Evan Trethewey is the president of RST Thermal, a New England manufacturer’s representative firm that supplies and teaches heating, ventilation, and cooling technology to the people who actually install it. If the last name sounds familiar, that is because it has been showing up on public television screens since 1979. His father, Richard Trethewey, has been the plumbing and heating expert on This Old House for more than four decades, and his grandfather Ron Trethewey held the role during the show’s very first season. Evan, though, has built his working life mostly off camera, running the business side of a family trade that stretches back well over a century.
That distinction matters. A lot of people who search his name expect to find another television personality. What they find instead is a fairly quiet operator who took a small rep agency his father started in the late 1980s and helped grow it into something with a physical home, a teaching mission, and a reputation among contractors across the region. This article walks through what is actually known about his career, the Fall River facility he helped build, and why his corner of the trade is more interesting than it first sounds.
Who Is Evan Trethewey?
Evan Trethewey serves as president of RST Thermal, the manufacturer’s representative company founded by his father, Richard Trethewey. This Old House confirms the role directly on its cast page for Richard, noting that both of his sons work in the industry and that Evan holds the top job at RST. It is a straightforward fact, but it is one of the few things about him that is documented in a primary source rather than scraped from a business directory.
Professionally, he carries the CPMR designation, which stands for Certified Professional Manufacturers’ Representative. That credential is not decorative in this line of work. It comes out of a multi-year program aimed at people who run rep agencies, and it signals that someone has been trained in the commercial side of representing multiple manufacturers at once: territory management, contracts, forecasting, and the ethics of standing between a factory and a contractor. He lists it publicly alongside his name, which tells you something about how seriously he takes the business discipline of the job rather than just the product knowledge.
Business databases such as Crunchbase list him as a Fairfield University graduate who worked in sales and marketing at Cape Cod Fire Logs before moving into his current role. Those entries are typically pulled from LinkedIn rather than reported independently, so it is worth treating them as reasonable but unconfirmed background rather than hard biography. What is not in dispute is where he ended up and what he does there, and honestly, that is the part that matters to anyone in the trade.
A Family Trade That Goes Back to 1902
To understand Evan Trethewey’s career, you have to start about a hundred and twenty years before it. According to This Old House, Richard Trethewey’s great-grandfather and his brother founded Trethewey Brothers in Roslindale, Massachusetts, in 1902. That makes Richard the fourth generation in the trade, and it makes Evan the fifth. Very few American family businesses survive that long in any industry, let alone one as physically demanding and economically cyclical as plumbing and heating.
The television connection came almost by accident. Russell Morash, the creator of This Old House, called Ron Trethewey in 1978 because Trethewey Brothers had a strong local reputation. Ron took the on-camera role for the first season, discovered he enjoyed the show far more than he enjoyed the cameras, and handed it to his son Richard in 1980. Richard has been there ever since, and the family name became shorthand for competent, patient explanations of hydronics and heating systems.
Evan grew up inside all of that, which is a specific kind of upbringing. When the family business is the trade and the family trade is also a national television segment, you absorb both the technical vocabulary and the public-facing responsibility early. His brother Ross took the engineering route, earned a professional engineer license, became president of TE2 Engineering, and now appears regularly on Ask This Old House as the building and renewable energy expert. Evan took the commercial and distribution route. Between the two of them, they cover most of the ground their father covers alone on screen.
Building the RST Thermal Training Center in Fall River
The most visible project of Evan Trethewey’s career so far is the Fall River facility. This Old House documented it in a segment where host Kevin O’Connor toured the building with Richard, and the network describes it plainly: Richard and his son Evan spent roughly a year renovating a former mill building, originally constructed in 1904, into a state-of-the-art educational and showroom facility. The segment aired as part of Ask This Old House season 22 in April 2024.
The building itself is a good story. Fall River is an old industrial city on the Massachusetts South Coast, full of enormous granite mill structures that once ran textiles and have spent decades looking for a second life. Converting one into classrooms, working system displays, and showroom space is not a cosmetic renovation. Mechanical equipment needs real infrastructure, real venting, real electrical service, and enough floor area that a contractor can walk around a boiler or a heat pump and see how it is piped rather than looking at a cutaway in a brochure.
