Filtrete 20x25x1 AC Furnace Air Filter, MERV 13, MPR 2200, Elite Allergen, Bacteria & Virus Filter, 3-Month Pleated 1-Inch Electrostatic Air Cleaning Filter, 2-Pack Actual Size 19.69x24.69x0.78 in

[This review was collected as part of a promotion.] I use these with a box fan to bring cool night air into my apartment, while filtering out the smoke particles from the wildfire smoke being blown into my area. They come in a number of sizes that allow you to open a window to a minimum, and keep the worst of the air pollution out. I use a 20x20 and a 20x25 to cover a 20x45 opening. Once, overnight, the air quality unexpectedly went from mod to unhealthy, and my apartment was filled with smoke. Ran my fan with the filter after closing all the windows, and it cleared it up. I advise all my co-workers to use this method, and filters, to protect their lung health.

For those who buy this and don't seem to understand how restrictive these filters can get (higher number=less airflow), here's what you need to know. For furnaces that are 20+ years old, only use UPTO a Merv 8 or MPR 1000 filter, that way the old (or new) blower motor won't be under too much strain and cause issues. If you're furnace is between 10-20 years old, these newer furnaces have much stronger motors and you can safely use UPTO a Merv 12 or MPR 1900 filter without them being too restrictive. Finally, just about anything made in the last 10 years should have no problem running UPTO a Merv 14 or MPR 2800 filter. Something to keep in mind is that this is based on using the most common 16x25x1 filters, if you have enough room to fit a 16x25x4 filter (even if you have to remove the guide bars), then at that point you can safely do Merv 11 or MPR 1200 on a 20+ year old furnace, UPTO Merv 14 or MPR 2800 on 10-20 year old furnace, and UPTO Merv 16 on a furnace made in the last 10 years. As for the very short review of this particular filter, I'd rate it 5/5 stars. MPR 2200 works perfectly on my DIY box fan air filter.