I changed the original filter on the 3450i at 48% useage after almost 4 months. This unit is in our sitting room where there is an open fire, primarily burning logs. The filter was coated in a dark grey/black substance, presumably tar particulate. I also started coughing again, so I decided to replace the filter and the result was pretty much instant, my coughing stopped and I enjoyed the clean air once again, so there’s absolutely no doubt in my mind, that the Blueair3450i does exactly what it claims. I have a smaller unit in the bedroom, a 511i and can honestly say, this also is a game changer. I have not replaced the filter on this yet, but expect to do so in the next couple of months. I bought two filters taking advantage of Blueair’s 15% discount.
