Thanks. The grille was in plastic with a 20x20 sticker on it, which means
nothing as it had a filter already crammed in it (19 1/8 square, and bent).
It's a pretty good company, so I don't know what's going on. The city is coming
out to inspect the air handler this week, so I'll let drop that I may chat about
this issue with her.
The plenum box measures 20x20 exactly, so it may be a close fit but the grille
is square.
They will have some fun as I'm asking my father (a mech PE) to run some numbers
Tuesday to see if the grille is sized correctly for the tonnage. I need to get
flow numbers from 3M, but I bet all the plenums are under size. The previous
owner of the house was a do-it-yourselfer, and now I'm cleaning up after him :-)

In article , TURTLE says...
This is Turtle.

There is something really wrong here with a 20 X 20 return air grill not taking
a 19.75'' x 19.75'' filter. all American manufactors of return air filter grill
make the filter area of a 20 x 20 return air filter grills , filter area will
be atleast 19 7/8" X 19 7/8" . they don't make them 19.5 " X 19.5'' at all. One
of two things here happen.

1] The contractor got stuck with some special order return air filter grill
that he ordered sized at 19.5" X 19.5 " and ring to pawn these odd ball filter
grills on you. Or the warehouse is Pawning them on him and he not know it at
all. In the HVAC business we have to order any different sizes of filter grills
for odd ball jobs and i have ordered 19.5" X 19.5" filter grill and can order
special order 19.5" X 19.5" filters to go in them.

2] The wall has shifted and mashed the filter grill to a point of it getting
smaller one way and it will be short one way and not the other. Measure both
ways and see. the filter grill can be crushed into a hole to a point of mashing
the filter grill to a smaller size.

if the hole where the filter goes masures 19.5" X 19.5" --- It is NOT a 20'' X
20'' filter grill like it was suppose to be. if you can't put real easy a
19.75" X 19.75" Filter in a 20'' x 20'' return air filter grill. you need to
bring the filter grill back to get the correct size that goes in it.

In Over 40 something years in the HVAC/R business I have never seen one
installed correctly, not a odd ball size filter grill to start with , that the
filter would not fit fine in the filter grill.

Something is just too fishy here ! Call the hvac contractor back and clear this
mater up.

TURTLE