Having a great success with previous 3D printer debugging, I decided to move it to a completely different level and come with a final solution involving a wall-mounted fan. I am adding a picture of an initial situation which depicts whole enclosed space being padded with a thermal insulation and a light switch located on right.
Not to waste time on this, following is a whole procedure documented in a pictures gallery.
Last picture demonstrates current situation where 305 l/hr (Blauberg BRAVO 150mm White Low Profile Wall / Ceiling Exhaust Fan) fan is mounted together with the light switch being replaced with Fan Speed Controller.
It looks awesome, on the lowest speed that fan is reasonably quiet and first prints show that it does excellent job. Fan’s exhaust goes straight into a cubicle where used to be a central vacuum cleaner with remaining exhaust to the roof. This is not connected, perhaps that would be another stage at the moment when we would start printing with something smelly (ABS).