I have a trane heat pump in my attic, do I replace the filter in the air handler AND return grill? Not sure if I can use just the return grill which is in my hallway ceiling


If you have 2 filters racks in your system you could just pick the easiest one to change and ues it exclusively. You could also use both and change the second one less often. That seems like a lot of monitoring. You may have to check both often at first until you are able to determine a schedule. It's not a bad idea but in most cases that level of filtration isn't required.

  • If you just change the return air grille filter, then you’d miss the OSA, right?
    – Lee Sam
    Apr 6 '19 at 5:45
  • I just use the filter that's in the air handler in the attic. The return registers (2 of them, actually) have no filters.
    – SteveSh
    Jan 1 '20 at 21:50

Filtering the return air at the point of ingress is by far the best option. That way there is no dirt accumulating in the return ducts and you can readily see the condition of the filter.

I removed my internal filter and put in a surface mount 20x20 Merv13 on top of the former return grill which I also removed. It's a vertical configuration and it's protected from anything falling on it, kicking it, etc. The grill just reduced the air flow and was a dirt magnet itself.

  • The problem with dispensing with the filter in the air handler is that the air return ductwork between the filter(s) will be at reduced pressure and can leak unfiltered air into the air handler. With the filter in place in the air handler, air is filtered just before the air is forced through the furnace and the a/c coil. The air handler just after the filter is then the only volume at the lowest pressure. This volume is presumably tightly sealed by the factory and should be leak free. Dec 22 '20 at 13:50
  • That's a good point. You have to trust your duct. In my case it's mounted directly on the side of the unit.
    – lordadmira
    Dec 22 '20 at 16:11

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