There is no flat price, and any vendor who quotes one before seeing your building is guessing. The cost scales almost entirely with how many points you monitor, then splits into three layers: sensors at each measurement point, the gateways and connectivity that get readings off-site, and a software subscription that stores them and raises alarms. Outlet count drives all three.
That is the honest answer estates and FM managers rarely get. Before you book a demo, this breaks the figure into the lines that actually appear on a quote, shows which are one-off and which recur, and gives you a number you can defend to whoever signs the order.
Why the cost is “per point”, not “per site”
Manual monitoring is priced by labour: someone walks the building each month with a probe. A remote system flips that. You buy a fixed asset at every place you want a reading, plus a service that watches those assets for you. The work that used to be a recurring wage becomes hardware you install once and a subscription you renew.
That is why the single biggest variable is your measurement-point count. A small office with a handful of sentinel taps, one calorifier and a cold-water tank sits a different order of magnitude from a hospital wing with hundreds of outlets and thermostatic mixing valves. The platform and the alerting logic barely change between the two. The sensor count, the number of gateways and the install effort change enormously.
If you have not yet decided how the system would be set up and where probes would sit, Remote water temperature monitoring: benefits and setup is the place to start, because the layout decisions there are what eventually populate the quote.
What you are actually paying for
Here is the cost broken into its real drivers. The pound bands are illustrative planning aids only - rough orders of magnitude, not prices any supplier has quoted you. Use them to spot which line dominates, then get a real quote against your asset register.
| Cost line | What it covers | What moves the number | One-off or recurring |
|---|---|---|---|
| Sensors / measurement points | A probe or transducer at each monitored outlet, TMV blend, calorifier flow and return, and storage tank | Number of points; sentinel-only vs near-full coverage; battery vs hard-wired; accuracy class | One-off (CapEx), often tens to low hundreds of pounds per point |
| Gateways and connectivity | The hubs that collect sensor signals plus the SIM or network link that uploads data | Building size and wall construction; how many gateways give full signal coverage; cellular vs Wi-Fi vs LoRaWAN | Mixed: hardware one-off, data a small recurring fee |
| Software / platform subscription | Live dashboard, threshold alerts, audit-ready reports, record retention | Per-point or per-site licensing; number of user seats; any BMS or logbook integration | Recurring (OpEx), usually annual or monthly |
| Installation and commissioning | Mounting, pairing every device, mapping each point to a named asset, a signal survey | Site complexity; access and working at height; whether work must be out of hours | One-off (CapEx) |
| Calibration and upkeep | Periodic verification, battery replacement, firmware updates | Calibration interval; accuracy requirement; battery vs mains powered devices | Recurring (OpEx), often modest |
Two lines tend to surprise buyers. The first is connectivity in awkward buildings: thick masonry, basement plant rooms and metal risers can mean extra gateways, nudging hardware and survey cost up. The second is commissioning. Pairing a sensor is quick; correctly mapping each one to “Block C, third-floor shower, sentinel” so the data means something is the slow part, and it is what makes the system useful at audit rather than a wall of anonymous numbers.
How outlet count sets the band
A genuinely sentinel-led design monitors a representative subset - the points furthest from and nearest to the heat source on each loop, plus key plant. That keeps the sensor count, and therefore the dominant cost line, proportionate. A probe on every tap in the building is far more expensive and rarely justified outside high-risk healthcare areas.
So the lever you control is coverage. Decide, with your risk assessment, which points truly need continuous data and which are fine on a periodic manual check. The system’s job is to confirm your control measures are holding [3]; it does not need eyes on every outlet to do that. For the coverage questions to put to a vendor, What to look for in a Legionella remote monitoring system: a buyer’s checklist gives the interrogation list.
