depending on your room-size and how fast you
can exchange air in that room, you can try a
Ultrasonic Humidifier. These seem to work the
best when it comes to adding some humidity
to a zero percent humidified room

And the only time Humidity sux with the Marijuana
plant is towards the end of flowering, other than
that the plants loves anywhere from 50%-80% RH.

I hope this provides an insite, peace