If the air in the room you are using the incubator is dry, it will certainly effect the humidity of the incubation. If your vents are wide open, that too will lower the humidity.
But on this note, it is best to keep the vents wide open to allow oxygen in the bator, as a lack of oxygen will kill the embryos.
What you can do to keep the humidity stable and high enough is add a wet sponge to the bator. Get a sponge or a piece of a new CLEAN kitchen sponge and wet it down. Wring it out so that it is not dripping wet, but not completely dry either. Put that in right with the eggs. Check the sponge a few times a day, or just monitor the humidity. You may need to re-wet the sponges a couple times a day.