Geothermal Heat Pump Diagram: Every Component, Where It Sits, and How the Heat Moves

Search for a geothermal heat pump diagram and you get boxes and arrows: a squiggle of pipe under a house, a cabinet in the basement, ducts overhead. What the picture rarely explains is what each box actually is, which fluid runs through which pipe, and where one circuit ends and the next begins. This page is that diagram in words: every component named, placed, and connected, using the terminology the Department of Energy, ENERGY STAR, and the equipment manufacturers themselves use.

One warning before the first label goes on. A geothermal diagram has one boundary that decides whether the drawing is right or wrong: in a conventional closed-loop system, the refrigerant stays inside the indoor unit, and the buried loop carries water or a water-antifreeze mix. Diagrams that show refrigerant snaking through the yard are drawing a different architecture, direct geoexchange, which ENERGY STAR treats as its own equipment category. They usually don't say so. We'll put that line exactly where it belongs.

Which System This Diagram Draws

There is no single universal geothermal diagram, because there is no single geothermal architecture. This page draws one specific configuration: a residential closed-loop water-to-air packaged system. That means a sealed loop of buried plastic pipe outside, ducted air inside, and all of the machinery (compressor, heat exchangers, blower) in one indoor cabinet.

Other builds exist, and their diagrams differ in real ways:

• Split systems put the compressor section in a separate cabinet from the air handler, connected by refrigerant piping. They get their own section below.
• Water-to-water systems deliver heat to hydronic piping (radiant floors, for example) instead of an air coil and ducts. Our guide to water-to-water geothermal heat pumps covers that branch.
• Open-loop systems pump groundwater through the heat pump and return it, rather than recirculating a sealed fluid. See our guide to open loop geothermal systems.
• Direct geoexchange (DGX) circulates refrigerant through buried tubing with no water loop at all. It is the one architecture where refrigerant genuinely does go underground.

If you're still deciding which of these applies to your project, start with what a geothermal system is, which maps the full set. Everything below describes the closed-loop water-to-air packaged build unless it says otherwise.

The Three Blocks Every Diagram Starts With

The Department of Energy defines the system in exactly three parts. In DOE's words, a GHP system includes:

1. "An underground heat collector" — "a series of connected pipes buried in the ground near a building. The loop can be buried either vertically or horizontally. It circulates a fluid that absorbs or deposits heat to the surrounding soil."
2. "A heat pump" — which "removes heat from the collector's fluids, concentrates it, and transfers it to the building," and runs the process in reverse for cooling.
3. "A heat distribution subsystem" — "Conventional ductwork is generally used to distribute heated or cooled air."

Note DOE's own hedge in that third block: ductwork is "generally used," not always used. Hydronic delivery is the other option, which is why ENERGY STAR's more technical vocabulary for the same anatomy reads "ground heat exchanger(s)," "air and/or hydronic space conditioning distribution system(s)," "temperature controls," and "thermal storage tanks." For water-to-air equipment specifically, that vocabulary also includes the "indoor air heat exchange coil."

So the diagram's top-level layout is three blocks in a row: ground loop → indoor unit → ducts, with a thermostat wired to the middle block. Every other label on the page lives inside one of those three.

Block 1: The Buried Loop

The underground heat collector is plastic pipe in a closed circuit, buried near the house. What flows through it is water, or water mixed with antifreeze. That is how the Plastics Pipe Institute, referencing the CSA/ANSI/IGSHPA C448 standard, describes the closed-loop heat-transfer fluid. (A "water or a mixture of water and antifreeze" phrasing circulates widely and gets attributed to DOE; it is not on DOE's current geothermal heat pump overview page or in its homeowner guide, so the standard is the better citation.)

Two things a diagram label should not claim about this pipe:

• A specific antifreeze. Which antifreeze chemistry and what concentration go in the loop depend on jurisdiction, equipment, pipe compatibility, and the design conditions. Nobody publishes a universal answer.
• A standard diameter. The PPI model specification sets material, certification, dimension-ratio and pressure-rating requirements for loop pipe, but it does not prescribe one residential diameter. Sizing is a project-by-project design output. So treat any diameter printed on a generic diagram as an illustration, not a specification.

What is published is the material: PPI recommends HDPE of grade PE4710, meeting C448 and NSF/ANSI 358-1, with heat-fused joints as the established conventional choice. PE-RT and PEX tubing are also covered by the model specification, with their own approved direct-burial mechanical fittings. The full parts list underground (pipe grades, fusion methods, flow-center valving, manifolds) is its own article: geothermal ground loop components.

