We added a 12X28 1st floor addition to the house (replacing an old 10X10 addition) over a crawlspace and 6X10 mudroom that is on a slab connecting the garage and the new addition.

The addition is being used as a kitchen and family room, has an 8' ceiling and is presently being fed by 2 - 8" flex supply ducts running through the crawlspace. The addition is open to the rest of the house by 2 -48" doorways. There are no returns in the addition.

This room typically runs 2-3 degrees cooler than the rest of house and is more sensitive to extreme cold temps outside than the rest of house. It is fully insulated and has been inspected.

The house has a forced hot air system and also central air for cooling.

We are exploring options with our contractor for addressing the temp variation and also to bring heat into the mudroom.

Would a floor return duct, placed in the family room side of the addition help to even out the temps with the rest of house?

Also, outside of adding a small electric heater in the mudroom, which I am reluctant to do given the high cost for electricity here, would a small supply duct, fed by a 4" round work?

Another option we discussed was a passive register located just under below the ceiling on the wall connecting the mudroom to original house to bring some warm air into it.

Are there any other options available to us?