SumZero Energy Systems

SumZero is a Holliston shop built around heat pumps and electrification — mini-splits, oil and gas conversions, panel upgrades, EV chargers — and it's grown into one of the busier HVAC crews in the area, with 501 Google ratings averaging 4.9. The company says it started with two people meeting in a Florida training room and at a Panera Bread table, and has since done more than 1,800 installs across Massachusetts, though it gives no founding year. Its Massachusetts HVAC license is active on the state registry, and it carries an A+ rating from the Better Business Bureau. It's kept up that pace recently too — 67 reviews came in over the last six months alone. Reviewers name a rotating cast of technicians — Raphael, Matt, Paul, Gabriel, Dan, and others — and consistently describe them as prompt, thorough, and easy to reach with questions. Recent reviews describe full mini-split installs completed within about a week of signing a contract, a five-zone system with a dedicated electrician on the crew, and use of Mass Save's heat loan program with SumZero handling the rebate paperwork. One reviewer, a customer since 2022 when SumZero installed a whole-home Fujitsu heat pump system, says a technician walked them through the shop on top of finishing the install in seven business days. The company also runs a maintenance membership, its Comfort Club, that brings technicians back for annual mini-split and condenser inspections. A handful of reviews describe real problems. In June, one reviewer said an electrical outlet SumZero had installed failed and caused a sump pump to stop running, flooding part of a basement — though the technician who came out to fix it separately got five-star marks for how he handled it. An April review described a shoddy air conditioning installation with weak follow-up support years later and turnover among installers, and a March review said a request to replace old asbestos-taped ductwork never turned into a workable quote. In a February 2026 review, a customer's heat pump failed during a cold snap and stayed out for a week, and a 2025 Angi review said three installed systems all malfunctioned within their first year, with the company going unresponsive afterward. This is a strong call for a heat pump, mini-split, or electrification project, especially if you plan to use the Mass Save rebate programs — the company's size means a large crew and fast scheduling. Ask specifically who handles service calls if something needs fixing after installation, since that's where a few reviewers ran into trouble.