Review on FilterBuy 20X20X1 Pleated Furnace Filters by Shane Jenkins

8 hours after installing this filter with the fan on all the time, the AQI (Air Quality Index) outside was 66 and the AQI inside was 33. It's terrible. Typically, when using a MERV 13 or 14 filter, we expect an 80-90% improvement compared to outside air. This filter only gave us a 50% improvement. I then replaced the FilterBuy filter with an old, dirty filter filter and in just an hour the AQI inside was 8!. I checked the outside air and it was a bit higher - 68. My conclusion: these things are complete garbage. My wife has asthma and we live in smoky California. For us, the use of these filters would be hazardous to our health. I don't know if we can return our 4 pack as one is already being used. But I will try it. If not, 4 new filters will be installed as garbage in the landfill. My recommendation: don't use it. Stay away.