To restate some info from my previous post, I live in southern New Mexico and I was interested in upgrading the air filtration of an old furnace with an external or internal air cleaner such as the Aprilaire 2210, 2410, or 2250.
I have an older PBKM-LD12N080C furnace manufactured circa 1994 that is installed in a small closet in the garage. This is an upflow furnace with a bottom return. Instead of having a conventional cold air return from the attic, indoor air is drawn into the blower from a central location in an adjacent room up through the wooden base/pedestal which supports the furnace.
The previous owner of the house haphazardly placed a 16x25x1 filtrete filter over top of the junction between the hole cut in the particle board base/pedestal and the blower compartment. The filter is actually too small to completely cover the opening and so an additional length of filter media was used to plug this area. Both are held down, loosely, in place by a piece of wood. I would've replaced this right away because the furnace manual actually recommends a 16x27x1 "high velocity" filter, but I've been unable to locate one.
As far as I can see, there is no proper filter rack inside or outside of the furnace. According to the furnace manual, an "internal mount bottom return filter accessory" 1BF0301-4 was available at one time, but I've had no luck finding these. I've even tried contacting the manufacturer for help with this, but I've received no response to my emails.
Because of this, I was considering an upgrade of the furnace's air filtration with the Aprilaire furnace air cleaners, though these, and similar cleaners, appear to be installed between the cold air return and the side of the furnace. This old furnace doesn't have cold air return ducting, so I'm not sure where to install an air cleaner.
BTW, there are two narrow, parallel ducts in the upper left corner of the furnace closet which connect to nothing either in the furnace closet or the attic. Any idea what this pair of slim ducts was intended for?
Once again, any help would be appreciated!