Geothermal Heat Pump Installation: What Actually Happens

A geothermal heat pump installation is several projects wearing one contract. A drilling or excavation crew builds a heat exchanger into your yard. An HVAC crew sets and connects equipment inside the house. Then, before the unit is ever powered on, somebody has to verify that everything both crews did actually holds. And the sequence tying it all together is published nowhere — no federal agency or standards body issues a stage list for a residential install.

This guide walks a closed-loop, water-to-air retrofit of a single-family home stage by stage: what happens, in what order, who does it, and what to check before you hand over the final payment. For what it costs, see the geothermal installation cost guide; for how long it takes, the installation timeline article. This page is about the work itself.

The System This Guide Covers

"Geothermal installation" covers a lot of different projects, and they don't all follow the same steps. This guide describes one specific residential scenario: a closed-loop, water-to-air system retrofitted into an existing single-family home — buried pipe circulating fluid in a sealed loop, a heat pump indoors, and conditioned air delivered through ductwork.

That scope matters, because the process genuinely differs outside it:

• Open-loop systems pump groundwater instead of circulating sealed fluid, which pulls well construction and water-discharge rules into the picture that closed loops avoid.
• Water-to-water and hydronic systems replace the ductwork side with radiant floors or fan coils — a different indoor installation entirely.
• Pond loops trade drilling and trenching for lake work.
• New construction folds the loop field into site work before there's a lawn to dig up; commercial projects run at a different scale with different engineering.

The U.S. Department of Energy describes a geothermal heat pump system as three functional pieces: the underground heat collector, the heat pump itself, and the heat-distribution subsystem — generally conventional ductwork. ENERGY STAR's equipment definition is more specific about the heat pump unit itself: factory-made assemblies containing "indoor conditioning and/or domestic water heat exchanger(s), compressors, and a ground-side heat exchanger," with the overall system including the ground heat exchanger, air and/or hydronic distribution, temperature controls, and possibly thermal-storage tanks.

Keep those three pieces in mind — collector, heat pump, distribution — they are a useful way to organize everything that follows.

If you haven't yet confirmed your lot can host a loop field at all, start with whether your property is suitable for geothermal before worrying about process.

The Stage Sequence — and Why There Is No Official One

If you search this topic, you'll find tidy numbered graphics: "1. Consultation, 2. Design, 3. Installation, 4. Enjoy!" What those graphics leave out: no federal agency or standards body publishes a complete, residential-only stage taxonomy that starts at "signed contract." They are marketing sequences, not documented process.

There is no partial exception to that, either — no DOE document publishes a stage sequence for a house. What DOE does publish is a description of the system's functional parts, in its own words:

"An underground heat collector — A geothermal heat pump uses the earth as a heat source and sink (thermal storage), using a series of connected pipes buried in the ground near a building."

"A heat distribution subsystem — Conventional ductwork is generally used to distribute heated or cooled air from the geothermal heat pump throughout the building."

— U.S. Department of Energy, "What is in a Geothermal Heat Pump System?"

Between those two sits the heat pump itself. Note DOE's word "generally" in the ductwork sentence — it draws the same boundary this guide's scope section does: ducted air distribution is the arrangement DOE treats as the general one, not the only one.

So the sequence below is not a published standard, because none exists. It is a practical ordering for this guide's configuration, assembled from what is documented at each individual stage. Permitting, ground work, indoor work, and commissioning can overlap or be sequenced differently by project, though some dependencies hold regardless — you cannot commission a loop that isn't in the ground yet:

1. Design — a heating-and-cooling load calculation, then equipment and loop selection sized to it
2. Permitting — which varies enormously by location and loop type (more below)
3. Ground-loop installation — the "underground heat collector"
4. Indoor installation — the heat pump and the distribution side
5. Flush, fill, purge, test, and start up — the stage backed by a manufacturer-published checklist
6. Owner handoff

The gap extends inside the stages, too. What happens between contract signing and final design — the site survey, the utility locates, the final loop layout — is standard industry practice, and no authoritative source documents it. Documented requirements and common practice are different kinds of claims, and they appear here marked as what each one is.

Stage 1: Load Calculation and Design

Everything downstream — loop size, bore or trench count, equipment capacity, operating cost — hangs on one engineering step: a heating-and-cooling load calculation for your specific house. Sizing follows the load calculation; the load calculation does not follow a rule of thumb.

