My son suffers from very bad allergies. We currently have a 13 air filter and have had all the ducts cleaned, however we are also looking for air filters for the vents themselves for his room only. Downfall is when they installed this heating system about 20 years ago, they installed the vents in the ceilings of the second floor and they are the round commercial style.

Does anyone know of any round vent filters on the market?