Richard S. Trethewey (born c. 1956 in Dedham, Massachusetts) is an American plumber and HVAC contractor, who is best known as a television personality, appearing regularly on This Old House and its spin-offs, Ask This Old House and Inside This Old House. In 1979, producer Russell Morash called on Trethewey Brothers to lend their expertise to his then new home improvement television series. Richard's father Ron filled the role for a season, and then turned the job over to his son, who has handled the duties ever since. Richard is a registered journeyman and master plumber in the Commonwealth of Massachusetts. For each This Old House project, he oversees all plumbing, heating and air conditioning renovations. For Ask This Old House, he offers his expertise to viewers who write in with questions related to plumbing and HVAC, and occasionally visits a viewer's home.
In 1990, he left Trethewey Brothers to form his own company, RST, Inc. RST is a manufacturer's representative for several lines of plumbing and HVAC equipment ranging from pipes to complete systems. Located in Westwood, Massachusetts, the company serves much of New England and employs nine people.
Recently Richard Trethewey's sons, who are in their father's business too, sometimes appear on This Old House.