Woodstove chimney fire safety is the driving concern behind Oru, a bespoke monitoring system built by Reddit user nas886 that uses stovepipe temperature readings and an ESP32 to keep a woodstove burning in exactly the right range, whether the owner is sitting beside it or not.
The real risk is burning too cold, not too hot
There is a common assumption that the danger from a woodstove comes from running it too fiercely. The more insidious problem, as anyone who has swept a neglected chimney will confirm, is running it too cool. When combustion is incomplete, wood produces creosote, a flammable residue that coats the inside of the chimney flue over time. Given enough accumulation, that creosote can itself ignite, and a chimney fire running inside the flue is a serious threat to the structure of a house. Modern stoves burning properly dried wood make this a remote possibility when operated correctly, but the key phrase is operated correctly, and that requires knowing what the exhaust gases are actually doing.
Oru addresses that directly. A temperature probe sits in the stovepipe itself, monitoring the exhaust gas temperature continuously. Feed the fire well and keep the airflow right, and the reading stays in the safe zone. Let the fire drop too low, and the system flags it before creosote has a chance to accumulate in meaningful quantities.
How the ESP32 and status LED work together
The intelligence in the system comes from an Espressif ESP32 microcontroller, which takes the probe readings and handles the remote notification side of things. When the exhaust temperature falls below the acceptable threshold, the ESP32 triggers a status LED housed inside a separate, custom-built walnut enclosure. The LED changes colour depending on what the stove is doing: one colour signals that the fire needs attention, prompting nas886 to add wood or open the air supply to raise the combustion temperature; a different colour signals the opposite problem, a fire running hotter than it should, at which point restricting the airflow slightly brings things back into line.
The walnut enclosure is a considered touch. Placing the indicator in a handsome, purpose-built unit means it can sit somewhere visible in the living space without looking like a bodged electronics project, which is exactly the kind of detail that makes a home-built system feel finished rather than provisional.
Woodstove chimney fire safety across a wide range of stoves
One of the things that makes Oru genuinely useful across different households is that woodstoves vary enormously. A small, thin-walled stove needs frequent feeding and can overheat quickly if left unattended with the air wide open. A large, high-thermal-mass unit can hold a burn for many hours but requires careful management to stay in the combustion window overnight. Woodstove chimney fire safety considerations shift significantly depending on the size, efficiency, and thermal mass of the unit in question, which means a monitoring approach based on actual exhaust gas temperature, rather than guesswork or a fixed schedule, has genuine utility across the full range.
For those attempting all-night burns in a large stove, the ability to check the indicator without leaving bed has obvious appeal. For those with small, hungry stoves that need feeding every couple of hours, the remote alert takes the anxiety out of stepping away for any length of time.
From custom build to small production run
Nas886 reports finding initial success selling a few of these units in their custom form, and plans to move Oru into further production. The build is also documented well enough that replicating the general approach is within reach for anyone comfortable with microcontroller projects and a bit of woodworking.
The core idea, a probe in the stovepipe feeding temperature data to an ESP32 with a visible indicator, is not conceptually complex, but the execution here into a tidy, sellable package is what sets it apart from a bare breadboard lashed to a thermocouple. Full project details are on Hackaday.
