Flying small black insects
The insects in your image appear to be dark-winged fungus gnats.
These gnats can be associated with houseplants that are overwatered. They can also be associated with water leaks from plumbing of all sorts. If flooring is wetted and fungus is growing in the wood, the larvae of these gnats can live in the decaying wood. It is going to take some investigation to find where they may be breeding. Finding the breed site is imperative in removing the population.
If it is overwatered houseplants, allow the soils of the plants to dry to the point that the plants begin to wilt. The larvae cannot survive in the dried soil. There are also some biological products (Bt) that can be added to the soil that will deal with the developing larvae.
Check with your local extension service for more information.