>>519353605
It's true.
It's an old-timey fireplace like the one in the OP pic. The municipal govt implemented an ordinance that limits the amount of soot (Feinstaub) that a fireplace may produce. Only expensive modern ovens can pass this test because theay already have integrated filters.
But the real problem is the Schornsteinfeger. He arrives once every year to every German household to inspect the heating systems and chimneys. So if you keep using the fireplace, he will notice this during the inspection and then report it to the authorities.
You can not refuse entry to your home to the Schornsteinfeger. If you do, you'll be fined and eventually he will bring the polic to force entry into your property.

I swear to Christ I am not making this up.