Kelvin

Control your electric radiators and track your electricity cost. Self-hosted.
Control Sauter, Atlantic and Thermor radiators on Cozytouch, and see what your Linky meter says it costs.

What it does

• Rooms. Temperature, what the radiator is doing and until when, and −/+ to change it (in Programme, −/+ sets Confort; Éco has its own control). Tap as many times as you like: Kelvin sends one command 1,5 s after your last tap. A room with two radiators acts as one.
• Weekly schedule. See the week, drag the comfort periods, copy a day to others. Nothing is sent until you press « Envoyer ».
• Temporary heat. Warm one room for a couple of hours (« Chauffer à 22 °C pendant 2 h »); it goes back to what it was doing afterwards.
• Away mode. Turn the whole house down until a date, or « Jusqu’à mon retour » with no end date (ended by « Terminer »), from wherever you are.
• Confirmed changes. A change counts as done only when the radiator confirms it. Pending and failed are shown as such.
• Energy and euros. Your home's consumption from Linky by day, week, month or year, priced with your own tariff: Base, off-peak/peak (HC/HP) or Tempo. See how much goes to the radiators, room by room, and export it as CSV.
• Outdoor temperature (optional). Pick your town and see the temperature outside next to your rooms and your consumption, and how your use changed at equal weather. « Météo et coût » then estimates, with a range, how much you use whatever the weather, how much more each degree colder costs (for the home and each room), what the next 7 days and the month end should cost (forecasts from Météo-France, then ECMWF).
• Alerts. A red Tempo day tomorrow, an EcoWatt warning, a radiator that went offline, new regulated prices, a Linky consent about to expire.
• French or English, switched in Settings without a reload.
• Works on your phone like an app (installable, one dark theme, big touch targets).
• MCP server. Claude and other MCP clients can read your data and suggest ways to pay less. Read-only: they can never change a setting.

Get started

You need: Docker with Compose v2 (amd64 or arm64) and the email and password of your Cozytouch app. For energy and costs, also a free MyElectricalData account (optional).

git clone https://github.com/lborruto/kelvin.git && cd kelvin
cp .env.example .env          # optional: every value has a safe default
docker compose up -d --build

1. Open Kelvin at http://localhost:8070 on the machine that runs it. By default Kelvin is published on this machine only (127.0.0.1:8070); see « Reach it from your other devices » below.
2. Log in with your Cozytouch account (the one the Cozytouch app uses), right away: the first login makes it this Kelvin's home, so whoever reaches an unclaimed Kelvin first can claim it. Everyone in the household then uses the same account. Not on Sauter? Choose Changer under the server name to pick Atlantic or Thermor before that first login.
3. Add Linky (optional):
   • on myelectricaldata.fr, enter your meter number (PDL: the 14 digits on your electricity bill) and accept the Enedis consent; the site then gives you a token;
   • in Kelvin, open Réglages › Linky and enter the PDL and the token, then set your prices in Réglages › Tarif. The first data arrives at the next sync (08:00 or 14:00).

Reach it from your other devices: in .env, set KELVIN_BIND to this machine's LAN address (or 0.0.0.0) and list the names and addresses you will type in KELVIN_ALLOWED_HOSTS, then run docker compose up -d again. KELVIN_PORT changes the port (8070). Better still, put an HTTPS reverse proxy in front and keep the default bind (below).

Host allowlist (recommended): put the names and addresses you type to reach Kelvin in KELVIN_ALLOWED_HOSTS (for example kelvin.lan,192.168.1.10) before the first login. Kelvin then refuses any other host name, which blocks DNS rebinding attacks from web pages you visit. Without it, Kelvin warns in its log.

A folder instead of the Docker volume? On Linux, a bind-mounted data folder must belong to Kelvin's user (uid 10001): sudo chown -R 10001:10001 ./data.

On your phone: open Kelvin in the browser and choose Install app or Add to Home Screen in the browser menu. Installing and the offline shell need HTTPS (or localhost), so put Kelvin behind a reverse proxy first (below).

Just looking? Run the simulator, an invented home with no account needed. Give it its own volume, port and project name, so it never touches a real install (Kelvin refuses to mix simulated and real data in one volume):

KELVIN_FAKE=1 KELVIN_VOLUME=kelvin_demo KELVIN_PORT=8071 COMPOSE_PROJECT_NAME=kelvin-demo \
  docker compose up -d --build

Open http://localhost:8071 and log in with demo@kelvin.local / kelvin. Remove it with the same variables and docker compose down -v.

HTTPS with a reverse proxy

Kelvin itself speaks plain HTTP. For HTTPS on your network, put a reverse proxy in front of it, for example Caddy on the same host:

kelvin.example.lan {
    tls internal                 # Caddy's own certificate for a LAN-only name
    reverse_proxy 127.0.0.1:8070
}

Then tell Kelvin about it:

• KELVIN_ALLOWED_HOSTS=kelvin.example.lan in .env (keep KELVIN_BIND=127.0.0.1: only the proxy reaches Kelvin);
• KELVIN_TRUSTED_PROXIES set to the proxy's address as Kelvin sees it, added under environment: in docker-compose.yml. With Caddy on the host, that is the Docker network's gateway: docker network inspect kelvin_default --format '{{(index .IPAM.Config 0).Gateway}}'. Without it, every client looks like the proxy and shares its login throttle.

