Mill Invisible Smart WiFi Panel Heater 400W Gen. 4 (PA400WIFI4)

Mill's 400 W Invisible Gen 4 is a slim electric panel heater for a small room, not a whole-home heating system. The exact white PA400WIFI4 is rated for about 4 to 6 square metres and was listed at NOK 1,449 by Clas Ohlson Norway when checked.

It connects directly through Matter over 2.4 GHz Wi-Fi, without a Mill hub or Thread border router. The important tradeoff is unusually sharp: Mill says Matter and its own app cannot control the heater at the same time. Matterhome has not tested the heater or its integrations.

Choose the control path before setup

Mill's Matter activation guide starts in the Mill app. Create or sign in to a Mill account, open Settings, choose Activate Matter, and follow the prompts for the heater. Mill then emails a Matter QR code and numeric PIN for Apple Home, Google Home, or Alexa. The heater's Wi-Fi button completes the commissioning step when the chosen ecosystem asks for it.

That use of the Mill app is temporary if Matter is the destination. Mill's separate coexistence answer says the two control paths cannot be used together. Once Matter is active, the heater can no longer connect to Mill Cloud.

This choice matters because the product page also advertises weekly schedules, power monitoring, predictive heating, and other app features. Do not assume those Mill app controls remain available in Matter mode. Mill does not publish a platform-by-platform table showing exactly which temperature, mode, energy, and schedule functions Matter exposes.

Apple Home, Google Home, and Alexa are named for this Gen 4 range. SmartThings and Home Assistant are not. They may support the relevant Matter device type, but that generic possibility is weaker than exact-model documentation. Verify the current integration before buying specifically for either platform.

The 400 W size is intentionally narrow

Model identity is easy to blur because Mill sells several Invisible heaters with similar names and different outputs. This guide covers PA400WIFI4, EAN 7090019825308, the white 400 W Gen 4 version sold in Norway and rated for 220 to 240 V. The official range also includes larger models, but their room coverage, dimensions, price, and availability differ.

Mill rates this one for a room of roughly 4 to 6 square metres. The cabinet measures 49.2 by 38.4 by 8.6 centimetres, and a 1.3 metre power cord exits on the right. A wall bracket and screws are included. Open-window detection, child and commercial locks, a claimed maximum surface temperature of 71 degrees Celsius, and an IPX4 enclosure are part of the physical product rather than Matter features.

Mill says the heater is approved for bathroom zone 2. That statement does not overrule local electrical rules, socket placement requirements, or mounting clearances. Confirm the installation with a qualified person when the heater will be near water. A heat-loss calculation is also more useful than a floor-area estimate in a poorly insulated room.

Commission it before mounting permanently

The heater needs 2.4 GHz Wi-Fi. Bluetooth 5.2 assists setup, but it is not the ongoing Matter transport. A compatible Matter controller on the same home network is required; a Thread border router is not.

If the heater is already registered in the Mill app, reset it before activating Matter. Commission it near the intended access point and prove the daily controls before fixing the bracket in its final position. Check temperature changes, heating state, household access, automations, and recovery after a short power interruption. Also confirm that giving up the Mill app's schedules and power view is acceptable.

Returning to Mill Cloud requires removing Matter and performing Mill's documented master reset. The removal guide uses the local gear button to reach rA, followed by YES. Keep the printed label and emailed Matter credentials somewhere recoverable before installation.

Buy it for one compact room

The Clas Ohlson Norway listing offered the exact model with normal shipping when checked. That makes it a current product rather than a certification-only listing. Buyers elsewhere in Europe should still verify the exact model number, plug, voltage, warranty route, and local stock.

Choose PA400WIFI4 when a small room genuinely needs about 400 W and Apple Home, Google Home, or Alexa will be the main control surface. Direct Matter over Wi-Fi is useful here because the heater needs no separate bridge.

Skip it when the room needs more heat, when app energy history and weekly schedules are essential, or when Matter and the Mill app must work side by side. The strongest purchase case is a compact room, a documented ecosystem, and a buyer comfortable committing to one software path.