6 - Heating and Cooling with Air Source Heat Pumps

Electrify Brookline | How-To Guide #6

Having a home that’s comfortably warm in the cold months and comfortably cool in the heat of the summer is undoubtedly a top priority for many. Do you have some rooms that just don’t get warm enough in winter? Do you use noisy window air conditioners and still swelter in the summer?

If your current heating system is nearing the end of its life, if you’re thinking about installing central AC, or if you just want a few rooms to have better heating or cooling, it’s time to consider air source heat pump technology.

What Is an Air Source Heat Pump?

Heat pumps move heat into and out of a building – much like an air conditioner or a refrigerator that can also run backwards to provide heating. When the weather is hot, they pump heat from the inside to the outside to cool things off. When it’s cold outside, they pump heat from the outside to the inside to warm your living space. Even when it’s really super cold, there’s still heat that can be pulled from the outside air to warm your rooms.

Heat pumps don’t create heat – they move heat. Since it takes far less energy to move heat than it does to create heat, heat pumps are one of the most efficient home heating and cooling systems available. Air source heat pump technology can be installed in many different ways: you can do your whole house, or just a floor, or just a room or two; you can install a system providing heating and cooling through air ducts, or one that delivers heating and cooling through wall or floor-mounted units, or a combination of approaches. Installing heat pumps not only makes your home comfortable, but it will help reduce harmful greenhouse gas emissions and reduce your dependence on fossil fuels – a win-win-win for improving the climate and improving your home comfort.

“A heat pump is probably the biggest thing that consumers can do to help fight the climate crisis,” said Amy Boyd, director of policy for the Acadia Center, a regional research and advocacy organization focusing on clean-energy policy in the Northeast.

How Can This Help the Climate?

A graph of household energy use in Massachusetts: 59% space heating, 24% Appliances & Lights, 16% water heating, 1% air conditioningThe information in this chart is from Household Energy Use in Massachusetts, page 1, EIA (U.S. Energy InformationAdministration).

Emissions from residential buildings in Massachusetts come from a variety of sources, as shown in this graph of Household Energy Usage in our state. The emissions from your home can be hard to see, but the biggest source by far is the furnace or the boiler that provides your home heating.

Air source heat pumps are all-electric and highly efficient – and they create ZERO space heating or cooling emissions if you sign up for 100% Green Electricity.

What’s Involved?

Air-source heat pump systems (ASHPs) feature an outdoor condenser unit connected to one or more indoor units by refrigerant piping. The refrigerant is a substance with properties that enable it to easily absorb and release heat.

A heat pump installation can be a straightforward process with minimal disruption to your home. A simple, single-zone ductless ASHP system can be completed in less than a day and only requires a single 2-3 inch hole to be cut (and later, sealed) in your home’s exterior wall.

If you are installing a “multi-zone” ductless system or a ducted system that requires modifications to existing ductwork or brand new ductwork, your installation may take a few days or more to complete.

Outdoor condenser units come in different sizes depending on the heating load required. Your contractor or installer should collect data on the number and size of the rooms, size and type of windows, exterior wall and roof insulation, etc in order to determine the heat load of each space in your home and the required unit size that will meet the need. Oversized and undersized systems will not function well or work most efficiently, so proper sizing is an important step. If you’d like to know more about Manual J Load Calculations and how they work, consult indeed.com.

heat pump showing unit off the ground

Outdoor units should be mounted on metal stands that are at 12”, 18” or 24” high to ensure they will be above snow, and located to minimize snow build-up from drifting during storms or from sliding off of roofs above. Outdoor units can also be wall-mounted where ground space is limited, but may lead to noise or vibrations transmitted inside the building walls. 

Note: Exterior equipment may also require Preservation and/or Zoning approval.

What Choices Are There?

