Can flies enter the house through controlled residential ventilation?

Hello everyone,

for some time now, I have noticed tiny flies (size similar to fruit flies) in the bathroom. At first, I thought they might have come in from outside through the window during cross-ventilation and then removed the flies.

We were away for a few days and accordingly did not open the windows, but there were some flies in the bathroom again. I remove them and the next day there are some again.

So far, there haven't been any of those creatures in the other rooms, but yesterday I saw one in the living area, which could also have escaped from the bathroom.

What do you think, is it possible that they come in through the ventilation?

Thanks

Is it a central or decentralized controlled residential ventilation? Actually, there should be filters in front of both variants.

When we moved in, a few small flies came out of the sockets right away.

Some had nested in a flower pot at our place and then spread throughout the house. Tendency-wise, something often also comes in through fruit.

That they come into the house through a centrally controlled residential ventilation system is rather hard for me to imagine. In this scenario, I consider it most likely that they entered the house while airing and then built a "nest" somewhere (e.g., also in the ventilation ducts).

Sounds like fungus gnats. Usually, they are brought into the house through potting soil and new plants, the little ones are quite persistent. Just put a few yellow sticky traps in the flower pots and that's it ;)

Is it a central or decentralized controlled residential ventilation?

It is a central controlled residential ventilation

Some had nested in a plant pot with us and then spread throughout the whole house. Tendentially, some also come in with fruit.

We have no plants upstairs and only one large one on the ground floor, but the critters are not there. They are exclusively in the bathroom! And there is nothing in/on the fruit or the kitchen either.

In that scenario, I consider it most likely that they came into the house while airing it out and then built a "nest" somewhere (e.g. also in the ventilation ducts).

That could be..

I couldn’t clearly tell whether they really come out of the ventilation duct, but as you describe it, it could be..

Sounds like fungus gnats. Usually you bring them into the house through potting soil and new plants,

I googled them once, they are not fungus gnats..

I’ll take a photo later.