Ask This Old House plumbing and heating expert Richard Trethewey shows an efficient, low-maintenance way to humidify the air. (See steps below.) SUBSCRIBE to This Old House: http://bit.ly/SubscribeThisOldHouse Richard visits Charlotte, NC to install a whole-house humidifier. A whole-house humidifier should be installed by a professional HVAC contractor. Steps for How to Install a Whole-House…