These requirements cover humidifiers rated 600 V or less, and intended to be used in accordance with the National Electrical Code (NEC), ANSI/NFPA 70, and the Rules of the Canadian Electrical Code (CEC), Part 1, C22.1.

These requirements cover humidifiers intended for residential and commercial use. This includes humidifiers of the centrifugal atomizing type, evaporative-media type, water-injection type, steam type, and the like. The humidifiers may be for installation in a room, mounted on a wall or a ceiling, or for duct or plenum mounting.

These requirements apply to equipment that includes an electric heating element to heat air or water, or both.

These requirements do not apply to evaporative coolers that are also intended to be used for cooling.

These requirements do not apply to portable, electrode-type products, such as vaporizers, which are covered by the Standard for Electric Heating Appliances, UL 499, and the CSA Standard for Household Cooking and Liquid-Heating Appliances, CAN/CSA-C22.2 No. 64.