// no dedicated hardware needed

A software gateway,
both directions

Q: Can BACManager send BACnet values to MQTT or Home Assistant?

Yes. Set a mapping row's destination to MQTT and the value is published to your broker as a retained topic. With Home Assistant discovery switched on, each row appears in Home Assistant as a sensor, binary sensor, switch or number with its unit. Rows in write mode accept commands back from Home Assistant and write them to the BACnet object at the priority you choose.

Most protocol-converter boxes on the market do exactly one thing: bridge BACnet and Modbus, in one fixed direction, for one price per unit. BACManager's Gateway does both directions from a single Windows PC — read a BACnet controller into a Modbus map a PLC can poll, or read Modbus meters and drives into a real BACnet/IP device a BMS can discover. The same rows can also go BACnet to MQTT — Home Assistant finds them by itself — or into a Siemens S7 data block. No protocol-converter appliance to buy, mount and wire.

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Windows 10/11 · runs in the background · 14-day trial

// the problem

Mixed sites need a bridge somewhere

The AHU and the BMS speak BACnet. The energy meters, VFDs and older equipment speak Modbus. Somewhere between them, something has to translate — and that job usually means an off-the-shelf protocol-converter box: one specific SKU for BACnet/IP-Slave-to-Modbus-Master, a different SKU for the reverse direction, another for MS/TP instead of IP. BACManager replaces that whole shelf of boxes with one PC already running the tool your team uses for commissioning anyway.

// two directions

Pick the direction each point needs

Every mapping row chooses its own source and destination — mix both directions in the same Gateway if a site needs it.

Direction	Source	Exposed as
BACnet → Modbus	A BACnet/IP or MS/TP device, already discovered on the BACnet tab	A shared Modbus TCP map — any PLC polls it like a normal slave
Modbus → BACnet	A Modbus RTU or TCP device — meters, drives, older controllers	A real BACnet/IP device — any BMS discovers it with a normal whoIs
BACnet / Modbus → MQTT	Any of the above, plus the application's own calculated tags	Retained topics on your MQTT broker — Home Assistant discovers each row as an entity
Siemens S7 ↔ both	An S7-1200/1500 data block over PUT/GET	Modbus registers or BACnet objects — or values written into an S7 data block the PLC reads with GET

All of these run from the same Gateway configuration, at the same time, on the same PC.

BACManager Gateway tab configured with a Modbus source endpoint, a read row mapping a Modbus register to a BACnet AI object, a write row mapping a BACnet AV object back to a Modbus register, and the BMS-side BACnet/IP server panel enabled — One Gateway config: a Modbus reading exposed as a BACnet object, and a BACnet write forwarded back to a Modbus register

// how it fits

What you gain over a hardware box

🔌

No appliance to mount

Runs on a Windows PC you already have on site — no DIN-rail converter, no separate power supply, no extra IP address to firewall.

🔒

Priority-aware writes

A write forwarded into a BACnet device uses the real 16-level priority array (default priority 8, Manual Operator) — not a blind overwrite that fights schedules and controllers.

🔊

Runs unattended

Minimizes to the system tray and can auto-start with Windows — it behaves like a background service, not an app someone has to remember to reopen.

📡

BACnet to MQTT

Rows with MQTT as destination are published to any broker — Mosquitto, Home Assistant, Node-RED — with TLS, user and password and an online/offline status topic. Home Assistant discovery turns each row into an entity with its unit, no YAML. BACnet to MQTT guide →

📐

Type and scale conversion

Each row has its own source and destination data type, scale and offset, applied on the way in and reversed on the way back — a meter's 123 reaches the BMS as 12.3, a BMS setpoint reaches the meter as 123.

📋

CSV import and export

Build hundreds of rows in a spreadsheet, BACnet endpoints included, and import them; export a working gateway to reuse on the next site. The whole gateway also travels inside a saved workspace.

// commissioning tool, not just a box

The same PC that discovered the devices

A hardware gateway is configured once, then usually forgotten about — troubleshooting it means dragging out a laptop and a different tool. BACManager's Gateway is a feature of the same application already used to discover, browse and commission the BACnet devices on the job. When a mapping row shows an error, the property browser, the object list and the BACnet activity log are one tab away, not a separate application on a different machine.

// questions

Gateway — FAQ

Does this replace a hardware BACnet-Modbus gateway box?+

For most sites, yes. A PC (or a small always-on Windows box) running BACManager does the same job a dedicated protocol converter appliance does — no separate hardware to buy, wire and maintain, as long as the PC stays powered on.

Does the Gateway run without keeping the window open?+

Yes. It can minimize to the system tray and auto-start with Windows, so it behaves like a background service rather than an application someone has to remember to open.

Are writes from a BMS or PLC safe?+

Yes. Writes forwarded to a BACnet device use the standard 16-level priority array (default priority 8, Manual Operator) instead of a blind overwrite, so they interact correctly with schedules and other controllers already writing to the same point. See our Priority Array guide for how this works.

Can I bridge multiple Modbus devices and multiple BACnet objects at once?+

Yes. The Gateway maps as many source points as needed — Modbus TCP, Modbus RTU, already-discovered BACnet devices, Siemens S7 data blocks and the application's own tags — into a shared Modbus map, a BACnet server device, an S7 data block or MQTT, row by row.

Can BACManager send BACnet values to MQTT or Home Assistant?+

Yes. Set a mapping row's destination to MQTT, enter the broker, and the value is published as a retained topic under your base topic. Switch on Home Assistant discovery and each row appears in Home Assistant as a sensor, binary sensor, switch or number with its unit — no YAML, no cloud. Rows in write mode accept commands from Home Assistant and write them to the BACnet object at the priority you choose.

Does this cost extra on top of the BACManager license?+

No. The Gateway is included in the standard $149 one-time BACManager license — no separate module fee.

A software gateway,both directions