Heat pumps are a flexible technology that can be installed in homes of all shapes and sizes with different needs – whether you need a whole-home system, have (or don’t have) ductwork, want to add zoning to your home, want to increase the efficiency of heating in part of your home, or want to add extra heating/cooling to that part of your home that’s never as comfortable as it should be. Air source heat pumps can be “ductless” or “ducted” or use a combination of the two types of systems.

Ductless heat pumps are exactly as they sound: heat pumps that don’t require that you have ductwork in your home. They require one or more outdoor condenser units connected to one (single-zone) or more (multi-zone) indoor units to distribute the heating or cooling. The closed-loop refrigerant running to and from the outdoor unit is connected to the indoor units via piping that runs inside or outside your home. These systems are often referred to as ductless mini-splits or just mini-splits.

Ductless indoor units can be wall-mounted, on the floor or in your ceiling. Wall units, which are typically mounted near the top of a room’s wall, are the most common option; floor-mounted units can often replace the location of old radiators.

Ductless air source heat pumps can be installed as a home’s primary source of heating and cooling, or installed to heat and cool specific areas or specific rooms. Because each indoor unit can be controlled individually, you can reduce your energy use even more by lowering the heating setpoint in rooms that are not being used.

Ducted (or centralized) heat pumps have an outdoor condenser unit with a refrigerant piping loop that is connected to an indoor air handling unit that distributes heating or cooling air via a building’s existing or new ductwork. Sometimes these systems are called “ducted mini-splits”, as they require indoor and outdoor equipment in addition to the ducts. Ducted heat pump systems will typically have air vents with grilles located at the floor, wall or ceiling in each room.

Ducted heat pumps may be able to use your home’s existing ductwork if you have a forced hot air heating system or a centralized AC system, but sometimes the existing ductwork may not be the correct size, or may be inadequately insulated or sealed. An installer can tell you if your current ductwork can be re-used and what modifications may be necessary. Ducted systems can be more flexible in their design, and sized to deliver the correct amount of air to each separate room.

When you’re buying something as expensive and long-lasting as a heat pump, you should make sure the equipment is from a manufacturer that has a good reputation and can provide you with quality customer support for years to come.

More often than not, your contractor or installer will be the one sourcing the heat pump system components. There may be some models that have better energy efficiency, or better equipment distributors in certain geographic regions. Generally speaking, it’s better to find a good contractor first and then take advantage of their expertise with the brands and models that they’re familiar with.

Some resources for finding products:

Other Considerations

  • Concerned about heat pump performance in winter? Today’s cold climate air source heat pumps can extract heat from the air all the way down to at least -13°F, but you’ll want to make sure the system you have is sized appropriately for your home. To find air-source heat pumps that are certified as cold climate heat pumps, look at NEEP’s Cold Climate Air Source Heat Pump List.
  • Before you start a heat pump project, schedule a no-cost Mass Save Home Energy Assessment; understanding the assessment and completing the weatherization recommendations is required for eligibility for some of the Mass Save rebates.
  • If you are planning on accessing rebates, incentives and tax credits from Mass Save or the IRS, be sure to review the program details to verify that the heat pump products specified will meet the minimum program requirements.
  • If your home is in a designated Local Historic District (LHD) in Brookline be sure to understand the specific restrictions on locating exterior equipment, piping and electrical lines. The guidelines require that, when possible, renewable energy systems should be proposed for installation in locations where they will not be visible from a public way, park or body of water. In cases where this is not practicable, systems attached to buildings should not obscure historic features from public view, or be visible in a way which significantly alters the profile or character of the building.
  • Advanced heat pumps are “variable capacity,” which means they can provide just the right amount of heating or cooling without temperature swings and constantly turning on and off. The typical lifespan of a heat pump is the same as a conventional furnace or central air conditioner. Annual system maintenance consists of cleaning air filters (which you can clean yourself) and an optional annual maintenance checkup for the outside unit. The cost is about the same as annual servicing charges for a boiler or furnace.
  • In addition to providing heating and cooling, heat pumps filter and dehumidify air, which can improve the air quality and comfort of your home. In particular, the filtration provided can significantly reduce allergens in your home for sensitive individuals.
  • Outdoor units should not be installed right next to a dryer vent or directly below where you typically have ice dams that form on your roof, as falling ice can cause damage. The units require sufficient space above and around to allow for air to circulate, but in some cases may be able to be hidden under a high porch, or encircled by bushes and shrubs.
  • Air source heat pumps allow you to reclaim your windows and avoid having to install window A/C units each summer.

