An old cannonball, perhaps from the War of 1812, has been found on the grounds of the Carlisle, Mass., farmstead, where framing work progresses on the Greek Revival house and the new connecting ell. Meanwhile, two carpentry students join the team as apprentices, and host Kevin O'Connor visits Yale University's Building Project, where graduate architecture students “learn by doing.” On “Ask This Old House,” plumbing-heating expert Richard Trethewey replaces a hot-water heater's sacrificial anode rod and helps a homeowner cool off by installing thermostatic valves on her steam radiators, while contractor Tom Silva installs a “cricket,” or rain diverter, to draw water away from another homeowner's front steps.