The problem are the spiders. We have the bedroom in the basement and airing is almost impossible, because always nasty giant black spiders sneaking into the room with the windows open. Normally I would have relocated the spiders, but the cellar chute is full of disgusting beasts and given me the meantime been nightmares.
We have therefore only zugenebelt the cellar shaft, before all windows closed and placed on top of the manhole grid a drive to enhance the effect, now, after three days, no more spider can be seen. After misting I sprayed the basement pit with the hose, little queasy is me already, so to use a poison that I freely admit, but I'm glad to have the spider problem solved for now.