How to Place Flood, Freeze and Temperature Sensors

Why this matters

A burst washer hose or a frozen supply line does more damage to most houses than any burglar will, and it does it while the owners are at work or away for the weekend. An environmental sensor on a monitored panel turns hours of running water into minutes. But these are the sensors a tech is most tempted to drop on the floor anywhere near the appliance and program as whatever zone type was free, and both shortcuts fail: a probe a few inches from where the water actually runs stays dry while the floor floods, and a flood sensor on a burglary zone type sends police to a leak. This card places each sensor where its water or its cold arrives first, programs it so the station calls the right people, and tests every one through to the station.

The safety note that comes before the floor

These sensors go beside water heaters, sump pumps, washers and in crawlspaces: water and electricity in the same few feet.

• Standing water near an energized appliance or receptacle: do not step into it. De-energize the circuit from a dry location at the panel, or leave it to the customer's electrician where it needs a breaker you cannot reach dry, and do not touch the appliance or its cord until the circuit is off. It stays off until the water is gone and the appliance and receptacle are dry; if either got wet, it stays off until an electrician or the appliance's service tech has checked it.
• A gas water heater or furnace with a gas smell: everyone leaves, no switches touched and no phone used inside, and the gas utility is called from outside.
• Sump pits versus sewage ejector basins. A sump pit holds groundwater. An ejector basin carries sewage, is normally sealed, and can hold hydrogen sulfide; do not open a sealed ejector lid to place a probe. A high-water alarm for an ejector belongs to its own listed float switch, fitted by the plumber.
• Crawlspaces are tight, dark and sometimes wet, with exposed wiring and pests. Look before you crawl, wear knee pads and gloves, and do not crawl through standing water near wiring.

Step 1: put each flood probe where the water arrives first

A flood probe detects water bridging its contacts, so it only sees water that reaches it. The question for each location is where the first water to escape will run, and that is almost always the low point beside the source, not the middle of the room.

• Water heater. On the floor at the base of the tank on the low side of the slab, or inside the drain pan where one is fitted, so a slow leak is caught in the pan before it overflows. A probe under the pan never gets wet until the pan has already overflowed.
• Washer. On the floor behind the machine, under where the supply hoses connect, at the low point. A burst hose sprays behind the machine first.
• Sump. Water in a sump pit is normal, so a probe at the bottom of the pit is a permanent alarm. Fix it to the pit wall above the level at which the pump normally switches on and below the rim, so it gets wet only when the water rises past where the pump should have removed it. That is a failed pump or a power outage, which is exactly what the customer needs to know.
• Sinks. On the cabinet floor at the back corner under the trap and supply valves, where a drip from a fitting lands, not at the front by the doors.
• Other worthwhile spots: behind the dishwasher if the toe kick allows, behind the refrigerator where an ice maker line runs, and in or beside an attic air handler's condensate pan, where an overflow comes through a ceiling.

Keep the probe contacts flat on the surface and clear of anything that can hold a drop of condensation against them.

Step 2: put each freeze sensor where the pipes run coldest

A freeze sensor reports a low temperature at the sensor, not at the pipe, so it has to sit in the same air as the coldest stretch of pipe it protects. The trip point is set or fixed by the maker below normal room temperature and above freezing, so the warning arrives before the water freezes, not after.

• Crawlspaces: near the supply line where it enters through the foundation wall, the coldest stretch.
• Unheated garages, utility rooms and exterior-wall cabinets that carry supply lines.
• Never next to a heat register, a water heater, a furnace, a dryer vent, a refrigerator's warm exhaust, or a sunny window: each of those keeps the sensor warmer than the pipe it is meant to watch.

A temperature sensor with programmable high and low set points does the same job for rooms where the risk is a range rather than freezing: a wine room, a closet holding network equipment, a vacation home's living space. Set the points with the customer and write them on the record.

Step 3: program them so nobody sends police to a leak

Program flood, freeze and temperature sensors on the panel's 24-hour non-burglary zone type, which panels name differently (environmental, supervisory, 24-hour auxiliary). Such a zone reports whether or not the system is armed, does not count as a burglary, and typically sounds the keypads rather than the burglary sirens. The zone types are owned by Zone Types and What Each One Does When Tripped.

