Work on the Concord, Mass., barn conversion focuses on a utility trench that must be built. Meanwhile, host Kevin O'Connor meets the couple who will live in the converted barn. Meanwhile, plumbing-heating expert Richard Trethewey checks out the heating and air conditioning at the New Yankee Workshop (he's thinking of a similar plan for the barn). On “Ask This Old House,” projects include fixing holes in drywall and replacing a toilet. Also: O'Connor, Trethewey, contractor Tom Silva and landscaper Roger Cook guess the uses of unfamiliar objects.