Return opening sizing?

[68malibu383]

Hey guys,
I inspected a town house built in 1966 today that is about 1,000 sq ft and two stories. Has a 2 ton Trane gas package unit installed in 2009. What I question is the return size. The second floor does not have a return and the one downstairs has a large filter (20 x 25) but the return cavity is actually under the kitchen cabinets.

The opening to the underside of the cabinets is about 6" high and 18" wide. So, the air flows through the filter then down to the floor and under the bottom of the cabinets through the 6 x 18 opening. How is the opening size calculated and does this seem too small for the system/home?

[cartercrew]

Based on current ICC mechanical codes, that return is too small. Current requirement is for 6" of return for each 1000 BTU of cooling. 2 tons needs 144 square inches (24 X 6), you have 108 (6 X 18). The return you have is adequate for 1.5 ton. Because of the cabinet situation, I would probably look at adding a return to the second floor to make up the difference.

[beachtech]

is it not 216? or am i using the wrong formula?

[beenthere]

is it not 216? or am i using the wrong formula?

I think you did 3 tons instead of 2 tons.

1.5 tons=18,000. 18X6=108
2 tons=24,000. 24X6=144
2.5 tons=30,000. 30X6=180
3 tons =36,000. 36X6=216
3.5 tons=42,000. 42X6=252
4 tons=48,000. 48X6=288
5 tons =60,000. 60X6=360

[genduct]

for whatever value this Code rule of thumb has.

I think we are now talking GRILL size for the opening and that should be larger.
Agreed?

[beenthere]

How is the opening size calculated

He asked about the opening size.

[68malibu383]

The grill is huge and the actual return duct is large enough I think (can't really get to it but put my camera under the cabinet and took a pic). Between the two, there is a restriction by the 18 x 6 opening. I was concerned about the restriction.