Why temperature?

Assuming your burners are controlled by dials, slap a magnet on each of them and set up reed switches.

If you’re gonna disassemble the stove anyway, why not put the sensor on the knob and detect its position?

Not that I’ve done this, but an IR sensor would probably work well.

If it’s a gas burner then it produces CO2 as it operates, right? You could probably mount an ESP32 kit with a CO2 sensor (SGP30) and passive infrared receiver (AM312) over the range to monitor the CO2 level, and also whether anyone is standing at the stove. I didn’t check to see whether these modules were supported directly by esphome, but I’m sure the project either has a compatible module, or you could adapt something from the project to support these modules.

You could then program HA to alert if long term CO2 is elevated and no motion is detected at the range for some time.

Just an idea. I might try tinkering with something similar this weekend. I don’t have the gas sensor, but I’ve been looking for an excuse to order one

Sounds like a simple enough job using a DS18B20 sensor on a cable. They’re digital ambient temperature sensors with ±0.5°C accuracy, and can usually be picked up quite cheaply.

Aside from GND and 5V, they only use a single GPIO pin. As each one has s unique 64-bit address, you can wire more than one to the same GPIO pin without any issues. The only other thing you’ll need is a 4.7K resistor on the 3.3V to the GPIO.

Here in Australia, I got these from Amazon, and wired three up on a single GPIO pin for our lizard’s enclosure. I then wrote a quick and dirty Python script that publishes the temps into MQTT four times a minute, and load them as sensors in HA, to do things with. Admittedly, I’m running them on a Raspberry Pi, but that’s only because I’m also hosting a couple of webcams on it, to keep an eye on the lizard.

You could absolutely do this with an ESP board - esphome has you covered.

Edit: this tutorial will help you get started on how to wire it up.

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do you have a gas meter? surely it would be simpler to capture the operation of the meter either electronically if it’s a smart meter or optically if it has a moving part or dial?

Even if your heating is gas it should be possible to disaggregate that usage by measuring the consumption over a minute or so.

Not sure if I can offer any solution to this, but I would think through how you’ll deal with eliminating false positives like when you’re intentionally cooking something. You might include a PIR sensor to detect whether someone is actually standing at the stove and not send out warnings if movement is detected. Otherwise you’ll get a bunch of notifications about the burners whenever you’re cooking.

No solution for you, but it’s a great idea, and I’ll be watching this space.

Honestly, that should be pretty easy. Throw a thermometer that can connect to HA, put it like on the backsplash or somewhere nearby. Figure out the average temp near there and what it’s like when you’re cooking, then HA should be able to make it pretty easy to check and keep the previous temp(s).

No clue how to do it with an ESP but temp tracking is real common in HA and the automation setup should make that pretty simple to alarm on.

Careful you don’t break gas code since you’re modifying the appliance. Insurance could deem non manufacture approved changes to the appliance and deny any and all claims and whatever governing body that oversees your gas codes could also deem that the appliance is not fit to be used if you ever have a gas tech inspect things.

That said, there is gas floweters that will tell you the gas flow and you can see if the range is on or not. Can’t remember the company that made them as it’s been a few years since I was in the trade and fielding these types of questions from home engineers etc…