If you put 2 6 inch heat ducts in a 16 x 16 foot room, how big of a cold air return would I need?

You have 54 square inches plus of supply and need about the same or slightly less for the return ."

What is the minimal a/c air return intake for a 4 ton? 16 sears?

What is the minimal a/c air return intake for a 4 ton? 16 sears?

There are 400 cfm per ton of cooling 4tn times 400 is 1600cfm so your duct can be 35 by 10 or 26 by 12 or the best choice 18 by 16 cause you can get snap together duct that size your return grill should be two of them instead of one big one sizes would depend on where they were placed. On that return duct you can also use 18" round pipe or if pulling it from two areas u can use an 8" and a 10" round pipes.

there are 400 cfm per ton of cooling 4tn times 400 is 1600cfm so ur duct can be 35 by 10 or 26 by 12 or the best choice 18 by 16 cause u can get snap together duct that size ur return grill should be two of them instead of one big one sizes would depend on where they were placed. on that return duct u can also use 18" round pipe or if pulling it from two areas u can use an 8" and a 10" round pipes.

There is NO relationship between CFM and BTU 'S. 1 ton of AC is 12,000 BTU. How you distribute the air is another story.