A landlord with one utility meter for a multi-tenant building has a single number and no fair way to divide it. The tenant running servers pays the same rate per square metre as the office that empties at five. IoT sub-metering closes that gap: a small wireless meter on each tenant's supply measures actual consumption and reports it automatically, so every invoice reflects real usage instead of an estimate. This guide covers how the billing works, which meters suit which buildings, and how the whole layer retrofits into an occupied property without new cabling.
What Sub-Metering Actually Measures
Sub-metering means installing meters downstream of the main utility meter — one per tenant, zone or circuit. The main meter still records what the building draws from the grid; the sub-meters record how that total divides.
An IoT sub-meter adds wireless reporting on top of measurement. Instead of a walk-round with a clipboard, each meter sends its reading over LoRaWAN — a long-range, low-power radio — to a dashboard on a schedule. The full smart metering range is built around this, with meters for electricity, water and gas. The data is cumulative consumption: kilowatt-hours, or cubic metres for water and gas. That running total is what billing is built on.
How the Billing Works
Billing is a subtraction. Take the reading at the end of the period, subtract the reading at the start, apply the tariff. The wireless layer never alters that figure — a meter read remotely is exactly as accurate as one read by hand.
What decides whether you can legally charge for it is the meter's certification. In the EU, billing a tenant for energy requires an MID-approved meter — the Measuring Instruments Directive standard that makes a reading legally valid for commercial billing. The Eastron SDM230-LoRa single-phase meter is an example of a 100 A direct-connect unit carrying that certification.
Choosing the Meter Type
The practical decision is how the meter connects to the supply it measures, because that dictates how disruptive the install is.
| Meter type | How it connects | Best suited to |
|---|---|---|
| Direct-connect | Wired inline with the circuit | New fit-outs and smaller loads |
| CT clamp | Clamps around an existing live cable | Retrofits into occupied buildings |
| Pulse output | Counts pulses from a meter already in place | Adding wireless to existing dumb meters |
| Modbus / M-Bus | Reads a digital meter's data register | Sites with existing smart meters |
For most retrofits, a CT clamp meter is the answer. The Eastron SDM630MCT three-phase CT meter clamps around live cables without an electrician taking the supply down, so tenants never lose power during installation. Where a building already has meters that simply lack reporting, the Acrios wired M-Bus to LoRaWAN converter reads existing M-Bus meters and puts them on the network, and the Milesight UC100 RS485 controller does the same for Modbus meters.
A Real Deployment
A property manager ran a four-storey building with eleven commercial tenants on one electricity meter, splitting the bill by floor area. The ground-floor restaurant — ovens, walk-in fridges, extraction — was quietly subsidised by the upstairs offices, who had started to question their invoices.
The integrator fitted CT clamp meters on each tenant's distribution board with no supply interruption, each reporting over LoRaWAN to a single gateway in the basement riser. Within a month the data showed the restaurant drawing roughly four times the average tenant's electricity.
The next billing cycle charged measured consumption. The disputes stopped, and two tenants who had been overpaying renewed their leases.
What the Network Looks Like
A sub-metering system has three layers: the meters, a gateway that collects their transmissions, and a network server such as The Things Stack or ChirpStack that decodes the data and passes it to a billing dashboard. The meters are provisioned on that server before they go live, registering each device and routing its readings to the right tenant account.
One gateway typically covers a whole building, sometimes a small campus, though thick concrete and basement switch rooms cut range. For larger or multi-site rollouts, the network-planning principles in our guide to LoRaWAN deployment in Europe apply directly to sizing gateways and frequency use.
Where the Regulation Is Heading
Energy costs and EU efficiency rules are moving granular measurement from optional to expected. Commercial building regulation increasingly assumes operators can see and report energy use in detail — the same direction of travel behind the EPBD 2026 BACS requirements for building automation. Sub-metering is the data layer that makes per-tenant reporting and fair cost allocation possible, which is why operators increasingly install it ahead of tightening rules rather than in response to them.
Frequently Asked Questions
Do I need an MID-approved meter to bill tenants?
For legally chargeable billing in the EU, yes. MID approval certifies the meter as accurate enough to base money on. Monitoring-only meters are useful for internal tracking but won't hold up in a billing dispute.
Can I retrofit without rewiring?
In most cases, yes. CT clamp meters fit around existing live cables, and pulse or M-Bus converters read meters already in place, so an occupied building can be metered without new wiring or supply shutdowns.
What happens if a meter loses connection?
A meter with local logging stores readings on board and backfills them when the link returns, so the monthly total stays complete. Confirm local storage is on the datasheet before buying.
Can I sub-meter water and gas as well as electricity?
Yes. Pulse readers and dedicated water and gas meters report cumulative volume over the same network. Many buildings start with electricity — the largest and most uneven cost — then add water once the gateway is in place.
Building Fairer Billing Into Your Property
Sub-metering pays for itself the first time it settles a billing dispute or exposes a costly fault, and it does so without the disruption operators expect from electrical work. CT clamp meters on live circuits, plus battery or self-powered wireless reporting, move an occupied building from estimated billing to measured billing in days rather than weeks.
Moving to Measured Tenant Billing?
The shopioT engineering team helps property managers and integrators specify billing-grade meters, size the gateway coverage, and ship the hardware pre-configured for the network.