A quick reality check on what the sensors watch for: HSG274 frames the targets as hot water reaching sentinel taps at around 50 C or above within roughly a minute, and stored cold water staying below 20 C, with sentinel checks commonly done monthly under manual regimes [1][2]. A remote system watches those same thresholds continuously instead of monthly. Your risk assessment, not the device, sets the figures that apply to your building.
CapEx vs OpEx: where the money lands
The split matters for sign-off as much as the total. Sensors, gateways and installation are largely capital - a one-off spend you can depreciate. The subscription, data and calibration are operating cost: a predictable annual line. Many buyers underweight the OpEx and get a nasty renewal surprise, so model at least three years, not just the install.
The trade is OpEx for OpEx. The recurring subscription replaces, in whole or part, the recurring labour of manual rounds. Whether that nets out cheaper depends on building size, how many monthly checks you currently pay for, and what your team’s time is worth - which is exactly the calculation in Technology ROI: cost-benefit of Legionella monitoring systems.
Where the spend pays back
The hardware cost is visible; the savings are quieter. Continuous data removes a large slice of manual monitoring labour and the cost of chasing missed readings. It catches a drifting TMV or a failing calorifier within hours rather than at the next monthly round - the difference between a tweak and a remedial disinfection. And it produces a complete, timestamped record that turns audit prep from a scramble into an export.
None of that shows on the purchase order; all of it shows up in the year-two budget if you skip it. The underlying sensing approach is covered in Smart thermometers: using IoT for Legionella control if you want the technology, not just the invoice.
Building a figure you can defend
To take a credible number to whoever holds the budget:
- Count your measurement points from the asset register, split into “continuous” and “periodic manual” - this sets the sensor line.
- Ask each vendor to itemise hardware, install and annual subscription separately, and to state the per-point cost so you compare like for like.
- Add a connectivity contingency for any plant room or riser likely to need an extra gateway.
- Model three years total, CapEx plus OpEx, against your current manual monitoring spend.
That gives you a defensible total and a clear payback story, not a headline price that falls apart under questioning.
A note on scope
This is general guidance to help you size and compare a purchase. It is not legal, financial or system-design advice, and the cost bands here are illustrative planning aids, not quotations. What you actually need to monitor - and therefore what it costs - must come from a competent, site-specific Legionella risk assessment, not from a price list or this article.
FAQ
Do I need a sensor on every outlet, or just sentinels?
For most buildings a sentinel-led design is proportionate: monitor representative points on each loop plus key plant, and keep the rest on periodic manual checks. Full per-outlet coverage is far more expensive and usually only justified in high-risk healthcare or augmented-care areas. Your risk assessment decides which points qualify.
Is remote monitoring cheaper than manual monthly temperature checks?
It depends on scale. The subscription offsets the labour of manual rounds, so the bigger the building and the more checks you currently pay for, the better it compares. For a very small site with a handful of outlets, manual checks can stay cheaper. Model both over three years.
What’s the ongoing annual cost after installation?
The recurring lines are the software subscription, any connectivity or data fee, and periodic calibration and battery replacement. These are typically modest next to the up-front hardware, but they renew every year, so include them in the business case rather than costing only the first invoice.
Does remote monitoring replace my Legionella risk assessment?
No. It demonstrates your measures are working; it does not assess risk or set your scheme. You still need a current risk assessment and written scheme of control, and the monitoring should be configured to match what they require.
Next step
Pull your water-system asset register, tag every point as “continuous” or “periodic manual”, and total the continuous column. That single figure is the sensor line that dominates your quote - and it is the number to hand each vendor when you ask them to price per point and itemise hardware, install and subscription separately.
Sources
[1] HSE, “Legionnaires’ disease: Technical guidance (HSG274)”. https://www.hse.gov.uk/pubns/books/hsg274.htm [2] HSE, “Hot and cold water systems”. https://www.hse.gov.uk/legionnaires/hot-and-cold.htm [3] HSE, “Testing and monitoring your water system for legionella”. https://www.hse.gov.uk/legionnaires/testing-monitoring-water-system.htm