Converting a Gas Furnace to Geothermal in Wellesley, MA

In 2022, EnergySmart Alternatives completed a geothermal retrofit at a 4,100-square-foot home built in 2014 in Wellesley. The property was originally heated with a natural gas furnace and cooled with a traditional central air conditioning system.

Although the home was relatively new, the homeowner wanted to transition away from fossil fuels and take advantage of renewable energy. By replacing the existing HVAC system with a high-efficiency geothermal heat pump, EnergySmart helped the homeowner significantly reduce energy costs while creating a quieter, more efficient home comfort system.

This project demonstrates that geothermal systems aren’t just for new construction, they can also be an excellent upgrade for modern homes looking to improve efficiency and sustainability.

Why This Home Was a Strong Candidate for Geothermal

Several factors made geothermal an ideal solution for this retrofit project.

The Homeowner Wanted to Eliminate Fossil Fuel Use

The homeowner was looking for a long-term solution that would reduce dependence on natural gas and move the home toward cleaner energy.

Existing Solar Panels Reduced Operating Costs

Because the home already had solar panels installed, the electricity required to run the geothermal system could largely be offset by renewable energy generated onsite.

Aging Air Conditioning Equipment

The conventional AC system required repairs, making it a logical time to consider upgrading to a more efficient system that could provide both heating and cooling.

Adequate Space for Drilling

The property had sufficient space in the side yard to install the vertical boreholes needed for the geothermal loop system.

Installation Overview

To install the geothermal system, EnergySmart drilled two 6-inch diameter vertical boreholes in the side yard of the property. These boreholes serve as the underground heat exchange system that allows geothermal heat pump technology to transfer heat between the home and the earth.

High-density polyethylene (HDPE) geothermal piping was installed inside each borehole and sealed in place using geothermal grout to ensure long-term durability and efficient heat transfer.

The loop pipes were then brought into the home through two 3-inch core penetrations in the concrete foundation, approximately four feet below grade. Inside the mechanical space, the geothermal loops were connected to a variable-speed geothermal heat pump, which was flushed with an ethanol-based antifreeze solution to maintain safe operation during colder temperatures.

One of the advantages of this retrofit was the ability to reuse the home’s existing HVAC infrastructure. The original two-zone forced air ductwork system required only minor modifications before being connected to the new geothermal system.

Modern heat pump thermostats were installed with WiFi connectivity, allowing the homeowner to monitor system performance and control temperatures remotely through a mobile app.

System Performance and Operating Costs

The geothermal system has delivered strong performance while dramatically improving energy efficiency.

• Total 2025 Electricity Use: approximately 6,530 kWh
• Estimated Operating Cost: about $1,960 per year at $0.30/kWh

Because the home’s solar panel system offsets much of this electricity consumption, the effective cost of heating and cooling the home is extremely low.

For homeowners looking to reduce both energy bills and carbon footprint, combining geothermal with solar can create a powerful high-efficiency energy solution.

Benefits of Switching from Gas to Geothermal

This retrofit provided several immediate and long-term advantages for the homeowner.

One System for Heating and Cooling

A single geothermal heat pump now provides both heating and air conditioning, eliminating the need for separate systems.

Fossil Fuel Heating Eliminated

The natural gas furnace is no longer needed, reducing reliance on fossil fuels and lowering emissions.

Solar-Powered Efficiency

Electricity used by the geothermal system is largely offset by the home’s existing solar panels.

Quieter Outdoor Environment

The traditional outdoor AC condenser was removed, eliminating the noise typically associated with central air conditioning.

Improved Comfort and Efficiency

Variable-speed geothermal heat pumps provide steady temperature control, better humidity management, and improved overall comfort compared to traditional systems.

Remote Monitoring and Control

WiFi-connected thermostats allow homeowners to monitor energy usage and adjust temperatures from anywhere.

A Smart Retrofit for Modern Homes

Many homeowners assume geothermal systems are only practical during new construction. This Wellesley project shows that retrofitting an existing home from gas heat to geothermal can be straightforward and highly effective, particularly when existing ductwork can be reused.

For homeowners considering ways to reduce energy costs, improve comfort, and move toward a cleaner energy future, geothermal retrofits can provide long-term benefits that extend far beyond traditional HVAC upgrades.

EnergySmart Alternatives specializes in designing geothermal systems that work seamlessly with both new homes and existing HVAC infrastructure across Massachusetts.