Thanks for the replies. The floor is hardwood and there is almost an inch of space btw the door and the floor. I already have the 8 inch line so that's why I was going with the 8. The space alone under the door doesn't seem to be enough. The ceilings are 12 feet and it does stay noticeably warmer and dryer in there which I really don't have a problem with but the wife thinks it's not good for the food and leaves the door open which makes me crazy. I thought this might be the easiest thing but I wasn't sure if the ducting was rated for the negative pressure or if there could be a downside to trying this and if it would be effective? The pantry is only about 15 feet from the unit in the attic and about 30 feet away from the ceiling intake where the filter is located for this unit. To me it does not seem like it would make any difference in the conditioning of the air in that section of the house if I drew some of the air through a 12 inch filter grill in the pantry ceiling but again, I just wanted to check with someone in the know first. If I use a regular 8x6 register than I would be sending unfiltered air through the unit and that doesn't seem like that would be wise would it? (The filter is located in the ceiling for the return air and I was going to attach the new 8 inch line to the unit in the attic.) Thanks again for the helpful replies.

no. unfortunately that doesn't answer my question. i already have aftermarket grilles that i like. the problem is that the cold air return grille is not hinged, making replacing the filter difficult. i'm looking for a way to modify it to make this easier. completely different issue. additionally the ones we found that we like were from a company called Reggio: Here is a link that might be useful: Reggio

If a new grill has the same exterior dimensions, won't the old holes will be covered if the new one's screw holes are in different locations? These things are usually screwed in with small diameter self-tapping screws that are easy to screw in so it really isn't necessary to hit the old holes or to make new guide holes first. Or do you have a different concern in mind?

I believe building codes don't allow returns in kitchens, for many reasons. I'd completely disconnect that one and put another elsewhere in the house. Wall cavity returns are passe, not a good idea, also for a variety of reasons. Is there no way to run return ducts to grills in ceilings, walls, or (last choice) floors? As far as needed size of return flow, this is a function of the draw of the furnace fan (size of unit determines air flow) and the supply ducting. This is something any HVAC contractor can calculate.