SumZero Energy Systems

SumZero Energy Systems has built a very large public record for a Holliston company — a 4.9-star Google average across 501 ratings, and 378 written accounts stretching from 2019 to today. Almost all of it is about one thing: heat pumps, and the Mass Save paperwork that comes with them. That rebate handling is the most consistent thread. A July 2026 customer who had seven mini-splits installed said the team helped obtain the rebates and walked them through the Mass Save heat loan. An April 2026 customer described a five-zone system where the company took care of the Mass Save rebate automatically and guided them through the zero-interest heat loan. A Reddit commenter in January 2026 reported a 2,000-square-foot townhouse job at about $17,000, down to $13,000 after rebates. The work also runs beyond heating and cooling: reviewers describe water heaters and old plumbing cleaned up, a Tesla wall charger with a new breaker box, and electrical service upgrades done alongside the mini-splits. Crews get named constantly and warmly — Paul, Matt, Dan, Raphael, George, Wyatt — and the recurring praise is punctuality, explaining the system, and cleaning up. Its Massachusetts HVAC licence, number 901-SM-B, is active, and the Better Business Bureau has accredited the company since August 2019 and grades it A+. The complaints are worth reading before you sign, because they cluster after the sale rather than during it. In an April 2026 review a customer wrote that an AC installation was shoddy and that support years later was close to none, describing several installers but only one or two service techs. In February 2026 another customer's heat pump failed during the coldest stretch of winter and was still unfixed a week later while a part came from Texas. A June 2026 reviewer gave Paul full marks but noted the visit was needed because an outlet SumZero had installed failed, the sump pump did not run, and water overflowed onto the basement floor. In March 2026 a homeowner with seventy-five-year-old asbestos-taped ducts found the company is not on the Commonwealth's list of approved asbestos contractors. And a June 2026 customer felt a $250 condenser cleaning should have been covered by the $100 annual Comfort Club fee. The pattern across those is not workmanship on install day — it is what happens when something goes wrong afterwards, and how much of the maintenance plan is actually included. For a Massachusetts homeowner converting off oil or gas to a heat pump, this is one of the more experienced and better-reviewed options around, and the rebate help is real. Ask specifically about service response times and warranty callbacks, what the membership plan does and does not cover, and — if your ducts are old — whether asbestos work is in scope.