What is the diameter of the opening for filling the tank?
The opening has a diameter of 1.75 inches.
How long can a heated product be plugged in?
MET Safety Laboratories suggests unplugging the product if you leave your home on an extended vacation, as they do with any electrical appliance. Otherwise, it is designed for 24/7 operation and you can leave it plugged in all day. This item has been certified by MET labs to adhere to strict electrical safety standards. For more information, please visit www.metlabs.com.
Is there an off/on switch?
There is not an off/on switch. It is always on when plugged in.