I live in a 830 sq ft bungalo home we have a newer furnace . But our old furnace required a large 16x24 cold air return in our hallway . My question is can I make the return smaller and how small can I go? Thank you

Making the return small will restrict the air flow, probably raise return air noise, possibly overheat the exchanger and can cause the heater to shut down. For proper air flow, the return opening area should be very close to the supply area. What is your issue? With a basement or crawl space you should be able to add return and THEN reduce the larger single one.

Have A Cold Air In the basement and Alls I Really want to do is Make the one I Have in hallway just to standard size would that be okay? And thank You For taking the time For This

Depends on what you consider "standard" size. There are any number of sizes and thicknesses. 20 X 24 X1 is fairly common, 24 X 24, 24 X 36 etc. It also depends on what MERV rating you want. What size do you have now?