Richard Trethewey is an American plumbing and heating expert and television personality best known for his longtime work on This Old House and Ask This Old House. A licensed master plumber, he joined This Old House in 1979 and has since become one of the program’s most enduring experts, explaining plumbing, heating, cooling, and mechanical systems to homeowners. Trethewey is also a principal of RST Inc., a manufacturers’ representative company serving the plumbing and heating industry.