Geothermal Heat Pumps: Ground Loops, Drilling & IGSHPA

Welcome

Hello, and welcome. This is Super Structures General Contractors — a national general contractor headquartered in Powhatan, Virginia — here to help you and your clients build something that lasts. We're glad you're with us, and we look forward to connecting with you.

A few feet down, the earth stays at a fairly steady temperature all year — cooler than the summer air, warmer than the winter air. A ground-source heat pump uses that stable temperature to heat and cool a building with far less energy than conventional equipment. It's one of the most efficient systems a contractor can install, and it pulls together HVAC, plumbing-style piping, drilling, and electrical work.

Educational overview only — not electrical, mechanical, structural, or drilling design, a safety program, or a substitute for work under licensed electricians, mechanical contractors, well drillers, and engineers. Follow the NEC as adopted by your authority having jurisdiction (AHJ), the building, mechanical, plumbing, and fire codes, OSHA, state water and well regulations, the manufacturers' instructions, and your utility's rules. Code editions change and jurisdictions adopt different ones — always check the edition your AHJ enforces.

Not the Same as a Geothermal Power Plant

"Geothermal" means two very different things:

• Geothermal power plants tap high-temperature reservoirs deep underground — steam or hot water — to spin turbines and make electricity. They are concentrated where the geology allows (in the U.S., mostly in the West) and use dry steam, flash, or binary-cycle plants. Newer "enhanced geothermal" approaches aim to expand where that works.
• Ground-source heat pumps (also called geothermal heat pumps or GeoExchange) don't make electricity. They move heat between a building and the shallow ground, which works almost anywhere.

This lesson is about the second kind — the one contractors install in homes, schools, and commercial buildings.

How a Ground-Source Heat Pump Works

Inside the building, a heat pump uses a refrigeration cycle to move heat. Outside, a ground loop circulates water or an antifreeze solution through buried pipe. In winter, the fluid picks up heat from the ground and the heat pump concentrates it for the building; in summer, the heat pump rejects the building's heat into the ground. Because the ground is a much better heat source and sink than outdoor air at temperature extremes, efficiency is high — a coefficient of performance (COP) commonly in the range of about 3 to 5 in heating, meaning several units of heat delivered per unit of electricity, depending on equipment and loop temperatures.

Types of Ground Loops

• Horizontal closed loop — pipe laid in trenches, typically several feet deep, sometimes as coiled "slinky" loops. Cheapest when land is available; needs a lot of yard.
• Vertical closed loop — U-shaped pipe inserted in boreholes that are often a few hundred feet deep, then grouted. Fits small lots and commercial sites; drilling is the main cost.
• Pond or lake loop — coils sunk in a body of water deep and large enough to stay stable; economical where suitable water exists.
• Open loop — pumps groundwater from a well through the heat pump and discharges it to a return well or approved surface outlet. Efficient, but depends on water quantity and quality and is regulated for both withdrawal and discharge.

Closed-loop pipe is usually high-density polyethylene (HDPE) joined by heat fusion — not glued — because the loop has to last for decades underground.

Drilling and Loop Installation

A vertical loop job looks like a well job: a drill rig, mud or air drilling, cuttings and water management, and a crew that knows the local geology. After the U-bend is inserted, the borehole is grouted from the bottom up with a grout (often a bentonite-based or thermally enhanced mix) that conducts heat and seals the hole to protect aquifers. Then come header connections, pressure testing, flushing and purging air from the loop, and charging with fluid. Many states regulate geothermal boreholes under well or borehole rules — licensed or registered drillers, permits, setbacks from septic systems and wells, approved grouts, and approved antifreeze types. Check the state rules before you quote.

Design and IGSHPA

Loop length is designed, not guessed. It depends on the building's heating and cooling loads, soil or rock thermal conductivity, ground temperature, and the heat pump's performance. Larger projects often run a thermal conductivity test on a test bore. The International Ground Source Heat Pump Association (IGSHPA) publishes installation standards and offers training and accredited installer credentials, and designer credentials are available as well. Many utilities, owners, and specifications look for IGSHPA-trained installers.

Going Deeper (Intermediate)

An undersized loop is the classic failure: the loop temperature drifts too cold in winter or too hot in summer over several seasons, efficiency drops, and the heat pump may lock out. An oversized loop wastes money. Good installers also watch flow rates and pumping power — a loop with too much pump energy erodes the efficiency gains. Ductwork and distribution still matter; a great heat pump connected to leaky, undersized ducts will disappoint.

Advanced / Pro-Level

On commercial and campus work, pros design bore fields with spacing that prevents long-term heat buildup, model loads over decades, and consider hybrid systems (adding a cooling tower or boiler) to shrink the bore field. District or networked geothermal — shared loops serving multiple buildings — is a growing area. On federal incentives: the residential clean energy credit (§25D), which had covered geothermal heat pumps, ended for expenditures after December 31, 2025 under the July 2025 federal budget law; commercial treatment differs. As of late 2025 — rules and guidance continue to change; verify with a tax professional and current IRS guidance.

Practice Challenge

A homeowner on a quarter-acre lot wants a ground-source system. The yard can't fit horizontal trenches, and there's a private drinking-water well and a septic field. What's your plan? (Answer: a vertical closed loop, with a load calculation and loop design first; confirm the state's borehole rules and setbacks from the well and septic; use a licensed or registered driller; grout full-depth to protect the aquifer; and use an approved antifreeze. Coordinate the indoor HVAC work under the mechanical license and the electrical under the electrical license.)

In Practice

Successful geothermal contractors either own a drill rig or have a reliable drilling partner, and they schedule drilling early — it's the long pole and the messiest part of the site.

Common Mistakes to Avoid

• Sizing loop length from a rule of thumb instead of a design
• Confusing geothermal heat pumps with geothermal power plants in sales conversations
• Skipping full-depth grouting or ignoring well and septic setbacks
• Gluing or poorly fusing loop joints, or skipping the pressure test

Takeaway: Ground-source heat pumps move heat to and from the earth with remarkable efficiency — but only when the loop is designed, drilled, grouted, and tested to the state's rules and IGSHPA-level standards.