Can I mount the Desert Spring Humidifier unit in an attic, ceiling space/crawl space that is unheated?

It depends on the local climate. Care must be taken to ensure the Desert Spring Humidifier is not subjected to freezing as this will damage the unit and may cause leaks. Units located above a ceiling should also include the installation of the overflow line. We highly recommend that you install an overflow line for all installations in an unheated space. There is a location near the float that you can drill out for this purposes (see installation guide). You should also insulate the water line, humidifier and flex duct (regular fiberglass insulation works well), and consider using a hot water supply instead of cold. (Do not place insulation directly against the motor.)