Heat naturally moves from warmer places to cooler places. Heat pumps use electricity to move heat from cooler places to warmer places, making the cool space cooler and the warm space warmer. Your refrigerator is a heat pump, moving heat from inside the refrigerated cabinet into your kitchen. An air conditioner is a heat pump, moving heat from inside your home to the hot outside summer air.

Heat pumps are also used to heat homes and businesses. While air-source heat pumps extract heat from the outdoor air, a ground-source heat pump (GSHP) takes advantage of the fact that a few feet below the earth's surface the ground remains at a relatively constant temperature. Depending on latitude, ground temperatures range from 45°F to 75°F. Like a cave, this ground temperature is warmer than the air above it during the winter and cooler than the air in the summer.  This leads to the exceptionally high efficiency of GSHPs.

GSHP systems consist of three parts: the ground-loop heat exchanger, the heat pump unit, and the air or water (hydronic) delivery system (ductwork or piping throughout a home or building). The ground-loop heat exchanger is a system of tubes called a loop, which is buried in the ground near the building. A fluid (usually a mixture of water and environmentally friendly antifreeze) circulates through the tubing to absorb or relinquish heat within the ground.

In the winter, the heat pump unit extracts heat from the heat exchanger and pumps it into the indoor air or hot water delivery system, moving heat from the ground to the building's interior. In the summer, the process is reversed, and the heat pump moves heat from the indoor air into the heat exchanger, effectively moving the heat from indoors into the ground.

There are different types of GSHPs, based on variations in the ground loop and indoor unit configuration.

Ground-loop heat exchanger. The ground loop is the heat exchange surface for your heat pump. A home will typically need several hundred to thousand feet of piping in the ground loop to provide enough heat in the coldest part of the year. Ground loops are divided into “closed” and “open” loops:

1. Closed- loop systems use a continuous loop of buried piping, typically made out of high density polyethylene. A closed-loop system will circulate a mixture of water and antifreeze that is not directly exposed to the environment. In New England, most closed-loop systems are installed in vertical configurations, in which the ground loop is run through multiple boreholes that are drilled several hundred feet deep (see below). 

Some closed-loop systems are installed in horizontal configurations, in which the ground loop is run through multiple trenches approximately 5 ft. deep and around 300-400 feet long (see below).

2. Open-loop systems can be used where there is a source of groundwater available on the property from a well. Instead of circulating an antifreeze mixture, an open-loop system pumps groundwater into the indoor unit for heat extraction before returning the water to the ground. Open-loop systems are typically cheaper to install and more efficient (due to the more consistent year-round temperature of groundwater), though they require a readily-available source of clean groundwater and may require additional permitting or environmental review.

The configuration of the indoor unit will also vary depending on whether you use ductwork (forced air) or a water (hydronic) distribution system:

• A water-to-air system connects your indoor heat pump to a central air handler and uses your home’s existing ductwork to distribute heating and cooling throughout the home. Some modifications to your ductwork may be necessary to make it suitable for a ground-source heat pump.
•  A water-to-water system connects your heat pump to your existing hydronic distribution system to provide heating. One or more air handlers (and perhaps some ductwork) is necessary to provide air conditioning.

There are numerous benefits to using GSHPs:

• Highest energy savings potential. GSHPs are the most efficient heating and cooling system available - even more efficient than air-source heat pumps. If you heat with oil, propane, or electric-resistance heat, you could save hundreds to thousands of dollars per year on your heating bill by installing a ground-source heat pump. No need to pay thousands of dollars just to get a gas connection to your home: a cleaner, more efficient alternative is already available.
• Greatly reduce your carbon footprint. As the most efficient clean heating & cooling technology available, GSHPs will greatly reduce your carbon footprint. Using solar PV or other renewable electricity sources can further offset emissions from the electricity powering your heat pump. If you’re looking for the most environmentally-friendly heating and cooling system, look no further.
• A clean, whole-home solution. Ground-source systems can offer a clean whole-home heating and cooling solution without requiring backup heating. Eliminate fossil fuel combustion and associated risks from your home entirely. Ground-source can also heat 40-50% of your home’s domestic hot water at no additional operating cost with an add-on.
• No exposed outdoor components. Unlike central air conditioners and air-source heat pumps, GSHPs have no visible outdoor components, for a more aesthetically pleasing appearance.
• Remote monitoring. GSHPs often come with remote monitoring systems. These allow the installer to receive alerts, diagnose problems and verify performance, only needing to come out to your home when hands-on maintenance is required.

While GSHPs can be a great fit for many homes and businesses, there are some potential drawbacks:

• High upfront costs. GSHPs are very expensive to install, with most residential systems in Concord costing at least $31,000 after incentives. It can be a number of years before energy savings pay back the difference compared to traditional fossil fuel or central AC systems.
• Landscaping considerations. GSHP systems require drilling or excavation in your yard or lot. Vertical-loop systems require less disruption to your property, though there will still be disturbance associated with the drilling process and moving drilling equipment around. Ask installers about options for minimizing disruptions and restoring landscaping after installation.
• Installation time. As system design and drilling/excavation is required, the ground-source installation process will typically take 2-3 months to complete from when you sign a contract. A GSHP system may not be well-suited for an emergency replacement.
• Ductwork installation or modification may be required. GSHPs can offer both heating and cooling, but may require modifications to existing ductwork, which may be impractical in some situations. While GSHPs can work with hydronic (hot water) distribution systems, they are not compatible with steam heating systems. Ductwork and/or air-handling units are required for your ground-source system to provide air conditioning.

