I just moved into a new house with a Trane Air handler (model TWE065E13FB) in the crawlsapce. I went to replace the filter as this was suggested maintenance and I found that there isn't a filter in the slot. Should I install a filter? If so what kind of filter? Looking online it seems that a 20x25x1 filter is the correct size.
The manual for the unit indicates the filter surface area (sq.ft.) should equal to CFM/300 for low flow and CFM/500 for high flow. I have 1600 CFM with a 4 ton heat pump (400 CFM/ton). If I use the high flow this gives 3.2 sq.ft., about a 20x25" filter. Is this the correct way to do this calculation. I can't see the filter slot accepting different sizes of filters without modification.
I'm not particularly sensitive to dust or allergens and on my return air vents I just use the basic Rheem/home depot pleated filter (20x20x1). Would a similiar filter be suitable for the air handler?