Air-to-Water Heat Pumps: The Technology That Could Replace Your Boiler

Published by Sundial

Most of the heat pump conversation in recent years has been about mini splits — and for good reason. But there’s another category of heat pump technology that doesn’t get nearly as much attention, and it may be an even better fit for a large number of New England homes.

Air-to-water heat pumps are quietly becoming one of the most compelling heating solutions available. If your home has radiant floor heating, hot water baseboard, or cast iron radiators — and you’ve been wondering how to get off oil or gas without ripping everything out — this is worth understanding.

What Is an Air-to-Water Heat Pump?

Most people are familiar with the concept of a standard heat pump: it moves heat from the outdoor air into your home rather than generating heat by burning fuel. That’s the same principle at work here — but instead of heating air directly, an air-to-water system transfers that heat into water.

That heated water then circulates through your existing hydronic system — your radiant floors, baseboards, or radiators — just like a boiler would. From the perspective of your heating distribution system, nothing changes. The floors are still warm, the radiators still work, the domestic hot water is still there. What changes is what’s producing the heat. Instead of an oil or gas boiler, you have a refrigerant-based system pulling free energy from the outdoor air.

It’s the cleanest replacement path for hydronic homes, and for New England — where oil-fired boilers are still remarkably common — that matters enormously.

Why Air-to-Water Makes Sense in New England

New England has a specific problem that air-to-water heat pumps solve unusually well.

A huge portion of the housing stock here was built before forced-air systems were common. Old colonials, capes, Victorians, triple-deckers — these homes were built around radiators and hot water baseboards. They heat beautifully with hydronic systems. And for decades, the only realistic way to heat them was a boiler burning oil, gas, or propane.

That’s meant New England homeowners have faced a frustrating choice: keep paying for heating fuel with no good electric alternative, or do a whole-home renovation to add ductwork for a forced-air heat pump. Neither option is great.

Air-to-water heat pumps change that equation. They slot into the existing hydronic system without requiring new distribution infrastructure. The radiators stay. The radiant floors stay. The plumbing stays. You remove the boiler and connect the heat pump in its place.

Beyond the retrofit story, there are a few other reasons this technology fits New England well:

Cold-climate performance has caught up. Earlier generations of air-to-water heat pumps struggled in sub-freezing temperatures, which made them a hard sell in a region that regularly sees extended cold snaps. Modern units from manufacturers like Mitsubishi operate efficiently well below freezing — making them genuinely viable as primary heat sources, not just supplements.

Domestic hot water is included. A boiler replacement in a New England home usually means replacing domestic hot water production too. Many air-to-water systems handle both space heating and domestic hot water from a single unit, simplifying the replacement.

Oil dependence is a real financial risk. Heating oil prices in New England are notoriously volatile, and the region imports the vast majority of its fuel. Every year you stay on oil is another year of exposure to price spikes, supply disruptions, and a commodity whose long-term trajectory is upward. Locking in electrically-powered heat insulates you from that risk — especially if you’re generating your own electricity with solar.

The Mitsubishi Ecodan: Built for This

When it comes to air-to-water heat pumps engineered for cold climates, the Mitsubishi Ecodan is one of the most serious systems on the market.

Mitsubishi developed the Ecodan specifically for climates where winter temperatures regularly drop below freezing — not as an afterthought, but as the primary design requirement. The result is a system that performs where older heat pump technology fell apart.

How it works: The Ecodan outdoor unit extracts heat from the outside air using refrigerant, then transfers that heat to a water circuit via a heat exchanger. That circuit connects to your home’s existing heating distribution — radiant floors, fan coil units, or low-temperature radiators — as well as a domestic hot water cylinder. The system is managed by Mitsubishi’s MELCloud controller, which can be operated via smartphone and programmed for schedules, zones, and weather compensation.

Cold-climate performance: The Ecodan is rated to operate in ambient temperatures down to -13°F (-25°C). It uses Mitsubishi’s Zubadan technology — the same core platform behind their Hyper-Heat mini splits — to maintain efficiency even as outdoor temperatures drop. In real-world New England installations, this means the system keeps producing heat through January and February without needing a backup resistance element to carry the load.

Efficiency: Measured by its Coefficient of Performance (COP), the Ecodan consistently delivers 2.5 to 3.5 units of heat for every unit of electricity it consumes under typical operating conditions. Compare that to an oil boiler running at 85% efficiency, and the difference in operating cost is substantial — even before accounting for the difference in fuel prices.

Domestic hot water: The Ecodan integrates with a hot water cylinder to provide domestic hot water for the whole home. Some configurations include an immersion heater backup for peak demand, but day-to-day hot water is produced efficiently by the heat pump itself.

System flexibility: The Ecodan can be configured for a range of home sizes and loads. It works best paired with lower-temperature distribution systems — radiant floors being the ideal — but can also be adapted for existing baseboard and radiator systems with appropriate design. In some installations, a hybrid approach pairs the Ecodan with an existing boiler as a backup, allowing a phased transition.

Integration with solar: Like any electrically-powered heat pump, the Ecodan is a natural partner for a solar array. When your home generates its own electricity, the economics of operating an air-to-water system improve dramatically. We design Ecodan and solar installations together — sizing the array to cover the heat pump’s annual load, with battery storage available for homeowners who want to go further.

Is Air-to-Water Right for Your Home?

Air-to-water heat pumps aren’t the right fit for every home, but they’re the right fit for more homes than most people realize. The best candidates are:

• Homes currently heated with a hydronic system (radiant floors, hot water baseboard, or radiators) using oil, propane, or gas
• Homes where adding ductwork for a forced-air system would be expensive or impractical
• Homeowners who want a single system to handle both space heating and domestic hot water
• Homes paired with solar, where low operating cost over time is the priority
• Anyone committed to getting completely off fossil fuels

If you have a forced-air system, a standard mini split or air-to-air heat pump is almost certainly the better path. But if you have a hydronic home — and in New England, a lot of you do — air-to-water deserves a serious look.

What About Incentives?

The same federal tax credits that apply to mini splits apply to air-to-water heat pumps. The Inflation Reduction Act’s 25C credit covers 30% of the installed cost of qualifying cold-climate heat pumps, up to $2,000 per year. Utility rebate programs across New England — including Mass Save, NHSaves, and Efficiency Maine — also include air-to-water systems in their qualifying equipment lists, though program details and amounts vary by state and utility.

We help every customer understand exactly what incentives apply to their installation before they commit. For many homeowners, the combination of federal credits and utility rebates meaningfully reduces the upfront cost.

A Note on Installation

Air-to-water systems are more complex to design and install than a standard mini split. The system needs to be properly sized for your home’s heat load, the water circuit needs to be properly configured, and the controls need to be set up for your specific distribution system.

This is one reason working with an experienced, certified installer matters. We’ve invested in the training and certifications to install these systems correctly — which affects both your comfort and the long-term reliability of the equipment.

Curious Whether It Makes Sense for Your Home?

If you have a hydronic heating system and you’re tired of oil or propane prices, we’d love to talk. A free site assessment gives us a chance to look at your existing system, understand your goals, and tell you honestly whether an air-to-water heat pump is the right move.

Call us at 888-4-SUNDIAL or fill out our contact form to get started.

Sundial is a Mitsubishi Diamond Dealer specializing in cold-climate heat pump systems and solar installations throughout New England.