I removed the unit below the dash to get my heater matrix recored (one of the first jobs I did when I first got my Flavia in 2009). The hardest part of the job is wiggling the heater matrix inlet / outlet pipes down through the bulkhead, as there isn't a lot of clearance.
I replaced the fan with one that is designed for cooling a PC. It generates good flow and runs quietly, but in retrospect, I think I should have blanked the gaps around the edges. It was easy to do and a simple mod. I also added a secondary fan in the vertical pipe that ducts air up to the windscreen and fascia side vents.
In saying all of that, I seldom find the need to use the fan unless I'm in slow traffic. The ducting from engine bay generates more air flow than the fan does when you're on the move.
