Does this filter rack work with the GV96VTN 21” model in downflow mode.

Yes, the FR1625-1 can be used with a 21-inch GV96VTN in downflow mode as long as it is installed in the bottom return-air duct and the ductwork is sized appropriately for a 16" × 25" filter.

If you have any further questions, please call us and we will be happy to assist you.