Note: In addition to air source heat pumps, there are also ground-source heat pumps (GSHPs) that use the relatively constant temperature of the earth well below grade to heat or cool the refrigerant loops. These systems require drilling of deep wells or sufficient outdoor space to bury a system of horizontal loops; GSHP systems tend to be more expensive to install than air-source heat pumps, but can cost less to operate.


Installation Costs: Air source heat pump systems typically start at several thousand dollars before incentives for a single-zone unit, increasing with additional zones. Pricing is higher if you are installing a whole-house heat pump as the primary heating/cooling system for the home, and systems will likely be more costly as square footage, number of rooms in the home and complexities like installation of ductwork increase.

Green Energy Consumers Alliance estimates that the average whole home heat pump system in our region is running around $15,000 - $25,000, but the cost depends on what percentage of your heating the heat pump will provide, how large your home is, and how well-insulated it is. A heat pump for a relatively small, well insulated house might cost only $6,000, but a larger, under-insulated home might cost $45,000.

Note that 200 amp electrical service may be needed for heat pump installation. Upgrading to 200 amp service if you do not currently have it could be an additional cost.

Operating Costs: If you have radiant electric heating or use electric space heaters, heat pumps are 2-4 times more efficient and can save you thousands of kWh, and hundreds of dollars, every year. If you have gas or oil heating, the cost difference between burning fossil fuels and using an air source heat pump will depend on a number of variables, including the price of gas, the price of electricity, and whether you have rooftop solar or another means of generating electricity.

The seasonal efficiency of ASHPs can range from 220% to 300%+ depending on the system type, application, and how cold it is outside. That means that for every one unit of electricity used, 2.2 to 3 units of heat are transferred into the home. By comparison, many fossil fuel boilers and furnaces are 80% efficient, with even the most efficient models never more than 98% efficient.

Questions Around Electricity

If you have 100-amp electrical service you may need an upgrade, depending on the size and type of heat pump you’re installing and what electric appliances you currently have. If your electrical service is sufficient but your circuit breakers are full, you may need to add a subpanel to make room for new circuit breakers for the heat pump.

Ask your electrician to assess the current state of your electrical service and make recommendations regarding whether an upgrade might be needed for the heat pump solution that meets your needs. The cost of electrical work may range from a few hundred to several thousand dollars, depending on whether you need to upgrade your breaker box or the electrical service to your home.

Available Rebates and Tax Credits

State rebates from Mass Save of up to $10,000 are available for partial systems, where a heat pump is combined with a fossil fuel primary heating system. A rebate of $10,000 for whole house systems is available regardless of system size – if you have a small home or condo, or if you are a landlord upgrading individual rental units, this rebate for each dwelling unit can cover a good part of the installation costs.

Federal monies through the Inflation Reduction Act (IRA) provide a 30 percent tax credit for heat pumps and heat pump water heaters, capped at $2,000 per year. The credit resets each tax year, effectively becoming available again for additional projects. This tax credit is available now! The new IRA will also provide a tax credit of up to $600 for electrical upgrades if done in conjunction with installing heat pumps or a heat pump water heater.

Another good resource is the Massachusetts Clean Energy Center, which includes a table on available incentives from both our state and the federal government.

There is also good information on the energy.gov website.

Need Some Advice?

Green Energy Consumers Alliance (GECA), a Massachusetts-based non-profit, has excellent resources to help you understand and learn about air source heat pumps.

