Thank you for your question on the model ZB110H humidity sensing, two speed exhaust fan. We suggest using three switches to operate the ZB110H. One switch will supply the power to the unit so it can run at the low speed. The second switch will power the humidity sensor, so the fan will increase to full speed when there is a rise in humidity. The third switch is a manual switch to turn the fan to high speed when it is needed for odors.