To control HVAC without cloud APIs, collect weather observations on your local network, process them with a local controller such as Home Assistant, and send commands through an HVAC interface that also works locally. A weather station’s current readings are observations, not a forecast. And an integration that needs no API key may still depend on an online service.
What counts as local weather data?
There are two different setups that are often described as “local weather.” A station or sensor at your property can measure current conditions and send them over your LAN. Alternatively, an internet service can provide a forecast that your controller stores or uses locally afterward. Only the first avoids relying on an online weather service for the input.
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Home Assistant’s WeatherFlow integration reads data directly from compatible Tempest weather stations over UDP on the local network. Its documentation describes it as a local-only integration and requires the station and Home Assistant server to be on the same subnet. WeatherFlow Cloud is a separate, cloud-based option. See Home Assistant’s WeatherFlow integration documentation.
Station readings describe measured conditions. They do not become a forecast just because Home Assistant represents them as a weather entity. Home Assistant’s Template integration can structure template-provided values, including temperature and forecast fields, as weather entities; it does not generate a forecast from current sensor readings. See the Template integration documentation.
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How do I control my thermostat with local weather data?
Keep the system in three parts: a local weather input, a local automation controller, and a local command path to the HVAC equipment. Each link needs to work without depending on a remote service if internet independence is the goal.
- Choose the weather input. Use a compatible local station for outdoor observations, or read local sensors directly or through MQTT. Decide which measurements the automation actually needs; do not label observations as forecasts.
- Connect the input to the controller. For a compatible Tempest station, Home Assistant’s WeatherFlow integration uses local UDP and requires the station and server to share a subnet. For MQTT sensors, configure the broker, topics, payloads, and availability reporting. Confirm that updates arrive and have timestamps or another way to judge freshness.
- Confirm the HVAC command path. Home Assistant Climate actions can set a target temperature or HVAC mode, but available actions and states depend on the thermostat. Check the device’s exposed controls before designing an automation around a particular mode. See Home Assistant’s Climate documentation.
- Build a bounded rule. Use weather as an input to a modest adjustment or an enable/disable decision, rather than letting it override the thermostat without limits. Set upper and lower bounds, use a deadband or hysteresis to avoid rapid switching, and specify a fallback to the normal thermostat schedule when readings are missing or stale. These are prudent control-design practices, not a setpoint algorithm prescribed by Home Assistant.
- Test the failure cases. Disconnect the sensor or station, stop MQTT updates, and verify what happens if the HVAC interface does not acknowledge a command. Make sure a retained old reading is not treated as current indefinitely.
Which Home Assistant options are local?
| Option | What it provides | Cloud dependence and constraints |
|---|---|---|
| WeatherFlow local integration | Direct observations from a compatible Tempest station | Documented local-only path; Home Assistant and station must share a subnet, with UDP connectivity. Source. |
| Local sensors through MQTT | Sensor values published as MQTT message payloads | Can stay on the LAN if the broker and devices are local. Configure payloads, availability, retained-state behavior, and freshness. Source. |
| Open-Meteo integration | Current conditions and hourly and daily forecasts | Requires internet: it polls the online service every 30 minutes. No account or API key is required, but that does not make it cloud-free. Source. |
| MQTT Climate | HVAC commands and state through MQTT | Marked Local Polling, but the HVAC equipment or a local gateway must support the configured command and state topics. It does not add MQTT support to arbitrary thermostats. Source. |
Does Open-Meteo work without an API key, and is it really local?
Home Assistant’s Open-Meteo integration requires neither an account nor an API key, and supplies current conditions plus hourly and daily forecasts. However, it polls Open-Meteo online every 30 minutes and can become unavailable if the service cannot be reached. It suits a “no credentials” requirement, not a strict “no cloud APIs” requirement.
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Can MQTT control my HVAC if the internet is down?
It can, if the MQTT broker, controller, and HVAC device or local gateway are reachable on the local network and the equipment supports the configured topics. Home Assistant’s MQTT Climate integration is marked Local Polling; the actual commands and state reporting still depend on the interface and its configuration. Check that the HVAC state returns to Home Assistant, rather than assuming a command was applied. See the MQTT Climate documentation.
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What happens when a weather sensor becomes unavailable?
That depends on how the input and automation are configured, so test it rather than assume the last value is safe to use. Home Assistant MQTT sensors can receive the most recent value immediately when the publisher retains it; without a retained message, the initial state is undefined. A retained value can therefore be old even though it appears as a sensor reading. Configure availability and freshness checks, and make the automation fall back to the ordinary thermostat schedule or stop making weather-driven changes when data is stale. See the MQTT Sensor documentation.
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Home Assistant’s REST API can provide an interface to data and services on the local installation, including documented weather forecast retrieval. It is not a weather source: it cannot supply observations or forecasts that the installation does not already have. See the REST API documentation.
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