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Legionella quickstart

First building, four sensors, one afternoon

A specific, end-to-end installation for a small hotel or care home. Plan: half a day on site, four sensors, one Mikrotik gateway. Total hardware cost ~€590; SaaS €348 / year. See ROI for the payback math.

Bill of materials

Order before the install day; lead time is 5–10 working days from most EU distributors.

ItemQtyPriceWhere
Efento NS-T-3 LoRaWAN (external probe)4€95Conrad, Distrelec
Pipe contact probe accessory4€30Efento direct
Mikrotik wAP LR8 EU8681€180Conrad
Thermal paste (small tube)1€12any hardware shop
Pipe insulation 30 cm × 41€15any plumber's supply

Sensor map

Place sensors in this order; each is more diagnostic than the previous one.

  1. Storage cylinder top — strap-on contact probe on the uppermost surface of the cylinder, under insulation. Must read ≥ 60 °C.
  2. Storage cylinder bottom — same idea, on the cold-water side of the cylinder. Must read ≥ 55 °C (the dead zone for Legionella is 25–55 °C; 55 °C is the conservative floor).
  3. Ringline supply — clamp on the pipe immediately after the cylinder's hot outlet, after any DVGW-W553 thermometer port if the building has one.
  4. Ringline return — clamp on the pipe immediately before it re-enters the cylinder, after the recirc pump. Must read ≥ 50 °C.

If you have budget for a fifth sensor, put it at the most distant tap (the room farthest from the cylinder, usually a top- floor room). It is the validation that the ringline temperatures translate into a hot tap.

Step-by-step

1 · TTN setup (15 min)

Before going on site:

  • Create a free TTN account at eu1.cloud.thethings.network.
  • Create an Application named after the building, e.g. opensense-hotel-bratislava.
  • Note the App EUI; you will need it for the gateway.

2 · Gateway install (30 min)

  • Power up the Mikrotik wAP LR8. It boots in 30 s.
  • Web UI on http://192.168.88.1, login admin / blank.
  • LoRa → Servers → +: point at TTN EU1 (preconfigured profile).
  • Test by clicking Status; should show connected within 30 s.
  • Place high — on top of the elevator machinery room is ideal for a hotel.

3 · Sensor pair (5 min per sensor)

Each Efento NS-T-3:

  • Read DevEUI, AppEUI, AppKey off the QR sticker.
  • In TTN: Application → + Add end device → Manual → Efento NS-T-3. Enter the three keys, select EU868, LoRaWAN 1.0.3. Save.
  • In OpenSense: + ADD DEVICE → LORAWAN → TTN. Copy the webhook URL.
  • In TTN: Application → Integrations → Webhooks → + Add. Format JSON, paste URL, enable Uplink message only. Save.
  • Power the Efento (hold the magnet on its sensor for 3 s).

You should see a join in TTN within a minute and a measurement in OpenSense within two minutes.

4 · Mount the contact probes (30 min)

Per probe:

  • Wipe the pipe surface clean. Sand light corrosion if any.
  • Apply a thumb-tip of thermal paste to the probe head.
  • Strap to the pipe; tighten the band but do not deform the pipe.
  • Wrap the probe + 10 cm of pipe in insulation foam, tape the seam.
ok
Probe reads within 2 °C of a calibrated reference on the pipe surface
warn
Probe is 3–5 °C off — bad thermal contact, redo with more paste
alarm
Probe reads room temperature — no contact at all; redo the strap-on

5 · OpenSense configuration (15 min)

  • For the storage-top channel: set operating range [60, 85], grace 60 min.
  • For the storage-bottom channel: set [55, 85], grace 120 min.
  • For the supply channel: set [58, 85], grace 60 min.
  • For the return channel: set [50, 85], grace 60 min.

If the building runs a nightly 70 °C disinfection cycle, add a window rule:

windows: [
  { rrule: 'FREQ=DAILY;BYHOUR=3', duration_min: 60, ok_min: 65, ok_max: 78 }
]

6 · Sanity test (10 min)

  • Open a hot tap at the most distant point.
  • Watch the dashboard's distant-outlet channel (if installed) or estimate from the ringline return.
  • Should reach ≥ 50 °C within 30 s.

If it does not reach 50 °C: the building has a real Legionella risk. Engage a plumber. OpenSense has just earned its first quarter.

7 · Subscribe to the quarterly report

Site → Reports → + Subscribe. Template legionella_quarterly. Recipients: building manager, optionally the local water authority. Renders on the 1st of each quarter at 02:00 site-local.

Confirmation

By the end of the install day:

  • All four sensors are reporting in OpenSense.
  • The TTN console shows uplinks every 5 minutes.
  • One test alarm has been fired and acknowledged.
  • The quarterly report subscription is active.

If everything above is true, the installation is complete. The first three months are observation: watch the channels, tune windows for unexpected disinfection cycles, capture any pump-failure events for the plumber.

See legionella-faq for the questions that come up after the install.