My experience with gas forced hot air heating systems in residential homes always found the filter located in the furnace, between the air return duct and the combustion chamber.
I just recently encountered systems where the filters (at least 3 per furnace) are located directly behind the return ducts in the room locations – one of which is 12’ off the ground, requiring a ladder to replace the filter. These systems are in relatively new houses, built 2006-2008, two story without basements, and the two furnaces (one for each floor) are located in a second floor utility room.
In return for the inconvenience of having to replace multiple filters in difficult to reach locations, is there an advantage to having multiple filters versus one per furnace? Does the location of the furnace above rather than below the heating space require filters at the returns?
Do the furnaces have traditional filters, too? Recently I’ve seen small filters that homeowners can purchase and install right inside the ducts (didn’t notice if they specified return or output, though) but I figured they were additional to the traditional filter and marketed to people serious about removing as much junk from their air as possible.
The house I’m in is recent construction, and the filters are all behind the return grilles on the ceiling. The one in the master bedroom is in the lower portion of a tray ceiling and can be reached with the help of a chair, but the others need ladders to reach. (There are two separate systems, and the upstairs system has two returns.)
The furnaces / air handlers are in the attic with no filters up there. Given the alternative, I’ll deal with needing a ladder, rather than having to go into the attic.
**In return for the inconvenience of having to replace multiple filters in difficult to reach locations, is there an advantage to having multiple filters versus one per furnace? **
As a practical matter, no.
I suppose that multiple filters in different branches of the main return trunk mean that you’ll have more media filter material, and therefore need to change thew filter less often. But thats not why you see it that way. A cheap, inexpensive duct installation involves one central return. Having multiple returns-----in different areas-----means you’re drawing return area from a broader area----which means better overall comfort.
Thats why you’re seeing multiple returns—its for better comfort.
Does the location of the furnace above rather than below the heating space require filters at the returns?
No. See above.
The placement of the furnace is really an issue of logistics----trying to make the best use of time and space. There may be some slight difference to comfort—but if a system is designed and installed correctly you’ll never notice----either in comfort or utility costs.
That said, running duct through unconditioned spaces----like attics and crawlspaces---- can raise your utility bill (and even effect comfort) if they’re improperly installed.
But…placement of returns is just about always done for convenience. (and that sometimes means the convenience of the installers, unfortunately)
Smart installers will spread the outlets and returns around the rooms to get you the best circulation for the electrical buck. Clearly they are also limited by space and access, but putting the filters at the return inlets will ideally eliminate having to vacuum out the ducts every few years, getting the bugs and lint and stuff that have stuck to the metal. Any installer that runs uninsulated ducting over or under the living space is an idiot.