Combining Cold Air Returns

I need some opinions on a home renovation issue I have.
We are renovating our kitchen and this involved removing a wall. When I took down the wall I found not just 1 but 2 cold air returns running from the second floor above to the basement below. My original idea was to build a single column to contain the cold air return. Now that I have discovered that there are actually 2, not 1 I am wondering if it is OK to combine them into a single column. My idea is to build a bulkhead to join them at the ceiling and then either have both of them run into the same place on the floor, or to build a second bulkhead at the floor to allow each to return to it's original location.
Any thoughts on the best approach?
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It will work if the single is large enough to accommodate the air flow from both.
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Edwin Pawlowski wrote:

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