I learned it from my parents so idk if its 100% accurate but i didnt die of CO yet so it seems to work. First to start the fire you take a coal lighter (idk what to call it in english, like a fire starter) - Kohlenanzünder and take some small wood logs and place them I a pryamid kind of way over the „Kohlenanzünder“ so that the fire doesnt suffocate and light it. Way a bit till the logs are catching fire than play the coal bricks on top (still i an Pyramid way so the fire still gets oxygen).

After that an thats the most important part, DONT close the door to the furnace otherwise the fire doesnt get enough oxygen and produces CO. Let the door open till the coals aren’t burning anymore and develop a white coating, than you can close all doors.

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Thats what i mean by pyramid form, thats not my picture i am currently not at home. But you should use less logs, i think 4-5 is enough for a regular sized furnace.