At the station, the signal type and the account's action plan decide what happens. A flood or low-temperature signal should go to a call list: the customer, then a second contact who can get to the house, such as a neighbor with a key or a property manager. It should not go to police or fire dispatch. Set the call list with the customer while you are on site, and ask whether they want the station to call at any hour. Most do for a flood. Then check the station shows the action plan on the account, not just the zones.

Step 4: put the account on test and test every sensor through to the station

Each test sends a real environmental alarm, so put the account on test first per How to Put an Alarm Account on Test and Take It Off. Then:

• Flood probes: wet the contacts the way the maker specifies, usually a damp cloth pressed across them. The station should receive a flood or water alarm with the right zone and description, and a restoral once the probe is dried.
• Freeze and temperature sensors: cool the sensor per the maker's test method. Where the maker allows it, a sealed plastic bag around the sensor set in a cooler of ice works, and it takes several minutes; allow the time the maker gives rather than calling it failed early. Do not use freeze spray unless the maker lists it.
• Wireless sensors: test them mounted, in place. A crawlspace, a pit or a cabinet under a sink full of metal pipe can block a signal that was fine at the panel. Signal margin is owned by How to Enroll a Wireless Sensor and Confirm Its Signal.

Worked example: a basement-and-crawlspace house

Split-level house: finished basement with the water heater, washer and sump, a crawlspace under the kitchen wing with the main supply line entering through its foundation wall, and wireless sensors throughout. The log as tested:

ENVIRONMENTAL SENSOR LOG - ACCT 7781
ZONE  SENSOR  WHERE                  STATION   OK
30    flood   water heater pan       FLOOD 30  Y
31    flood   floor behind washer    FLOOD 31  Y
32    flood   sump wall, above pump  FLOOD 32  Y
              on-level, below rim
33    flood   kitchen sink cabinet   FLOOD 33  Y
34    flood   hall bath vanity       FLOOD 34  Y
35    freeze  crawlspace, main line  nothing   N
              at foundation wall
RETEST
35    freeze  same line, 3 ft along  LOW TEMP  Y
              clear of steel duct    35

Five flood probes, five correct arrivals, each tested with a damp cloth and each sending its restoral when dried.

The freeze sensor failed, and the reason was not the sensor. It sat in the ice bag in the crawlspace for the maker's stated time and the keypad showed nothing. Brought out of the crawlspace and chilled beside the panel, it reported at once. So the sensor and its trip point were fine and the transmission was not getting out: the panel's signal reading for that sensor, mounted, was below the shop's margin. A steel supply duct ran directly between the sensor and the receiver two floors up.

The fix kept the sensor on the coldest stretch of pipe rather than moving it to wherever signal was good. Moved 3 ft along the same supply line, still within the first few feet inside the foundation wall, it cleared the duct, its mounted signal reading passed the margin, and the ice-bag retest arrived at the station as a low-temperature alarm on zone 35.

The call list check. With all six zones arrived, the tech asked the operator to read back the account's action plan for a flood signal. It read: call the customer, then the neighbor two doors down, no dispatch. That is the plan the customer chose on site. The account came off test after the station confirmed the last restoral.

What changes the placement

A house with an unfinished basement floor that slopes to a drain. The low point is the floor drain, so water from the water heater may run away from a probe at the tank. Put a probe on the path between the source and the drain.

A vacation or seasonal home. Add a temperature sensor in the main living space, because a furnace failure in winter will freeze every pipe in the house, not just the crawlspace line, and the low-temperature alarm in the living space is the earliest warning of it.

A sensor that can also shut the water off. Some systems pair a flood sensor with a motorized valve on the main. Fitting the valve is plumbing work and goes to a plumber where the locality licenses it; the alarm side is unchanged, and the test should confirm both the station signal and the valve closing.

References

• Sensor and panel manufacturer installation instructions: probe test method, freeze trip point, approved test methods, zone types.
• See related: Zone Types and What Each One Does When Tripped
• See related: How to Enroll a Wireless Sensor and Confirm Its Signal
• See related: How to Put an Alarm Account on Test and Take It Off