This question is about a forced air HVAC unit. (Central Air with the heater portion being natural gas). It is in a new 2400sq' house, installed in an insulated 4' high crawl space. It has three return ducts coming off a central return line in the middle of the house. The first floor is 12”x 24” located in the living room just below the thermostat. The second floor has one 12”x12” in the master bedroom mounted low on the wall as you come in. The third vent is 16”x16” just outside the bedroom in the upstairs hallway mounted at eye level.
They all had those cheap blue filters and seemed to work fine (noise, airflow, etc). I was told they should be replaced with the better corrugated paper filters with more surface area that filter more. I did that and soon I noticed that it was pretty noisy, but tolerable when operating. After doing some research I read that it would be better to have more and bigger return ducts. When it was time to replace the filters, I noticed that the cutout in the actual ductwork where the filter box mounts to the main return duct was about half the size of the filters. Bigger is better right? I then took a sawsall and enlarged the actual opening to almost double what it was, to almost the size of the corresponding filters. I thought by doing so everything would breath better and the fan motor would be less stressed. Big mistake? The noise is now intolerable, and the better filters are being distorted and sucked inward. I tried running without any filters and things are whisper quiet although very drafty near the return ducts due to the air moving so fast. I then tried putting the cheap blue filters on to slow the air flow and that seemed to help a lot as far as noise and airflow.
My question is , are there better air filters with very low resistance out there? Or should I be satisfied with the practically useless ones that I have back on. Can I have one of those statically charged filters installed down in the crawl space and do away with filters up in the main house? Should I close up the openings back to the original size? I assume the airflow rates were checked and balanced when the HVAC was installed in the first place , but I have very little faith in the builder at this point because of other major problems.
Thanks for any insights in advance,