wet sensor, float switch, standalone alarm, or layered arrangement.

Frequently Asked Questions

Will the WS-1 always shut down the entire HVAC system?

No. The result depends on how its SPDT switch is integrated with the approved HVAC control circuit. One installation might interrupt a broad control circuit, while another might stop cooling or selected equipment. Functional testing is necessary to confirm what actually stops.

Does the WS-1 really activate with only one or two drops of water?

DiversiTech and distributors claim activation with as little as one or two drops. F.W. Webb repeats that claim for the WS-1, but does not provide a measured volume, controlled test method, response-time range, or environmental limits. F.W. Webb attributes the one-to-two-drop sensitivity claim to the product. Treat it as a marketing sensitivity statement rather than a universal guarantee.

Why will a Wet Switch Flood Detector not reset immediately?

The hydrophilic sensing material may still contain moisture. The reported reset approach is to correct the leak, dry the absorbent pad, and then press RESET. There is no supported fixed drying time. If the detector remains tripped after the visible area is dry, have the moisture source, detector, wiring, and HVAC controls checked rather than bypassing it.

Can the WS-1 replace a condensate float switch?

It may serve as the selected condensate cutoff in some compatible installations, but it is not a universal one-for-one replacement. A wet switch reacts when moisture contacts its sensing area; a float switch reacts after water rises to its trip level. Some systems use both a drain-line float and a pan-mounted wet sensor to monitor different conditions.

Is the WS-1 UL listed because it is plenum rated?

No. DiversiTech lists the WS-1 as plenum rated and not UL listed. The manufacturer’s product page reports those two attributes separately.

The WS-1 offers targeted HVAC condensate protection by sensing moisture and operating a switch that can stop compatible equipment. Its usefulness depends on correct placement, an approved wiring strategy, successful functional testing, and continued maintenance of the condensate system. Verify the current instructions, operating power, contact loading, dimensions, equipment compatibility, expansion limits, and listing requirements before installation, and use a qualified HVAC professional whenever those points cannot be confirmed.