A Net Zero Home on Martha’s Vineyard

Matt Millard of Performance Mechanical heated a 1,500 sq ft addition on his own Edgartown home with Ecowarm RadiantBoard EPS and an air-to-water heat pump. Through a New England winter, the backup elements never fired.

LocationEdgartown, Massachusetts

Size1,500 sq ft addition

ContractorPerformance Mechanical Inc.

Matt Millard, owner of Performance Mechanical Inc., at his home in Edgartown, Massachusetts

A contractor who likes to experiment

Matt Millard owns Performance Mechanical in Edgartown, Massachusetts. His career has spanned commercial piping, mechanical work and residential heating, and he installs plenty of efficient air-to-air heat pumps. For his own home addition he wanted to step up to hydronic radiant heating driven by an air-to-water heat pump.

He added a 1,500 sq ft multi-purpose room plus a bedroom and bathroom over his attached garage workshop, with 14-foot ceilings and large windows in the great room. It is one part of a wider strategy to bring the house to Net Zero Energy.

Why the panel choice mattered

Ecowarm RadiantBoard is a low-mass, fast-responding panel system designed to run at lower supply water temperatures, which lowers operating cost and makes the room quick to heat up and cool down.

The mechanical: air-to-water heat pumps

The piping is as simple as it gets. Warm water runs from the outdoor monoblock air-to-water heat pump into the silver buffer tank, and from there to the radiant floor above through a variable-speed pump and PEX manifold.

“That’s why I wanted to try out the Chiltrix air-to-water heat pump matched with Ecowarm RadiantBoard. The Chiltrix is a monoblock design that keeps the pre-charged refrigerant outside. I think my future may easily be installing hydronic systems indoors with the condenser refrigerants staying outdoors.”Matt Millard

For anyone tracking heat pump performance, the low supply water temperature is the whole point: it raises heat pump capacity at the low ambient temperatures New England delivers.

Why radiant is the right choice for net zero

90–120°FLow supply temp, ideal for heat pump pairing

3.0–4.5Heat pump COP at 120°F supply

Up to 30%Annual fuel savings vs. forced air

25–50 yearsSystem lifespan, fewer replacements needed

Source: WBI hydronic specs and heat pump performance data at low supply temperatures.

Radiant also suits the room itself. It heats a large-volume space better than forced air, so Millard avoided ceiling fans pushing hot air back down from the 14-foot ceilings.

“The integrated EPS radiant panel spared me the time and expense of insulating under the subfloor.”

CLIFF MEEHAN · LONG AND MEEHAN BUILDERS

Installation: paint by number

Ecowarm RadiantBoard staff provided a complete CAD layout covering panel locations, panel count, PEX requirements and manifold positions. Millard is a plumbing and mechanical contractor by trade, so he had Cliff Meehan of Long and Meehan Builders, also of Edgartown, install the insulated EPS panels on the addition subfloor to stop heat escaping into the workshop below.

Ecowarm RadiantBoard EPS is available in a 1 1/8-inch R-2.70 panel, but this project used the thicker R-5.6 because the space below is unconditioned.

Radiant heat in floors, walls and ceilings

The same system stretches beyond the floor. Different models let installers build a radiant subfloor, a radiant wall or a radiant ceiling — on this project it went into the shower and a sunken bathroom as well as under hardwood.

“It’s now just part of my radiant problem-solving toolbox. We largely do major remodels of big, custom homes that present challenges we can meet.”Cliff Meehan

Carbon output by system (lbs CO₂/yr)

0 lbsHeat pump + radiant

3,500–4,500 lbsGas radiant

5,000–6,500 lbsGas forced air

Source: EPA emission factors, 2024.

Watch the floor come up to temperature

The results

Through the past winter the 1,500 sq ft addition was heated entirely by the 2.5-ton Chiltrix air-to-water heat pump, without ever calling on the backup electric elements in the buffer tank. Installation was clean and dry, with none of the mess of the cement pours Millard had used previously.

A version of this project was featured in Plumbing & Mechanical Engineer Magazine. Written by Morgan Muir, a hydronic manufacturers representative and product developer in the radiant industry since 1988.