This is the stage where the design decisions get made:

• Loop configuration. Vertical bores or horizontal trenches, driven by your lot size, geology, and access. The trade-offs get a full treatment in horizontal vs. vertical ground loops.
• Equipment selection. The heat pump unit itself — what ENERGY STAR describes as one or more factory-made assemblies — matched to the calculated load, plus controls and any water-heating or thermal-storage components.
• Distribution. In a water-to-air retrofit, this usually means evaluating your existing ductwork and deciding what, if anything, needs modification.

What should you verify at this stage? That a load calculation actually happened. If a contractor quotes you a bore depth, a pipe length, or an equipment size before running one, they are quoting from habit, not from your house. The section on unpublished numbers below explains why that matters more in geothermal than in ordinary HVAC.

Stage 2: Permits

Here is the fact that shapes this whole stage: there is no national residential geothermal permit sequence. Permitting is a mix of state, county, and municipal requirements, and which of them apply to you depends on where you live, what loop type you're installing, and in some places, how deep you're going.

Four real jurisdictions, four different rules — and, more usefully, four different variables the rules turn on:

Notice that these four don't even key on the same variable. Iowa cares about depth. North Carolina cares about loop type — and under its program, an open-loop system needs a permit while a horizontal closed loop doesn't. Michigan routes through local health departments plus erosion rules tied to acreage and water proximity. Fairfax County treats it as ordinary mechanical permitting. A rule that decides your neighbor's project in one state may not exist at all in the next.

Across jurisdictions, the permits that show up include mechanical, electrical, building, well/bore, groundwater discharge, and erosion control — a composite drawn from these four examples, not a national requirement. Your project will need some subset of it, depending on where you live and what loop type you use.

What to verify at this stage: ask your contractor to name the specific permits your project needs, from the specific bodies that issue them, and to tell you who is pulling each one. A contractor who works your area regularly should be able to name them; if they can't, that is worth noticing. For a deeper treatment of how this varies, see geothermal permits and regulations.

Stage 3: The Ground Loop

This stage puts heavy equipment and real site disturbance in your yard — a rig or an excavator, building what DOE calls the "underground heat collector." What the work looks like depends on which configuration your design settled on.

Vertical bores

A vertical closed-loop project may include these steps — exact requirements and sequencing depend on the design, the installer, the equipment manufacturer, and your jurisdiction: a rig drills boreholes, the crew installs continuous HDPE loop piping down each bore, connects the bores to header piping running to the building, grouts the borehole, and then the assembled loop is pressure-tested, flushed, filled, and purged before startup.

Grouting is buried the day it's done and difficult to correct afterward. It seals the space around the loop pipe so the borehole doesn't become a channel between groundwater layers. North Carolina's Department of Environmental Quality states the requirement in its jurisdiction plainly: closed-loop geothermal boreholes "must be grouted the entire length of the borehole." That is one state's rule, not a national code — but it's a clear illustration of why regulators care about this step, and full-length grouting is a reasonable thing to ask any driller whether they do and how they verify it.

The drilling operation itself — rigs, mud, spoils, what your yard looks like during and after — gets its own article: geothermal drilling and wells.

Horizontal trenches

The horizontal sequence: an excavator digs parallel trenches, the crew lays continuous HDPE piping — either conventional multi-pipe runs or the compact coiled configuration called a "slinky" — runs header piping to the house, then backfills and restores the surface.

DOE publishes one loop-geometry figure for this work: horizontal systems use "trenches at least four feet deep." Depth matters because the pipe needs to sit below the soil layer that swings with the seasons. How much total trench and pipe your system needs, though, is a design output — see the unpublished-numbers section for why nobody can hand you that figure off a chart.

What to verify at this stage

For either configuration, the checkable claims are: the loop is continuous HDPE, the headers are connected and routed to the house, boreholes are grouted (and to what length), and — critically — the loop was pressure-tested, flushed, filled, and purged before anyone calls it done. Those last steps reappear on the manufacturer's startup checklist below, which is your lever for confirming they happened. For what each piece of the buried assembly actually is, see ground loop components explained.

Stage 4: Indoor Installation

From here on, the project looks much more like conventional HVAC work. The heat pump unit is set (typically where your furnace or air handler lives now), connected on three fronts:

• To the ground loop, via the header piping that entered the house in stage 3
• To your ductwork — the "heat-distribution subsystem," which DOE notes is generally conventional ductwork in a system like this
• To power and controls — line-voltage electrical, low-voltage control wiring, thermostat, and a condensate drain, since the unit dehumidifies in cooling mode just as an air conditioner does

Under ENERGY STAR's definition, a geothermal heat pump model normally consists of one or more factory-made assemblies containing the heat exchangers, compressor, and ground-side heat exchanger.