GSHP retrofits can work in most homes. If you answer “Yes” to any of the questions below, a ground-source heat pump may be a good fit for you:

• Do you heat with oil, propane or electric resistance?
• Do you want whole-home central air conditioning and heating in one system?
• Are you concerned about the aesthetics of air-source heat pumps?
• Do you want the most efficient, environmentally-friendly system available?
• Is your boiler/furnace or central AC system 15+ years old?

Ground-source heat pumps are considered to be clean heating and cooling systems because they do not create heat, but rather they move existing heat from the ground into your building. This process is powered by electricity, which one can purchase or generate from carbon-free sources like solar, wind, or hydro. Electricity supplied by the Concord Municipal Light Plant was 54% carbon-free in 2018. That percentage will be even higher in 2019!

Yes. Ground-source systems can be installed with desuperheaters that can provide you with about half of a typical home’s annual hot-water needs. A ground-source heat pump operating in cooling mode will typically store unwanted heat in the ground. A desuperheater will use that waste heat to pre-heat your hot water before it enters your hot water tank. A desuperheater add-on will cost around $1,800 but will cost virtually nothing extra to operate.

Ground-source systems require relatively little maintenance. The ground loop is designed to last for up to 50 years or more, and no other components are exposed to the elements. Periodic checkups and filter changes are the most common maintenance requirements. Some adjustments to the system’s performance can be done remotely if a monitoring system is installed, without your GSHP contractor needing to come out to your home or business.

The ground loop piping is designed to last for up to 50 years or more. The indoor heat-pump unit has a life expectancy of around 20 years, similar to conventional heating and cooling systems. Some pumps, controls, or other components may require replacement sooner than the indoor unit.

A ground-source installation will typically take 2-3 months to complete from when you sign a contract. This includes:

• Rebate pre-approval (1-3 weeks). Your installer will submit your application to the Concord Municipal Light Plant (CMLP) for rebate pre-approval prior to commencing work.
• Equipment ordering (1-2 weeks). Once the rebate is approved, your installer will order the equipment for your home.
• Drilling/excavation, installation, and commissioning (4-5 weeks). Over this period of time, your installer will drill/excavate and install your system. After the installation is complete, the installer will commission your system and educate you on how to use your new ground-source system.
• Inspections (~2 weeks). This will depend on when tradespeople schedule the inspections and when inspectors are available to come out to your home.

While horizontal ground-loop installations require more space, a vertical ground-loop system may require as little space as your driveway.  A qualified installer will generally offer to assess your lot at no charge.

The cost of a GSHP system will range due to the customization needed for your home. For Concord homes, most ground-source systems installed have ranged from $31,000 to $36,000 after all rebates, state incentives and federal tax credits.

See our Guide to Heat Pump Incentives for a complete list of state and federal incentives available for GSHP installations.

The Concord Municipal Light Plant (CMLP) offers rebates of $625 per heating ton, up to $3,125, to its residential and small business customers in Concord when they install a GSHP that meets the program criteria. Residential GSHP installations in Concord are averaging 4 tons of heating capacity. Learn more here.  

Note: CMLP customers are not eligible for Massachusetts Clean Energy Center or Mass Save rebates.

The Massachusetts Clean Energy Center maintains a list of ground-source heat pump installers that participated in their former ground-source heat pump rebate program, which was available to electricity customers in communities served by Eversource and National Grid. CMLP customers are free to use installers that have participated in the MassCEC program.

The International Ground-Source Heat Pump Association and the New England Geothermal Professional Association maintain directories of GSHP professionals, including installers.

We suggest soliciting proposals from at least three ground-source heat-pump installers.

Keep in mind that for any type of home heating or cooling system to work well, it must be selected, sized, and installed properly.  The low-cost installer may not be your best option.

Consider asking the following questions:

Equipment

Will you determine my building’s heating and cooling design loads using ACCA Manual J for residential or Manual N for commercial, and size the equipment accordingly?

Qualifications and Experience

Can you provide documentation that you hold one of the following credentials?

• International Ground-Source Heat Pump Association (IGSHPA) Accreditation;
• Certification as a GeoExchange Designer (CGD) from IGSHPA; or
• Professional Engineer (“PE”) License from the National Society of Professional Engineers

Can you provide references from previous customers with similar systems in my area?

Rebate

Are you familiar with the application process for CMLP’s ground-source heat pump rebate and are you willing to complete the process for me?

Installation Process

• When would you be able to perform the installation and how long will it take to complete?
• Will you hire subcontractors to complete portions of the project? If so, what firms and what will they do?
• How much advance notice will we receive before contractors arrive to do work?
• Will you provide training for me on how to properly operate and maintain the system?
• What warranty do you provide for the systems you install?

Contact Jan Aceti, the Concord Municipal Light Plant’s Energy Conservation Coordinator, at jaceti@concordma.gov or 978-318-3151.