The four shapes the loop takes

DOE's homeowner guide counts four loop types, in its own words: "these – horizontal, vertical, and pond/lake – are closed-loop systems. The fourth type of system is the open-loop option."

• Horizontal — pipe in trenches "at least four feet deep"; DOE calls this arrangement generally the most cost-effective where the land allows it.
• Vertical — pipe down drilled boreholes, "often used for larger-scale geothermal systems… or where the soil is too shallow to bury horizontal loops," and it "can be more expensive."
• Pond/lake — coils submerged "at least eight feet under the surface to prevent freezing," where the site has an adequate water body.
• Open loop — the fourth type, which draws and returns real groundwater instead of recirculating a sealed fluid.

A "slinky" loop, if your quote mentions one, is a coiled variant of the horizontal type, not a fifth category. Whichever shape the pipe takes, the closed-loop diagram is the same from the wall of the house inward; geometry changes the yard, not the cabinet.

The Line Where the Refrigerant Stops

Here is the boundary that makes or breaks the diagram.

So a correct diagram shows two closed circles that touch at one component. Circle one: buried pipe, loop fluid, circulation pump, and the water side of that exchanger. Circle two: the refrigerant loop, entirely inside the cabinet, running from the refrigerant side of that same exchanger through the compressor, air coil, and expansion device and back.

In direct geoexchange (DGX), refrigerant really does circulate through buried piping, which is exactly why ENERGY STAR classifies DGX as its own separate equipment category rather than a variant of the water-loop systems. One architecture earns the underground refrigerant lines. The conventional closed-loop system this page draws does not.

Block 2: Inside the Cabinet

The indoor unit is where a diagram gets crowded. The parts list below follows ClimateMaster's documentation for a packaged water-to-air unit, in the manufacturers' own terminology. ENERGY STAR sets efficiency criteria for this equipment class rather than a required component list, so read this as a representative build (a competing model may arrange or name things differently):

• Compressor — raises the refrigerant's pressure and temperature. It's also the main reason the electric meter spins; our guide to geothermal electricity usage covers what running it costs.
• Water-to-refrigerant heat exchanger (coaxial on this build) — the component where the two fluid circuits meet. Loop fluid on one side, refrigerant on the other.
• Refrigerant-to-air heat exchanger (air coil) — where the refrigerant trades heat with your house air. ENERGY STAR's term is the "indoor air heat exchange coil."
• Thermostatic expansion valve — drops the refrigerant's pressure and temperature so it can absorb heat again.
• Four-way reversing valve — the switch between heating and cooling. It redirects the refrigerant flow, which swaps which exchanger does which job.
• Blower — moves house air across the air coil and into the ducts. In a packaged unit it lives in this same cabinet.
• Service ports — the technician's access points to the refrigerant circuit.
• Safety controls — ClimateMaster's documentation names high- and low-pressure switches plus water-coil and air-coil temperature sensors watching the refrigerant circuit.

The refrigerant runs the classic cycle through those parts (evaporation, compression, condensation, expansion), and the cycle reverses for cooling. The physics of why compressing a gas lets you move heat uphill belongs to our companion piece on how geothermal heat pumps work, and how geothermal heating works traces the same path in heating mode from a homeowner's point of view. For the diagram, what matters is placement: all eight items above sit inside one cabinet, roughly where a furnace would stand, with two water lines entering from the loop side and a supply and return duct on the air side.

Block 3: The Distribution Subsystem

DOE's third block is the delivery network. For the water-to-air system drawn here, that means what it means for a furnace: return ducts bring house air to the cabinet, the blower pushes it across the air coil, and supply ducts carry the conditioned air to the registers.

Keep DOE's hedge in mind, though: ductwork is "generally used," not universal. A water-to-water system replaces this entire block with hydronic piping and emitters, and ENERGY STAR's phrase "air and/or hydronic space conditioning distribution system(s)" exists precisely because both are real. On a diagram, block 3 is whichever delivery network the house actually has, plus the temperature controls that tell the heat pump when to run.