  • Get Advice on heat pumps.
  • Sign up for GECA’s heat pump referral list and other services from Abode. Abode, an energy management company based in Concord, MA, has made an alliance with Green Energy Consumers Alliance and provides a service to review and compare up to three proposals for heat pumps for installers. If you access Abode from the GECA website, this service is offered at half price.  
  • Watch a one-hour webinar recorded on YouTube discussing heat pumps.

The Town of Brookline is including the link to Adobe for informational purposes only It has no association with Abode and makes no claims, representation, endorsement or warranty (express or implied) about the quality of the services it provides.

The Massachusetts Clean Energy Center, a state agency focused on the clean energy sector, has good information about heat pumps.

There is an excellent article from NYTimes’ Wirecutter on heat pumps.

Rewiring America provides an excellent guide “Go Electric”.

And finally, here’s an article from Will Brownsberger, State Senator from Belmont on his experience installing heat pumps and getting rid of gas service to his home.

How Your Neighbors Made the Switch

Story #1: – An Early Adopter of Mini-Splits

Owners of a single-family home purchased in 1993 in North Brookline cared deeply about the environment and wanted their house to be as energy efficient as possible. Their motivation to install mini-split air source heat pumps was two-fold: they hated the window air conditioners they had, and they wanted to make their house environmentally friendly. About those air conditioners: there were window units in each of their four bedrooms and one in the living room. The homeowners really didn’t like the noise, they didn’t like the quality of the air, and they didn’t like how much electricity it was costing them. It had to be a really uncomfortable night before they would turn any of them on.

The mini-splits have solved this problem completely – the cool air they produce in warm weather is fantastic. They’re not noisy, they’re incredibly efficient and the electricity bill is way, way down over the summer months.

What about heating? The mini-splits help with that too. The homeowners installed them a little over ten years ago, when there was concern that the system might not be able to provide enough heat in the extremely cold weather.* So they kept their old boiler and radiators as a backup system, setting the thermostat at 58o, and they continue to use a gas hot water heater. At the time of the installation, they were able to finance the project with a 0% loan.

Now they’re able to target room by room what gets heated above that. They have three mini-splits on their first floor – one each in the living room, dining room, and kitchen – and four mini-splits on the second floor – one in each of the four bedrooms – with two external condensers to drive the units. Their kids are grown and out of the house, so some rooms are rarely used and don’t need to be as warm as the rooms that are used more regularly.

The system is reliable and easy to maintain. It’s simple to remove the filters, rinse them in water, and then slip them back in.

*According to a Consumer Reports article from August 2022: “But that’s old news. When properly installed, plenty of today’s air-source heat pumps...can keep your home toasty even amid bone-chilling cold, using far less energy than other types of heating systems.”

Story #2: A Combination of Ducted and Ductless Heat Pumps

These homeowners bought their house in the Brookline Village area in 1993. It’s about 1,500 square feet total on the 1st and 2nd floors, with about 400 square feet additional in the partially finished basement. 

Around 2010 the family started looking into the support that Mass Save provides for home energy assessments and improvements. Whatever energy efficiency rebates and incentives Mass Save offered, the homeowners wanted to access. They insulated their walls and their attic using Mass Save rebates and when they replaced their old boiler with a high energy efficiency model, they also received Mass Save rebates. 

They kept going, installing new insulated windows and putting solar panels on their roof in 2017, accessing additional state and federal incentives and tax credits. 

For cooling in the hot days of summer, they were using one window air conditioner on the ground floor and several more window air conditioners in the 2nd floor bedrooms. The window units were noisy, they were hard to put in and out of the windows, they did not cool the whole house, and they were not energy efficient. So when they started learning about heat pumps for heating and cooling, it seemed a logical step to explore, especially given the inadequate window air conditioners. 

