This was purchased based on the recommendations of a major consumer magazine. It was rated number one for HEPA air cleaners. I said this is a little pricey because it is simply a plastic box with 2 filters, a motor and a fan forcing air through. I don't know why air purifiers have to be so expensive. However, this seems to be a quality unit and fairly quiet considering it is moving large amounts of air. This was purchased to help improve the air quality of our house in preparation for the return of our 6 year old grandson who is being treated in a hospital for Leukemia (Our old house is very dusty.). We don't want to take any chances with his health and hope this item will help prevent illness. I have found other units that sell for about double the price of this air purifier and hope this will be adequate. The more expensive units generally have UV lights to kill microorganisms, which this one does not have. This air cleaner has a 1 year warranty on everything except the filters and a 5 year warranty on the motor, if the filters are changed when they are supposed to be. The carbon pre-filter is to be changed every 3 months and the HEPA filter is to be changed every 12 months, under normal use. The unit has indicator lights to tell you when to change the filters. I put a label on the back with the dates the filters were installed and when they are to be changed. According to the consumer magazine, the annual filter cost is $117. The air cleaner has 4 fan speeds: Low, Medium, High and Turbo. On Low, the noise isn't bad at all. The consumer magazine rates the noise on low as very good. The magazine rates the noise on high as good. I have our unit turned on Turbo, and it is rather loud. It is moving quite a bit of air and the noise is to be expected, I suppose. Although I wrote down the dimensions of the unit, it seems larger than I expected it to be. I suppose it needs to be fairly large in order to move and filter as much air as it does. The large size probably keeps the noise level down. The fan seems to be a "squirrel cage" type fan. The manual is available on-line as a PDF file. I would suggest that you look it up and read it before purchase. The manual has all kinds of warnings related to electrical service for the unit. It states that it must be connected to a 15 or 20 amp fused 3 prong grounded outlet. It states that the use of a time-delay fuse or time-delay circuit breaker is recommended. It states that no adapter or extension cord is to be used. This had me afraid that the unit used a great deal of power and I wondered if the electrical service in our old house could handle it. I don't know why the warnings are in the manual. A search of the Internet indicated that the unit uses no more than 115 watts of power (I don't know this for certain). I was able to connect this to one of the few grounded outlets in our old house and thus far have had no power problems. It has a number of LEDs which could bother very sensitive people if used in a bedroom at night. My wife is one of those. The unit has a sleep mode which turns the unit on low for 8 hours and then returns it to the previously selected setting. We may use this in reverse so that the unit (in our living room) is on low during the day and turbo at night. With small children around, we may use the control lock function which locks the controls to prevent the unintended changing of the settings. The air enters the air cleaner from the front and exits from the top. The unit has a carry handle of a sort built into the top. It weighs about 25 pounds. The consumer magazine states that the annual energy cost is about $91, which comes to $7.58/month. This will, of course, vary from area to area. To receive this before our grandson's homecoming, I paid $68.53 for next day delivery. I ordered it on a Sunday and received it on Tuesday. I hated to pay the extra shipping, but felt it was worth it to have it in place before his return. This air cleaner has a "Quiet 30-Day Money-Back Guarantee". If one is not completely satisfied that this unit is quieter than one's previous high-efficiency air purifier, Master Brands HK Limited will take it back and refund the money, less shipping and finance charges. Note: While this is sold as a Whirlpool branded item, it is actually sold by Master Brands HK Limited. Whirlpool has licensed its name for use. So far, I am happy with my purchase and hope it will serve my intended purpose. Update - 09/29/2011: I just changed the pre-filter and found it covered almost completely with dust. A photo of the pre-filter is posted. The pre-filter is removing a great deal of dust from the air. Since installing the air cleaner, the house has to be dusted much less. When I removed the pre-filter, I noticed that the pre-filter doesn't seal very well at the bottom thus allowing dust and other debris to collect on the HEPA filter. It seals much better on the other 3 edges.