Keep the proxy on your network or VPN too: Kelvin is not made to face the internet.

Screens

Weekly schedule	Energy and cost

_{On a phone it installs like an app. All screenshots come from the built-in simulator (invented home, demo data).}

Use it from Claude (MCP)

Kelvin can answer questions like « Why was October more expensive than September? » or « Plan tomorrow's red Tempo day » through your AI assistant. In Kelvin, open Réglages › Compte › Accès MCP, create a token, and copy the ready-made settings it shows (once). For Claude Code:

claude mcp add --transport http kelvin https://kelvin.example.lan/mcp \
  --header "Authorization: Bearer kmcp_…"

Claude Desktop setup, the available prompts and tools, and the security details: backend/README.md › MCP.

Good to know

• Tested on real Sauter radiators (IPALA, HEKLA). Other Sauter, Atlantic and Thermor radiators on Cozytouch are expected to work; other Overkiz servers (Somfy, Hitachi Hi Kumo, Flexom, Nexity Eugénie, Brandt Smart Control, Hexaom HexaConnect, SIMU LiveIn2, Ubiwizz) are experimental. Devices Kelvin cannot drive (water heaters, heat pumps…) are shown read-only, never hidden. Full compatibility table.
• Linky data is a day behind. Enedis publishes yesterday's figures; Kelvin syncs at 08:00 and 14:00 and uses at most 10 of MyElectricalData's 50 daily calls. The daily history arrives at the first sync; the half-hour detail fills in over the following days.
• Your data stays at home. Everything is stored in Kelvin's own data volume. It only talks to Cozytouch and MyElectricalData (for Tempo and EcoWatt it asks for dates only, nothing about you), and, only if you pick a town for the weather, Open-Meteo (your town's position, to about 1 km).
• Keep it on your home network or a VPN (Tailscale, WireGuard…). Never open it to the internet. More in SECURITY.md.
• One server per install. The server (Sauter, Atlantic, Thermor…) is fixed at the first login. To change it, start Kelvin on a new, empty data folder and log in again.
• Unofficial. Kelvin uses the same cloud as the Cozytouch app; if that cloud changes, Kelvin may need an update.

Update and back up

Update to the latest version:

git pull && docker compose up -d --build

The data volume holds your Cozytouch password and Linky token: treat a backup like a password store. This writes it to your home directory, outside the checkout (so git add can never pick it up), readable only by you:

backup="kelvin-backup-$(date +%F).tgz"
docker compose stop
docker run --rm -v kelvin_data:/data:ro -v "$HOME":/backup busybox:1.37 \
  sh -c "umask 077 && tar czf /backup/$backup -C /data . && chown $(id -u):$(id -g) /backup/$backup"
docker compose start

Restore a backup, and a note for rootless Docker

With rootless Docker, drop the && chown … part above: the container's root already maps to your user, and the chown would hand the file to a sub-uid you cannot read.

To restore, set backup to the archive's name in your home directory, then stop Kelvin, replace the volume's content and give it back to Kelvin's user (uid 10001). On a new host, run docker compose create first so the volume exists.

backup="kelvin-backup-2026-10-14.tgz"
docker compose stop
docker run --rm -v kelvin_data:/data -v "$HOME":/backup:ro busybox:1.37 \
  sh -c "rm -rf /data/* /data/.[!.]* && tar xzf /backup/$backup -C /data && chown -R 10001:10001 /data && chmod 700 /data"
docker compose start

Help and docs

I want to…	Read
Change a setting (environment variables, health check, reverse proxy)	backend/README.md › Docker configuration
Know how Kelvin protects my account	SECURITY.md
Use the API or the MCP server	backend/README.md
Hack on Kelvin, run the tests, see how it works	CONTRIBUTING.md
See what changed in each version	CHANGELOG.md
Join in respectfully	CODE_OF_CONDUCT.md
Work on the web app, see every screen	web/README.md
See the design system	DESIGN.md and PRODUCT.md
Read what was verified on real devices and on Linky	docs/

Found a bug, or tried Kelvin on a radiator marked « expected » or « experimental »? Please open an issue with the device's model, never your ids or serial numbers.

Licence

MIT, see LICENSE. Bundled fonts (Geist, JetBrains Mono) are under the SIL Open Font License 1.1; see THIRD_PARTY_NOTICES.md. Weather data by Open-Meteo.com (CC BY 4.0), from Météo-France, ECMWF (IFS forecasts) and Copernicus (ERA5-Land); place search by GeoNames. Kelvin uses Open-Meteo's free API, which is for non-commercial use.

Not affiliated

Kelvin is an independent, unofficial project. It is not made, endorsed or supported by Atlantic, Sauter, Thermor, Cozytouch, Overkiz, Enedis, MyElectricalData, Météo-France or Open-Meteo. Atlantic, Sauter, Thermor, Cozytouch, Overkiz, Enedis, Linky and MyElectricalData are trademarks of their respective owners; they are named here only to say what Kelvin works with.