Make former heating cellar usable?

Thank you, I will make some calls regarding this :-)

I am glad that someone was able to help you better than I did...

However, I am now interested in what the [Baubiologe] will say to you about it or maybe has even already said.

Unfortunately, I have not learned anything concrete so far. After several phone calls, I only know that the prices for tests vary greatly and the opinions on the question "Is it sensible to have it tested" also vary greatly...

In my opinion, this is somehow the most annoying thing about these matters... How much the individual building biologists charge for it or how many liberties they take here.

You kind of know that you are dependent on them...

The tanks including their contents have only been outside for 10 days – the question is also whether you can rely on your nose regarding indoor air pollution? Or are there maybe measuring devices for something like that?

With the old single-walled plastic tanks, hydrocarbons could diffuse through the wall, causing the odor. With the newer ones marked with the "Proofed Barrier" sign, it has improved. With the double-walled tanks (with the sign), you smell even less. It will take some time until the room is odor-neutral again. To speed it up, remove the oil tank room paint that the oil drip pan was painted with. The concentrations that have accumulated in the wall plaster over the years need their time or some mechanical assistance. The more you remove from the walls, the faster the smell will be gone. Ventilate a lot. It is common, especially with the formerly larger systems where the tanks had to be placed in a separate room, for the rooms to be converted for other purposes.