Having owned an Alien air purifier for years, our unit started making noises. Alen replaced the unit with a newer model since ours was no longer made at no charge! Best warranty of any out there. I decided to add another new 45i for the main area of the house and they are so much nicer looking, quieter and have an Auto mode that senses what speed to run based on air quality. They even have a lights out mode if that bothers you in your bedroom! Best money you will ever spend if you have allergies, pets etc.!