Borehole cost and jobsite disruption are the two things that usually kill ground-source heat pump scope on an urban retrofit. A Boston startup has just finished its first commercial job attacking both, and it did it under the headquarters of one of the largest GCs in the country.
Dig Energy drilled seven geothermal boreholes at Suffolk Construction’s Boston headquarters. The rig takes up about one parking space.
How the drilling method works
A high-pressure nozzle sprays water at 10,000 psi to cut the hole. The nozzle is consumed on each hole. The drill string stays in the ground and becomes the heat exchanger itself, which removes the separate loop installation step that conventional geothermal requires.
On the Boston job the company reports one-tenth the water use of conventional drilling and 75 percent less spoil hauled off site. It claims up to an 80 percent reduction in drilling cost. Dig raised a $5 million round around September 2025 and was selected for Boost, the accelerator run by Suffolk Technologies. It says it’s booked through mid-summer 2027 and has a next-generation rig in development.
Take the numbers as vendor claims
Every performance figure above is self-reported by Dig Energy CEO Dulcie Madden, with no third-party verification. Both companies explicitly declined to share specific cost numbers, so “up to 80 percent” is marketing rather than a unit rate anyone can bid against.
There’s a second disclosure worth stating plainly. Suffolk Technologies is an investor in Dig through its accelerator and Suffolk is the building owner, so partner Parker Mundt is not an independent voice on how well it worked. The roughly 1 percent US building geothermal penetration figure is also the CEO’s estimate.
Why mechanical subs should still care
Geothermal installs currently run up to five times the cost of an equivalent air-source heat pump, and most of that delta is the drilling. If a low-noise, parking-space-sized rig holds up even partially on cost, ground-source moves from a premium alternate toward something that can sit in a base bid on a commercial fit-out. Tight urban sites where a conventional rig simply doesn’t fit are the obvious first market.
The comparison point is what a full geoexchange plant looks like when it’s designed in from the start rather than retrofitted: the new Manning Institute of Biotechnology at the University of Virginia is served by an all-electric central plant with no combustion at all, running geoexchange with heat-recovery chillers and thermal storage. That is the easy case. Seven holes under an occupied downtown office building is the hard one, and it’s the one that has to get cheap.
Source: Canary Media.