A heat pump can replace a boiler in many homes, but how depends on the distribution. You can feed the existing radiators or baseboard with an air-to-water heat pump, replace hydronic heat with ductless or ducted air-source heat pumps, or keep the boiler as backup in a hybrid design. The deciding factors are the home's Manual J heating load, whether the existing emitters can heat each room at lower water temperatures, and how the house makes hot water.
The short version: a heat pump usually wins on operating cost and emissions when the house has a reasonable load and enough emitter, or when you are willing to change the distribution. A new boiler can still be the right call for a high-load house with small radiators and no budget for envelope work. A hybrid splits the difference. Whatever you recommend, show the homeowner the options you ruled out and the reason, so the recommendation reads as engineering rather than preference.
This guide is in outline form. The full version will include room-by-room emitter checks and cost comparisons.
In this guide
The options for a hydronic home
- New high-efficiency boiler.
- Air-to-water heat pump on the existing distribution.
- Ductless or ducted air-source heat pumps.
- Hybrid: heat pump first, boiler for the coldest hours.
Sizing from the load, not the old boiler
- Why boiler nameplates are a poor guide to the load.
- Running a room-by-room Manual J.
- Capacity at the heating design temperature under Manual S.
Can the existing emitters run at lower water temperatures?
- Comparing each room's emitter output with its heating load.
- Cast iron radiators vs fin-tube baseboard vs radiant floors.
- When to add emitter, and when to switch to air-source.
Domestic hot water
- Indirect tanks and tankless coils.
- Heat pump water heater options.
Rebates and eligibility
- NYS Clean Heat air-to-water heat pump qualified product list requirements. See the NYS Clean Heat contractor guide.
- Mass Save whole-home and partial-home rules. See the Mass Save contractor guide.
Steam systems
- Why steam homes are different.
- Common conversion paths.
Run the numbers
Estimate boiler output with the boiler sizing calculator, or per-zone head sizes with the mini split sizing calculator. Both give estimates only.
Tradewright prices a boiler, a heat pump and a hybrid option side by side on 15-year cost in one proposal. See system comparison and the oil boiler replacement options guide.
Questions
Can a heat pump replace a boiler?
Yes, in many homes. The options are an air-to-water heat pump that feeds the existing hydronic system, air-source heat pumps (ductless or ducted) that replace the hydronic distribution, or a hybrid that keeps the boiler for the coldest hours. The right answer depends on the load, the emitters and the budget.
Will my radiators work with an air-to-water heat pump?
Heat pumps are most efficient at lower water temperatures. Whether existing radiators or baseboard can heat each room at a lower supply temperature depends on how much emitter the room has compared to its Manual J heating load. Check room by room.
Are air-to-water heat pumps eligible for NYS Clean Heat?
Under the September 2026 program manual, residential air-to-water heat pumps must be on the NYS Clean Heat AWHP Qualified Product List. The manual states the list requires a heating COP of 1.7 or greater at 5°F ambient and 110°F leaving water temperature.
Should I size a heat pump to the old boiler's output?
No. Old boilers are often oversized. Size to a Manual J heating load at the local design temperature, then select equipment on its capacity at that temperature.
What about domestic hot water from the boiler?
If the boiler also makes hot water through an indirect tank or a tankless coil, the replacement plan must cover hot water too. Options include a heat pump water heater, an air-to-water heat pump with a tank, or keeping a dedicated water heater.
Sources
- NYS Clean Heat Heat Pump Program Manual, Version 3 (September 1, 2026), Section 3.1.1.2 Air-to-Water Heat Pumps (accessed 2026-10-16)
- NEEP: Guide to Sizing and Selecting Air-Source Heat Pumps in Cold Climates (accessed 2026-10-16)
- Mass Save: Air Source Heat Pump rebates and eligibility (accessed 2026-10-16)