Wireless wood stove monitor

Wirelessly monitor the combustion gases temperature inside a wood stove’s chimney.

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Wood stoves are a great secondary heating source but care must be taken. It is extremely important that you use your stove in such a way that you do not lower the temperature of the combustion gases inside the chimney too much. Over a period of time, it may result in creosote build-up in the chimney (which could lead a chimney fire). There are two types of chimney thermometers: surface and probe. The latter is used with insulated chimneys. The problem with those thermometers is you have to go near to read them. With probe thermometers (INSIDE the chimney), the gases temperature must be kept between 204 and 482C (400 and 900F). Too low you get creosote build-up, too high you burn the house.

This is a version 2 of my wood stove monitor. On the first version, the thermocouple amplifier breakout board was downstairs and the microcontroller/LCD was upstairs. A >20' cable connected them together and it was a pain in the ass. The thermocouple used was applied to the surface of the chimney and the precision was poor due to lack of good contact.

The new version uses an EGT (Exhaust Gas Temperature) thermocouple and measures the gases inside the chimney. An nRF24L01+ transmits the data from downstairs to a battery operated remote display. The downstairs module has an Adafruit’s RGB backlit LCD which changes color depending of the temperature measured. The thermocouple is interfaced with an Adafruit’s MAX31855 breakout board. This chip has an internal cold-junction temperature sensor for compensation. I’m reading it to get the basement temperature. I’ve installed a thermal shield to prevent any distorted reading due to the radiated heat from the wood stove. That shield will be updated to protect the screw terminal too because it must be at the same temperature of the chip for an accurate compensation.

The remote is equipped with a 2.2" graphic color LCD and a DS18B20 to measure the ambient temperature. The remote is powered by a salvaged LiPo battery and turn itself off after one minute without incoming signal from downstairs.

The power management circuit is a simple high side switch. Thank you Bil Herd for the tutorial!

The main board on both transmitter and receiver are DirtyPCBs I designed as a universal nRF24L01 platform. The microcontroller is a PIC16F690 running PicBASIC code (more on this in the FAQ). You’ll notice on the remote a field named “Log” (“B” on the transmitter). This is the actual log count. This project is part of a bigger one which will be published later: Power Monitor. It’s a simple hack of my smart meter to monitor the household power consumption VS exterior temperature and wood stove usage. It is currently under development. See

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  • The Internet of Wood Stoves (IoWS)!!!

    Michel02/18/2016 at 13:16 0 comments

    Yes! My wood stove monitor’s data is now received by my Power Monitor and pushed to my channel on ThingSpeak.

    The data is transmitted to another address on the same channel. I did it this way because nRF’s pipes work only for one receiver with multiple transmitter. On the Power Monitor side there is another DirtyPCB to handle the nRF24L01+. By using my “nRF platform” 99% of the code was already done! All I had to do is write some code the receive the formatted data on the second serial port available on the Power Monitor. Interconnecting them was a snap: Vcc, Gnd & Data!

    Sneak peek at my power monitor:

  • Crime against humanity corrected

    Michel02/10/2016 at 03:09 0 comments

    [Joakim Soderberg] commented on Hackaday blog entry

    "First of all, that “black on blue” is a crime against humanity (on the display) and should be fixed ASAP."

    I want to apologize to all mankind for this horrible mistake. I should haved done better. Here is the display updated.

    One small step for hacker, one giant leap for mankind.

  • Some data on the operating temperature

    Michel02/08/2016 at 17:43 0 comments

    From what I've found from my research, the probe or surface thermometer must be placed at least 18" (45.72 cm) above the top

    of the stove. There is no indication on the maximum but I think it cannot be placed too far from the stove.

    Data from SBI Heating Accessories for a probe thermometer:

    • 100 - 400°F: Temperature too low. Fire may be dying out. Causes creosote accumulation, smoke or soot.
    • 400 - 900°F: Operating efficiently.
    • 900°F +: Possible overheating. These temperatures may be reached for a brief period during initial firing. Not recommended for prolonged periods.

    Magnetic surface thermometer on a HEPA stove: make sure that the temperature does not exceed 475F (246C).
    Source: Drolet Stove Builder International inc. I have no offical data for the minimum. I have seen between 270F and 475F somewhere.

  • FAQ

    Michel02/06/2016 at 02:50 0 comments

    Q: Why a PICF690 instead of XYZ?

    A: I’m used to PICs. Why I picked this one? I don’t know. I should have picked my favorite one (PIC18F25K22) but I don’t know what I was thinking that day.

    Q: Why PicBASIC?

    A: I’ve learned C with TurboC 20 years ago. It’s been now 20 years I’m programming VBA and VB.NET. I’m just too lazy to go back, don’t have enough time to learn other languages and PicBASIC student version is free so…

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Daniel Grießhaber wrote 02/08/2016 at 13:18 point


great project. I actually do have the same Problem in my chimney from the previous tenant. Could you give me (or anyone who's interested) some data on what temperature range you try to keep?

Another thing: I do have a hole to the chimney in the living room for a second stove. do you think that there is some way to measure the temperature there (around 3-4 m above the exhaust of the stove in the cellar) or is this too far away from the heat source to get a reliable measurement?. Would be great to get it there, because then I could simply put a small circuit inside the bezel that seals the opening (I'm thinking of a simple RGB LED to indicate too cold, too hot, perfect or something like that.

  Are you sure? yes | no

Michel wrote 02/08/2016 at 17:49 point

Hi Daniel,

See projet log for  more data. I don't think you'll get an accruate measurment especially if the chimney is on an exterior wall.

A solution for you could be the circuit downstairs and a simple color serial LCD upstairs: just a 3 wires cable. See for some models.

  Are you sure? yes | no

Daniel Grießhaber wrote 02/08/2016 at 18:35 point

Thank you for your reply.

I'm sorry I totally overread the temperature information on the first time. Thank you.

The chimney basically goes through the middle of our house and has no exterior walls. But this made me thinking: wouldn't it actually be better to measure the temperature right in the middle of the chimney rather than right after the stove? because what actually is important is the temperature of the gases in the chimney?

Yeah I could use a long wire eich would basically be really easy since I could put it in the ventilation shafts of the house but by putting everything in the living room I hoped I could avoid 2 things: running power over a 4m wire (even if its just for some serial LEDs (I have some WS2812 lying around i think) and having to drill another hole inside the exhaust pipe.

I think I just go and buy a temperature probe and measure whats the actual difference between the two spots. I will keep you updated if you like.

  Are you sure? yes | no

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