The central air quit, the quote on your desk is for another cooling-only condenser, and you’re wondering whether to replace AC with a heat pump instead. Clement Boston Heat Pumps makes that swap on the ducts you already have, so the same system cools all summer and heats spring, fall and much of the winter.
Your furnace or boiler stays for the coldest days unless you decide otherwise. We size the heat pump for both seasons and price it after the home visit, because the cost depends on how much heating it takes over.
Isn’t a heat pump just an AC that heats?
Nearly. It has the same compressor, coils and refrigerant loop as an air conditioner, plus a reversing valve that flips the flow in winter so the outdoor coil gathers heat instead of shedding it.
In heating mode the outdoor coil runs below freezing, so frost builds up and the unit defrosts it every so often. Cold-climate models add variable-speed compressors that keep heating well below 0°F; a standard heat pump fades fast in deep cold. Our heat pump vs central AC guide compares them side by side.
Ratings to read on a quote
Cooling efficiency is rated in SEER2 and heating in HSPF2. For a Boston house that leans on the heat pump in winter, the heating rating and the output at 5°F matter more than the cooling number; see SEER2 and HSPF2.
What gets replaced besides the outdoor unit
The indoor coil, almost always. An AC coil wasn’t built or matched for heating, so the new outdoor unit gets a matched coil or air handler, and the controls change to manage two heat sources.
- Coil or air handler. On a furnace, a new heat-rated coil sits on top of it. In an attic, a new air handler goes in, because the old one is usually as old as the condenser that failed.
- Line set. Older AC lines carried R-22 or R-410A, and new equipment uses R-454B. We flush or replace the lines, pressure-test with nitrogen, pull a vacuum below 500 microns and weigh in the charge for the line length.
- Thermostat. A control that runs the reversing valve and decides between the heat pump and the furnace or boiler; see our thermostat guide.
- The outdoor spot. An AC sits on a ground pad. A heat pump runs all winter and sheds defrost water, so it goes on a stand above drifting snow.
- The circuit. Often reused when the breaker and wire suit the new unit’s nameplate; we check before counting on it.
If the AC sat on top of a furnace
The new heat-rated coil goes where the AC coil was, and the furnace stays as backup. A dual-fuel control chooses which one heats, usually by outdoor temperature, so they never run against each other.
The switchover temperature is the setting that matters. Set it low and the heat pump carries most of the winter; set it high and the furnace does. Our dual-fuel page explains how we pick it.
When the furnace is old too
If the furnace is near the end as well, replacing both at once avoids paying for a coil twice. That job is a furnace to heat pump conversion, with the furnace gone and a heat pump air handler in its place.
If a boiler heats the house and the AC lives in the attic
Here the attic AC has its own ducts to the top floor while radiators heat the house. Replace that AC with a heat pump and the top floor gets a second heat source that runs on electricity instead of the boiler’s fuel.
Attic ducts that only ever cooled now carry heat through the coldest space in the house. We seal joints with mastic, replace crushed or uninsulated flex with R-8 duct, and check that the ceiling registers can push warm air down to the floor. See attic air handlers for the platform, drain pan and access details.
Who heats what
The heat pump leads upstairs, and the boiler’s radiators follow on the coldest nights. We set the upstairs radiator thermostat a few degrees below the heat pump’s, so the boiler fires upstairs only when the heat pump can’t hold the setpoint. Downstairs stays on the boiler.
Sizing it for heat, not just cooling
An AC was sized for summer, and often oversized. A heat pump has to cool without short-cycling and heat well on cold nights, so we run the load both ways and choose a variable-speed unit that serves both.
In Greater Boston the heating load is normally the larger of the two. Where the heat pump only shares the heat, we size it to the cooling load and the floor it serves, then check how much of the winter it can carry. Our sizing guide shows the numbers.
Rebates when you replace AC with a heat pump
The rebate depends on what heat the heat pump displaces and how it’s controlled. Beside oil, propane or gas on integrated controls, Mass Save’s partial-home rebate can apply; a heat pump that only adds heat may fall to the basic tier.
If the furnace comes out, the job becomes whole-home. In light plant towns the town utility sets the rules: Belmont Light, for example, pays per ton for partial or whole-home systems after a home energy assessment, and Reading runs its own program. We confirm which tier your setup qualifies for before the estimate; the rebate guide has the amounts.
How long the swap takes
A condenser-and-coil swap on a furnace is usually one to two working days on site. An attic job with a new air handler and duct repairs runs closer to three, mostly for the attic work.
Summer is the busy season for AC, so a failure in July can mean a wait. Planning the change in spring or fall, while the old AC still runs, gives time for the load calculation and any rebate paperwork the town utility asks for first.