Myself and many others have been running these 2x2 which is plenty for most home mycology needs . I know horizontal has been the preferred option but not sure why honestly.

https://www.amazon.com/HEPA-Filter-22-6x22-6-Cleanliness-Mycology-Mushroom/dp/B0936Q63G5/ref=mp_s_a_1_1_sspa?crid=2Q0YZCTHTYS6O&keywords=ffu&qid=1684728209&sprefix=ffu%2Caps%2C486&sr=8-1-spons&ufe=app_do%3Aamzn1.fos.2b70bf2b-6730-4ccf-ab97-eb60747b8daf&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUExMVRTSDlMRDFGR09JJmVuY3J5cHRlZElkPUEwOTEyODMxMjc1TDY4N1hXNDAwJmVuY3J5cHRlZEFkSWQ9QTA2MjA2ODVYTFo0MFU3RERMN0cmd2lkZ2V0TmFtZT1zcF9waG9uZV9zZWFyY2hfYXRmJmFjdGlvbj1jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ==