When we decided to turn a mostly-unused third story into a living area six years ago, we needed a way to cool it efficiently. It’s a large space with a 15-foot ceiling, and 95 degree days happen often enough in summer to make sleeping without air conditioning really difficult. Up until then we’d managed with a few window units and a bunch of fans in our house’s smallish second floor bedrooms. Rather than drop thousands of dollars on a central air conditioner, we started researching home geothermal energy systems, and we are thrilled we did.

What Is a Geothermal Energy System?

Also known as “ground-source heat pumps,” geothermal systems use long loops of fluid buried below ground to exchange heat with the surrounding soil. A few feet down, the soil remains a fairly even temperature year round. This means that in winter, warmth from the soil can be brought into your home, and in summer, excess heat can be deposited there.

We first heard about these systems from an energy auditor, who in addition to showing us the numerous ways we could increase our home’s energy efficiency, walked us through the various alternative energy options available to us. He gave us a rundown of the advantages and costs of solar hot water, solar photovoltaic systems, and two kinds of heat pumps—air- and ground-source. The numbers he used in describing these alternative heating methods immediately piqued my interest. While a high-efficiency natural gas furnace may work at 93% efficiency, an air source heat pump worked at 180%, and a ground source heat pump might achieve 400% efficiency. What did that even mean? How could something be more than 100% efficient?

In a nutshell, this is a way of measuring how much energy you can make with the energy you put in. With standard heating systems, the best you can hope for is getting out as much energy as you input, and most systems fall short. Because heat pumps simply move heat rather than burning fuel to create it, a geothermal system can harvest up to four times as much energy than you use to run it. Depending on the fuel used for your current heating system and what type of fuel powers your local electricity, the savings in carbon emissions can be significant, up to 5 tons per year. If you’re currently heating with natural gas and your electricity comes from burning coal, on the other hand, the carbon savings could be negligible. But with so many options for clean electricity, that’s easily remedied, either with panels on your own roof, through a community solar garden, or through a clean-power purchase plan.

How Do You Install a Geothermal System?

Installing a geothermal system can be somewhat involved. The heat-exchange loops that go into the ground are hundreds of feet long, which can mean some serious drilling and disruption to your landscaping. If there isn’t much land to work with, the wells are drilled vertically, the most labor intensive and expensive option. Loops that run horizontally cost significantly less to install but will disturb more landscaping. If you live next to a lake or pond, look into using that as your source for heat exchange, and costs may be smaller still. Once the loops are in place, they are tied to pipes that bring the heated or cooled liquid into your house, where they attach to the pump system that will heat and cool your home.

When installing a home geothermal system, drilling rigs for vertical loops can fit in tight spaces.

We live on a small lot with lots of fruit trees, so there weren’t very many options for where to drill wells. One area next to the house covered with creeping Charlie was just big enough for the five vertical wells our system needed. When the drilling was done, the soil was replaced, and we built some raised beds to grow annual vegetables and herbs. No one can tell that the wells heating our house are buried underneath.

The Pros and Cons of Geothermal Energy

Besides some substantial cost savings, geothermal has some additional benefits. The heat comes out at a lower temperature than forced air and runs continuously, so you don’t have major temperature swings. Geothermal systems are also routinely tied into hot water heaters, so heat that’s not needed for the house can heat water instead. They also cool without the noise of outdoor units.

We were lucky to take advantage of a 30% federal tax credit that brought down the price of our system considerably. These incentives were recently renewed and are as follows: 30% until 2019, 26% in 2020, and 22% in 2021. Incentives expire at the end of that year. The tax credit also applies retroactively for 2017 installations. If you have average or low electricity costs and are paying for more expensive heating fuel, payback will be quicker than if you have high electricity costs and low-cost heating fuel. And if you’re about to spend thousands replacing an older furnace or air conditioner, putting that money toward a geothermal system will very likely save you in the long run. You may also find state incentive or loan programs. Check what’s available in your area through the Database for State Incentives for Renewables and Efficiency (DSIRE).

According to the US Department of Energy, the payback period (how long it will take to recoup your investment in energy savings) on most geothermal systems is 5-10 years, which is comparable to solar’s payback timeline. The loops are typically guaranteed for 50 years, and the components inside the house 25 years. This is considerably longer than conventional furnaces and air conditioners.

According to the US Department of Energy, the payback period on most geothermal systems is 5-10 years, which is comparable to the payback timeline for solar energy.

In winters as extreme as ours, geothermal systems may not always provide enough heat, but that depends on your habits. We keep our house pretty cool, so we haven’t often switched on our backup heat (a high-efficiency gas furnace). On days when the outside temperature stays below zero, even though the geothermal keeps chugging away, it just won’t get above 62 or 63 degrees. But because the heat’s so even, we don’t really notice, and we could choose to use our back up heat if we wanted. In less extreme temperatures, geothermal systems should have little trouble heating a house.

Deciding Whether Geothermal Is Right For You

If you’re on board with renewable energy and doing right by the planet, a geothermal energy system might be the right choice for your home. Geothermal might also be an especially smart investment if:

• You’re about to replace your furnace or air conditioner
• You live on a large lot with a lake or pond
• You have high costs for heating or cooling
• You have local incentives that bring down the sticker price
• You plan to stay in your home long enough to recoup the investment

If geothermal doesn’t pan out for you, a far cheaper option that’s still more efficient than traditional heating fuels is an air source heat pump, which exchanges heat with the air. Like geothermal systems, air-source heat pumps work for both heating and cooling, which means if you’re thinking of replacing a whole-house air conditioner, an air-source heat pump may be a smarter choice. They don’t cost much more than air conditioners, and they’ll cool and heat your house far more efficiently. One limitation: air source heat pumps lose efficiency in colder weather and stop working when temperatures fall below 20 degrees, so those of us in colder parts of the world can’t use them for much of the winter.

Be sure to get quotes from multiple companies. It’s also wise to get an energy audit, add insulation, and check that your home is well sealed. Then enjoy the knowledge that you’re saving money and drastically reducing your home’s carbon emissions for years to come.