I am using a ultrasonic cool mist system, it has a 2.8 gallon tank, it works great, i plumbed 1.5" pvc to the top of the tank, then rap a pipe full width of the top and drill 1/2 inch holes in it, it easily keeps 70% on low and will go up to about 98% on high, i didnt glue any of the pvc so it can be taken apart and cleaned weekly.