A house with radiators has no heating ducts, which is why the heat pump vs boiler question is really a question about where ducts could go. Clement Boston Heat Pumps converts boiler houses to ducted heat pumps across Boston and the inner suburbs, and sometimes recommends keeping the boiler for part of the job.
The two systems side by side
A boiler heats water or steam and sends it to radiators; a ducted heat pump moves heat into air and sends it through registers. Each is good at different things.
| Gas or oil boiler with radiators | Ducted cold-climate heat pump | |
|---|---|---|
| Heat delivery | Radiators or baseboard, warm surfaces | Registers, moving air |
| Cooling | None; window units or a separate AC | Built in |
| Fuel | Gas or oil burned on site | Electricity |
| Ducts | None needed | Needed: existing, added or small-duct |
| Running cost | Gas lowest; oil highest | Between gas and oil on the winter heat pump rate |
| Mass Save rebate | None for a new boiler | Whole-home or partial-home per ton |
| Typical life of the equipment | Long, especially cast-iron boilers | Shorter, because it runs year-round |
Why boiler houses are a different job
About 26% of Massachusetts homes heat with a steam or hot-water boiler. None of those houses came with heating ducts.
Where the ducts go
Ducts come from the top and the bottom of the house. An attic air handler serves the top floor through ceiling registers; a basement unit serves the first floor through the floor. Middle floors take a trunk run up a closet or chase.
Where there’s no room for standard ducts, a small-duct high-velocity system runs flexible 2-inch tubes through wall and floor cavities. It fits plaster walls and tight framing better, at a higher equipment cost. See heat pumps in older houses and our ductwork service.
What it costs to replace a boiler
The ducts make a boiler conversion the most expensive kind of heat pump job. Our typical range for a heat pump with new ductwork or a small-duct system is $20,000 to $40,000 and up before rebates.
What moves it
- How many floors need ducts, and whether the attic is open or finished
- Small-duct versus standard ducts
- Plaster openings and their repair
- The electrical panel, since a boiler house often still has 100-amp service
- Removing the boiler, capping the gas or removing the oil tank
The cost guide explains the rest of the price.
Running cost against oil and gas boilers
The fuel decides this part. Against an oil boiler, a heat pump on the winter rate delivers heat for far less; against a gas boiler, gas stays cheaper per unit of heat.
- Oil boiler: the strongest case for switching; see heat pump vs oil heat.
- Gas boiler: the switch rests on cooling, rebates and the boiler’s age more than fuel savings; see heat pump vs gas furnace for the same math.
- Steam boilers: usually less efficient than hot-water systems, which narrows the gap with a heat pump.
Three ways to approach a boiler house
You don’t have to choose all or nothing. Three plans fit most radiator homes, and each has its own rebate path.
Replace the boiler entirely
A whole-home heat pump carries all the heating, the boiler comes out (or stays only for domestic hot water), and the house earns Mass Save’s whole-home rebate. It’s the cleanest result and the biggest job.
Keep the boiler as backup
The heat pump heats most of the winter through new ducts and cools in summer; an integrated control hands off to the boiler on the coldest nights. Mass Save treats it as partial-home. Keeping some radiators live also keeps hot-water piping in exterior walls from sitting cold.
Add cooling and shoulder-season heat first
A single attic system on the top floor adds central cooling and carries spring and fall heat, while the boiler keeps doing winter. It’s a smaller first step that sets up a later conversion.
What happens to the radiators, pipes and hot water
Removing a boiler touches more than the boiler. The radiators, the piping in the walls and the household hot water each need a decision on the estimate.
Radiators and piping
If the boiler goes, the system is drained so no water sits in pipes along cold exterior walls, and the radiators can stay as decoration or come out room by room. If the boiler stays as backup, the zones that still run keep their water moving, which is the best protection against a frozen pipe.
Steam systems
Steam radiators run hotter and cycle harder than hot-water baseboard. Pairing steam with a heat pump works, but the control has to stop the two from fighting, and the boiler’s water level and venting still need their usual winter checks.
Hot water
Many boilers also make the household hot water through a coil or an indirect tank. If the boiler comes out, a separate water heater goes in; under the whole-home rebate, the boiler may instead stay for hot water only.
How to decide
Three facts usually settle it: the boiler’s fuel and age, whether you want central cooling, and how easily ducts fit. We measure the last one at the first visit, floor by floor.
If the boiler is oil, aging or both, and the attic and basement are open, replacing it with a boiler to heat pump conversion is usually worth it. If it’s a sound gas boiler in a house with finished attics, keeping it as backup is often the better buy. Call us or send the form to book the visit.