Wooden compartment in chimney niche

Google is your friend. It's all already there.

Thanks, I had overlooked that...

looks like this then

Nice idea. However, the wood compartment is already firmly planned with us. Maybe I'll then coat the inside with some kind of clear varnish. Alternatively, paint the inside in wood color or fit in a sheet of metal. We'll see...

What if you use a good facade paint for the compartments? You can probably scrub it off better after the season.

I've thought about that too. But as I said: First, test the thing (trial heating will be around the end of the year) and then we'll see. There are worse problems...