Reducing cold infiltration from AC registers

D107

AC system is in attic, covers 6 rooms 1st and 2nd floor. We're working on dining room ceiling and now that the register is temporarily off--see photo-- I'm noticing alot of cold air blowing down from cold attic.

Of course with register on it's probably less but damper has been open year round. I thought perhaps a chimney effect was happening, with heated air rising up into 2d floor return register, then coming down through ducts. But I checked and there didn't seem to be much air flowing into the register, though it's much larger than a single duct so perhaps that wouldn't be as noticeable.

I suppose the easy answer might be to lightly mark the register's damper setting for summer use, and then close all the dampers--both at individual registers and at the manifold in the attic--every winter. And maybe also the return register as well.

I'm shocked I never thought of this before, but seems like quite substantial infiltration.

Thanks,

David

albandjann1725849

plug it

Put some loose fiberglass insulation in a plastic grocery bag to get it to hold shape. Stuff it into the space, leaving the handles exposed. Spray in some expanding foam insulation. You now have a formed, removable plug. Don't forget to remove when you turn on the A/C.