A humidifier for adding humidity to an air stream of an HVAC system during a call for humidity includes an air intake configured to fluidically interface with an HVAC duct, a humidifier pad, a valve for controlling delivery of water from a water source to the humidifier pad, and a controller for controlling the valve. The controller may be configured to cause the valve to deliver a variable amount of water over a particular call for humidity. For example, and in some instances, the controller may cause the valve to deliver water to the humidifier pad for substantially less than all of the time for a particular call for humidity.