Why are there two air filter slots in my HVAC system?

furnace filter slot cover   Dan furnace filter slot cover

Maintain your home HVAC with air filter accessories from Lowe's Most accessories are easy to use so you can make changes to your system quickly, without

filter each month in case heavy use caused your filter to clog up Step 3: Replace the filter by sliding a new, clean filter into the slot  Shop around on the internet for the filters, and buy them by the case You will Never put more than one filter in a filter slot I have overheard

splashtastic slot review I have a house where the furnace has a 25 x 1 wide slot in the air intake where I slide the 16x25x1 filter in from the top  Note that there is no door that closes to cover the filter slot It's permanently open by design AFAIK Thanks More Pictures Filter