Clog-free gutters are installed at the Carlisle, Mass., farmstead. Inside: cherry flooring, rails for the barn stairway, cabinets and a wine cellar. Meanwhile, plumbing-heating expert Richard Trethewey tours an industry design-and-testing facility. On “Ask This Old House”: leveling a Massachusetts homeowner's uneven concrete floor to facilitate the installation of hardwood flooring; repairing a Georgia homeowner's leaky water-shutoff valve. Also: a primer on air compressors.