The purpose behind it is where Evan’s thinking shows. RST could have kept operating out of an office with a catalog and a truck, the way plenty of rep firms do. Instead the facility was designed so that contractors, builders, architects, engineers, and homeowners can see systems actually running. This Old House notes that the goal is to demystify the mechanical world and give people enough understanding to make better decisions, and that RST frames this as lifting the whole industry rather than just its own sales. In a trade with a widely discussed labor shortage and a wave of new heat pump and hydronic technology arriving faster than most crews can learn it, a permanent teaching space is a genuinely useful contribution.
What a Manufacturer’s Representative Actually Does
This part trips up a lot of readers, so it is worth spelling out. A manufacturer’s rep firm does not manufacture equipment and does not install it. It sits in between. RST Thermal represents a set of heating and cooling manufacturers across a defined territory, in this case New England, and acts as the local face of those brands for wholesalers, contractors, and specifying engineers.
The work is part sales and part technical support. When a boiler manufacturer in Europe wants its condensing product line specified in a Massachusetts retrofit, someone has to explain the controls to the installer, help the engineer size it, troubleshoot the first few jobs, and stay reachable when something behaves oddly at two in the afternoon on the coldest day of the year. That someone is the rep. RST’s own materials describe the company as being built around quality hydronic heating and cooling products backed by technical support and customer service, which is the standard promise, but the training center is the part that makes it more than a promise.
Running that kind of firm is a management job more than a wrench job. You are balancing several manufacturers who all want more of your attention, a contractor base that trusts individuals rather than logos, and a product category that has been changing quickly as electrification and efficiency standards reshape what gets installed. Doing it while carrying a last name that already means something in the region adds an interesting kind of pressure. The name opens the door, but it does not close the sale.
His Public Profile and What He Is Not
It is worth being clear about one thing, because plenty of online summaries get it wrong. Evan Trethewey is not a cast member of This Old House or Ask This Old House. His brother Ross has hundreds of on-air credits as an expert. Evan appears as a subject when the show covers the family business, most notably in the showroom tour, but he is not an on-screen host or specialist.
He does turn up in trade media, which is a different and arguably more relevant venue. Industry podcasts and HVAC publications have featured conversations involving the Trethewey family about hydronics, heat pumps, and training, and regional trade associations have highlighted RST and its leadership. That is the audience he is actually speaking to. Contractors do not need another television segment; they need someone who can explain why a particular buffer tank arrangement keeps short-cycling their new system.
Beyond his professional life, there is very little verified public information about him, and that appears to be intentional. Sites that promise details about his personal life, net worth, or family are almost always recycling guesses. A responsible profile stops where the record stops, and in his case the record is his company, his credential, and the building he helped create.
Conclusion
Evan Trethewey occupies an unusual spot: fifth generation in a trade family, son of one of the most recognizable figures in American home improvement television, and yet mostly known within his own industry rather than outside it. He runs RST Thermal, he helped turn a 1904 Fall River mill into a working HVAC training center, and he carries a professional credential that reflects the commercial side of the business rather than the celebrity side.
For homeowners, the takeaway is indirect but real. The quality of a heating system installation depends heavily on whether the contractor doing the work understands the equipment, and that understanding usually comes from somebody upstream who bothered to teach it. That is the job Evan Trethewey has chosen. It is less visible than a television segment, and over the long run it probably matters just as much.
Also read: Roger Cook Net Worth: Career, Business, Life, and Legacy
FAQs
Who is Evan Trethewey?
Evan Trethewey is the president of RST Thermal, a New England manufacturer’s representative firm for heating and cooling equipment. He is the son of This Old House plumbing and heating expert Richard Trethewey.
Is Evan Trethewey on This Old House?
No, he is not a cast member or on-air expert on the show. He has appeared as a subject in a segment about the family’s RST Thermal showroom, but his brother Ross is the one with a regular on-air role.
What is RST Thermal?
RST Thermal is a manufacturer’s representative company founded by Richard Trethewey in the late 1980s that supplies and supports hydronic heating and cooling products across New England. Evan Trethewey now serves as its president.
Where is the RST Thermal training center located?
It occupies a renovated 1904 mill building in Fall River, Massachusetts. Richard and Evan Trethewey spent about a year converting it into a showroom and educational facility with working system displays.
How is Evan Trethewey related to Ross Trethewey?
Ross Trethewey is his brother. Ross is a professional engineer, serves as president of TE2 Engineering, and appears regularly on Ask This Old House.
