Hi all -- this is my first posting to GardenWeb, but I've found "lurking" to be very useful over the years. Looking forward to getting some assistance if possible.

So, I have a cold-air intake vent in my living room floor for the forced-air furnace. For the past few years, I've only had a buffet table above it, giving plenty of air circulation. I'm now thinking of putting a larger piece of furniture in this corner, such as an armoire or hutch. I realize that I'll still need to leave air space above the floor intake, but I'm wondering how much. Would six inches be adequate, or would 4 inches do? Or should the bottom edge of the furniture be even higher? My furnace has always worked well, so I don't want to do anything that would compromise efficiency.

The floor vent is 26 inches by 18 inches, if that helps.

Thanks!
CK