I am building a custom shelving unit that will sit over an inconveniently located floor vent/diffuser. My thought is to raise the bottom shelf up on stubby legs so that it does not block the vent. The question is, how tall do these legs need to be to gain sufficient clearance?
The register itself is a standard 4" x 10" opening. It seems to me that the space I am creating under the shelf is functionally equivalent to if I were extending the vent with a 90 degree turn. By this logic, I believe I should only need 4" of vertical clearance under my shelf. As long as I do not create a bottleneck that is any smaller than the cross-sectional area of the vent itself, it should be fine, right?
Is this reasoning correct? I've read various recommendations, some saying that I need as much as 18" clearance. This seems like ridiculous overkill to me.