The Flow Path in Heating Mode

Now trace the arrows. In heating mode, heat moves from the soil to your supply registers along this path:

1. Ground heat conducts through the buried pipe wall into the circulating water or water-antifreeze solution.
2. The circulation pump carries that fluid indoors to the water-to-refrigerant heat exchanger.
3. At that exchanger the loop fluid gives up its heat and returns to the ground loop. It stays inside its own sealed piping the whole way; it never enters the refrigerant circuit.
4. On the other side of the exchanger wall, the refrigerant absorbs that heat and evaporates. In heating mode this exchanger is acting as the evaporator.
5. The compressor raises the refrigerant vapor's pressure and temperature.
6. The reversing valve directs the hot vapor toward the indoor air coil.
7. At the air coil the refrigerant condenses, releasing its heat to the house air. The air coil is acting as the condenser.
8. The blower moves return air across the warm coil and out through the supply ducts to the registers.
9. The refrigerant passes through the expansion valve, dropping in pressure and temperature, and returns to the ground-side exchanger to collect more heat.

Two loops, one handoff, heat always moving toward the house. That's the whole heating diagram.

What Changes in Cooling Mode

On the simplified diagram, one change: the four-way reversing valve reverses the direction of refrigerant flow, swapping the roles of the two heat exchangers. (In the real machine, compressor staging, blower speed, expansion control and loop pumping can shift with mode and load too — a schematic just doesn't draw them.) The indoor air coil becomes the evaporator, absorbing heat from your house air; the ground-side exchanger becomes the condenser, rejecting that heat into the loop fluid, which carries it underground and sheds it to the soil.

What reverses is the refrigerant. Manufacturer and agency literature doesn't say whether the ground loop's pumping direction changes in cooling, and nothing in the operating principle requires it. The loop fluid does its job in either direction. So on the diagram, flip the refrigerant arrows and relabel the two exchangers; the water circuit and the two-fluid boundary stay exactly as drawn. What summer operation feels like, and how well it works, is covered in our guide to geothermal cooling.

Components on Some Diagrams, but Not All

Several parts show up on geothermal diagrams as if they were standard equipment. Per the manufacturers' own literature, they are options or configuration choices: real components, but only on some systems. If your quote includes one, it belongs on your diagram; if not, its absence is not a gap.

A diagram that draws every one of these as standard is drawing a maxed-out configuration, not a baseline system. Read yours against the quote in front of you.

Packaged Versus Split Systems

Everything above placed the machinery in one cabinet. That's the packaged (self-contained) layout: blower, compressor, ground-side heat exchanger, refrigerant-to-air coil, and controls all in a single box.

A split system redraws the indoor half. The compressor and ground-side section sit in one location, and refrigerant piping connects them to a remote air handler or A-coil-and-furnace combination with its blower somewhere else. Manufacturers name these two halves differently from one another, so read the equipment's own literature rather than assuming a diagram's labels carry across brands.

In a split system, refrigerant lines do run between two pieces of equipment: the two indoor sections. They still do not run underground. The boundary from earlier holds in both layouts: the ground loop carries loop fluid to a water-to-refrigerant heat exchanger, and the refrigerant stays on the equipment side of it.

Frequently Asked Questions

Does refrigerant flow through the buried ground loop?

Not in a conventional closed-loop system. The refrigerant circuit stays sealed inside the equipment, reaching the ground side only at a water-to-refrigerant heat exchanger; the buried loop circulates water or a water-antifreeze solution in its own sealed piping, in both heating and cooling. The exception is direct geoexchange (DGX), which does circulate refrigerant through buried piping, and which ENERGY STAR classifies as a separate equipment category for exactly that reason.

What size pipe does a geothermal ground loop use?

There is no single residential size. The PPI model specification governs the pipe's material, certification, dimension ratio and pressure rating, but leaves the diameter to the design. Pipe size comes out of your system's design, so treat any specific diameter as your designer's answer, not the industry's.

Does every geothermal system have a desuperheater?

No. ENERGY STAR's specification says water-to-air models may provide water heating through a desuperheater (partial heat recovery from the hot refrigerant gas leaving the compressor), and WaterFurnace lists its desuperheater coil as optional. It's a configuration choice to make at quote time, not a component your diagram gets by default.

Where does the reversing valve fit in the diagram?

Inside the refrigerant circuit, in the indoor cabinet, between the compressor and the two heat exchangers. It is the single four-way valve that reverses refrigerant flow to switch the system between heating and cooling, making the air coil and the ground-side exchanger trade evaporator and condenser roles. It never touches the water side.