They started getting quotes in summer 2021, and ended up with quotes from four installers. The prices ranged from $30,000 to $50,000 for the whole home system. They found the installers by looking at the MassSave list of approved installers, but probably more importantly, they received recommendations from their neighbors. By speaking with several installers, the homeowners learned quite a bit and were able to go back and forth between installers to discuss various options. They decided to go with an installer who’d been referred to them both from a contractor in the neighborhood and an architect-neighbor. 


The homeowners decided on a two-system installation: a ducted system for the second floor with the air handler and insulated ductwork in the attic, along with ductless mini-splits for the first floor and finished part of the basement. Since they were doing a whole-home system, they applied for the Mass Save rebate of $10,000, significantly reducing the net cost of installation. They decided to keep their existing boiler and radiators as an emergency back-up – they set those thermostats at 50 degrees, which complies with the Mass Save program requirements for the whole home rebate. Their gas bills are now minimal, covering just the account connection fee and the gas use for the indirect water heater only. 

The ducted system in the attic feeds vents and returns in each of the second floor bedrooms. Two mini-splits on the first floor make all the first-floor rooms comfortable. The mini-split in the basement has made the finished part of the basement comfortable all year round and can now be used for guest sleeping during the hot, muggy summer. There are two exterior condensers – one for the attic ducted system for the 2nd floor and the other for the 1st floor and basement mini-splits. Each outdoor condenser has a “cap” – an off-the shelf product that attaches to the stand to prevent damage in case snow or ice falls from the roof. 

Some observations from the homeowner: 

  • It was extremely helpful to talk with the four contractors and get their ideas and their quotes. It takes time, but the investment in both time and money has been more than worth it in terms of comfort, reliability and confidence. 
  • It can be tricky to size the system – the general advice is not to get more capacity than you need as these systems aren’t as efficient if they’re oversized. 
  • You can do this work incrementally. The homeowners could have done just the ducted system first, for example, and waited to do mini-splits later. Or they could have installed one or more mini-splits to start. The technology affords lots of options. 
  • The system is so efficient and so quiet that the homeowners say they don’t even know it’s running. 
  • It’s a two-fer – heating AND cooling. With our summers predicted to get warmer and warmer, and with more people working at home, the cooling for hot days becomes increasingly important. They can now use their whole house throughout the year; before, parts of the house had been too hot to use comfortably all summer. 
  • The homeowners are now installing a whole house heat pump system in a second house on the Cape to replace a conventional AC system past its useful life. They found that using the home’s existing ductwork will reduce the cost. Also, they will have just one single system to maintain for heating and cooling, and will not have to separately update a boiler for heat and an AC condenser for cooling.

About Electrify Brookline

Electrify Brookline is a collaboration between the Town of Brookline’s Zero Emissions Advisory Board (ZEAB), Mothers Out Front Brookline (MOF) and Climate Action Brookline (CAB). Our goal is to provide clear information to guide the community on the path toward electrification – improving the energy efficiency, health and comfort of their living spaces while reducing climate-damaging emissions to preserve a livable future for all.

IMPORTANT: Verify with your installers that they have the proper licenses and insurance, and confirm that they have or will obtain all required permits and inspections from the Town of Brookline.

These How-To Guides may contain links to other public or private organizations. The Town of Brookline does not guarantee the accuracy of information on other organizations’ sites to which this guide links. Links to any product, process, or service by trade name, trademark, manufacturer, or otherwise does not constitute or imply any endorsement, recommendation, or association with those sites, the material contained therein, or the sponsoring entities by the Town of Brookline or any of their officials, appointees, boards, agents, and employees. The Town of Brookline makes no claims, no representations, and no warranties (express or implied) about the validity, affordability, accuracy, or viability of any products or services offered by any such organizations. The Town of Brookline disclaims any liability stemming from errors or omissions in the contents of these sites, or for any improper or incorrect use of their contents. The burden for determining the accuracy or appropriateness of information on these sites rests solely on the user accessing the information. The contents of these sites are not owned or controlled by the Town, and the Town disavows any legal responsibility for the opinions expressed on them.