The verification tool for this stage lives in the next section: every connection made here — power sizing, low-voltage wiring, piping, condensate, blower, filter — appears as a line item on WaterFurnace's startup checklist, which is that manufacturer's document for its own equipment. The indoor work is verified at commissioning.

Stage 5: Startup and Commissioning

Commissioning is the stage for which a manufacturer publishes an itemized checklist — documentation specific enough that you can use it yourself.

WaterFurnace, a U.S. geothermal equipment manufacturer, publishes an installation guide (document IGV5-0006WA, dated 10/25) whose startup section opens with a hard gate. Before the unit is powered on, the guide directs the installer to check the following:

The same document adds: "NOTE: Complete the Equipment Start-Up/Commissioning Check Sheet during this procedure." In other words, the manufacturer expects a written commissioning record to exist for your installation.

It is one manufacturer's checklist from one document, not an industry standard or a code requirement. If your system is a different brand, your unit's installation guide will have its own startup procedure. But as evidence of what commissioning is — a specific, itemized set of conditions that must be true before the system is energized — it gives you something concrete to hold in your hands and ask about.

How to use it

Read the list again as a homeowner rather than a technician. "Water system cleaned and flushed" and "air is purged from closed loop system" verify the loop work from stage 3. Power sizing, low-voltage wiring, condensate pitch, and blower rotation verify the indoor work from stage 4. Every earlier stage surfaces here as a checkable line.

So use it:

1. Ask your installer whether they complete a written startup/commissioning checklist, and ask for a copy of it. For a WaterFurnace unit, that's the Equipment Start-Up/Commissioning Check Sheet the manufacturer's own guide directs them to complete. For other brands, ask what their equivalent is.
2. Ask them to walk you through it — particularly the flush and purge items, because trapped air and construction debris in the loop are invisible to you and consequential to the system.
3. Keep the completed sheet with your paperwork. It documents the as-commissioned state of the system, which matters for service calls and warranty questions later.

That's the whole play: get the record, understand it, keep it.

Stage 6: Owner Handoff

The last documented step is small but real: WaterFurnace's guide requires the installer to give the manual to the owner. Before the crew leaves for the last time, you should be holding three things — the equipment manual, the completed commissioning check sheet, and your permit and inspection records.

Who Does the Work — and Who Requires It

A residential geothermal retrofit typically involves a drilling or excavation crew for the loop field and an HVAC contractor for the indoor work and startup — sometimes one company, sometimes a contractor subcontracting the ground work.

The requirement to use qualified people comes from a specific place. WaterFurnace's installation guide states: "Only trained and qualified service personnel should install, repair or service heating and air conditioning equipment." That is a manufacturer's instruction — not a federal rule. There is no universal federal requirement that a residential geothermal system be installed by a certified geothermal installer; check your own equipment's warranty terms for what they require of the installation, alongside whatever contractor licensing your state imposes on HVAC, electrical, and well-drilling work.

The practical consequence: warranty terms come from the manufacturer, so its installation requirements are the ones that matter for coverage — verify your installer meets them.

The Numbers Nobody Publishes

Competing installation guides state numbers with great confidence at exactly the points where no authoritative source publishes one. Three examples, each a question your contractor should answer from your load calculation rather than from a chart:

Vertical bore depth. No authoritative source publishes a standard residential bore depth. DOE has published a case study of a system with 60 vertical wells "around 90 feet deep" — but that is a demonstration building at a county extension office, not a residential design rule, and generalizing it to your house would be exactly the error this section is warning about. Your bore depth and bore count come out of the load calculation and the geology under your lot.

Horizontal pipe length. No universal residential pipe-length figure is published; how much pipe your system needs is design-dependent, coming out of the load calculation. (DOE's figure — trenches at least four feet deep — is about depth, not length.)

Borehole and trench spacing. Spacing figures circulate in industry FAQs, but no federal or standards body publishes residential spacing rules in openly checkable form, so no spacing numbers appear in this article.

The takeaway isn't that these quantities are unknowable — your system will have an exact bore depth and pipe length, calculated for your house. The takeaway is that a contractor quoting bore depth or pipe length before running a load calculation is guessing, and a published-sounding number in a sales pitch deserves the question: calculated from what?