My HVAC system uses the cheap 1″ fiberglass filters. I have noticed that I am waking up more and more with a mild sore throat, mucus, post nasal drip, etc. I am looking into air purifiers for the bedroom, but also thinking that those cheap fiberglass filters are doing nearly nothing when it comes to filtering.

I have one return in the ceiling downstairs, and one upstairs in an 1850sqft house. One is 14×25″ and one is 20×25″. It would not surprise me at all if this was undersized…the builder was cutting every corner he could. I live in the Charleston, SC area, so the AC runs over half the year, and the heater will kick on occasionally the other half. I have been using MERV4 fiberglass filters, replacing regularly. I found out about practical pleat filters (4-5″ deep filters that fit in the 1″ ceiling grilles) and was very interested. I have more than enough space in my filter boxes. Looking into them though, it seems like they did not stuff nearly as much filter area in them as they could have.

Practical Pleat:

r/HVAC - Filter area, pressure drop, etc

Filtrete MERV13

r/HVAC - Filter area, pressure drop, etc

With the number of pleats on the practical pleat vs the shown filtrete, it doesn’t appear that the practical pleat has even 2x the filter area at 5″ deep vs the Filtrete at 1″ deep, but the practical pleat is a lot more expensive.

Is this a fair comparison? Granted this is images online vs holding them in person, but I can’t find the practical pleat stocked locally. If both filters had the same MERV rating, I imagine that surface area is the main driver behind pressure drop. Both of these have a massive filter area compared to the fiberglass filter I am using, but are obviously much more restrictive per square inch…because they are actually filtering.

I am thinking at this point I will have to buy or build a manometer and measure the pressure drop across the fiberglass filter, and just ensure that whatever I buy is the same or better, but I am looking for pointers here.

Alternatively…am I barking up the wrong tree here? Should I just stick with cheap HVAC filters and rely on the air purifier alone for filtering allergens?