Open Loop Geothermal and Well Water in Rural Oklahoma

I am Dave Hartzell. 47 years in HVAC, 15+ years running Hartzell’s Heat & Air out of Kingfisher, and I drill water wells as well as geothermal loops. So I get this call constantly: “I already have a well. Can I just run the geothermal off of it?”

Sometimes yes. Often no. Open loop is the decision where a bad yes shows up as a dead heat pump.

What open loop actually is

Open loop pulls water from the ground, runs it through the heat pump’s heat exchanger once, and sends it somewhere else. The trade calls it pump and dump. A standing column well draws from deep in the well and returns the water to the upper part of that same borehole; whether one fits is a site specific geology question I answer on site.

Closed loop is the opposite: the same fluid circulates through sealed pipe forever and the ground never has to produce a drop. The full comparison is on closed loop vs open loop geothermal.

Water quantity: the number one reason open loop fails

An open loop needs continuous water the whole time the compressor runs. The common design range is roughly 1.5 to 2 gallons per minute per ton, and the exact figure comes off the unit’s spec sheet.

A 4 ton system at 2 gallons per minute per ton wants 8 gallons per minute, continuously. On a July afternoon that compressor may run most of the day. Not sure what a ton is? Start with what a ton of geothermal means.

Here is the trap. A well that has served a house for twenty years is answering a different question. Household demand is intermittent peak: a shower, a load of laundry, a few minutes with hours to recover. A heat pump is sustained draw with no recovery. Fine for one is nowhere near enough for the other.

So I do not ask what your well puts out. I test sustained yield, pumping for hours and watching drawdown. I drill, case and develop wells myself, which is why I am willing to tell you no.

Water quality: the part that actually kills systems

Quantity gets the system installed. Quality decides whether it is still running in year five.

Open loop sends raw groundwater through the exchanger, so whatever is in the water goes through the machine:

• Iron and manganese. They oxidize and deposit on the exchanger wall, and feed iron bacteria whose slime is worse than the mineral.
• Hardness. Calcium and magnesium scale the transfer surface, and scale is an insulator: less heat moves, head pressure climbs, capacity falls.
• Sand and silt. Abrasive. They wear the inside of a coaxial exchanger and pack strainers.
• Hydrogen sulfide. The rotten egg smell. It attacks copper specifically, which is why cupronickel exchangers exist. If sulfide shows up, copper is off the table.
• Total dissolved solids. The catch all for everything else in solution, driving scaling and corrosion.

I will not publish chemistry limits on a web page. They belong to the unit’s water quality table and the lab report on your well, and I check one against the other.

This is where open loop quietly loses on cost. A fouled exchanger costs capacity first and money second: repeated cleanings, treatment nobody budgeted for, sometimes a replacement exchanger. Over ten years that can add up past the closed loop you skipped.

Where the water goes, which is the harder half

Everybody thinks about getting water out. The permit conversation is almost always about putting it back. The options are a return or injection well, a pond, or surface discharge.

I will not state a permit, a fee, or a statute on a web page, and you should be suspicious of a contractor who does. The discharge side is regulated, Oklahoma Water Resources Board rules and local rules both matter, and it is usually where an open loop project stalls. I check what applies to your address first.

One design point that is not paperwork: a return well set too close to the supply well short circuits thermally. The system drinks its own discharge and loses ground all season.

Pumping cost, the part nobody wants to talk about

An open loop moves water with a well pump. That electricity is a real operating cost, and it comes off the efficiency advantage you bought the system for.

A closed loop uses a small circulator, a fractional horsepower pump nudging fluid around a sealed circuit that is already full. An open loop uses a submersible pump lifting water against depth and pipe friction, and pumping power scales with lift.

The sticker rating does not account for your well pump’s full appetite, so what matters is the rating after the pump is paid for. On a deep well an open loop can deliver less real efficiency than the closed loop it beat on price. I run that against your well depth first.

Your neighbors are on the same aquifer

Rural Oklahoma wells share water. A heat pump pulling continuously is a bigger, steadier draw than a house, and it does not pause when the neighbor starts irrigating. Sustained pumping lowers the level in your own well, and on a tight aquifer it reaches the wells around you. It is a design input, not a courtesy issue.

What maintenance actually looks like

An open loop is not a closed loop with a well attached. It needs attention on a schedule your water sets:

• Heat exchanger cleaning. Mineral and biological fouling gets flushed out. How often depends on your chemistry. I set that interval after your lab results and the first year of operation.
• Filters, strainers and screens. They catch sand before the exchanger does, and they are the thing people forget.
• Flow and pressure checks. Falling flow is the early warning that fouling started.

Neglect runs a predictable path: flow drops, the exchanger fouls, head pressure climbs, the system trips on high pressure, and you are buying parts. More on geothermal system problems in Oklahoma.

When open loop is genuinely the right call

I am not against open loop. I am against open loop on the wrong well. It is strong when all of these line up:

• Strong, clean, tested water, sustained yield well above what the tonnage needs, and a lab report the equipment can live with.
• A real discharge path, workable where you are, not a hopeful one.
• Higher tonnage, where a closed field would have to get large and expensive.
• Land constraints: not enough open ground, rock, septic lines in the way, or a vertical bore field that prices out.

Then open loop can beat a closed field on cost and performance both. If not, read horizontal vs vertical vs pond loop first.

When I say no

I say it when sustained yield does not cover the tonnage with room left over. When the water test comes back with chemistry that will eat the exchanger. When there is no honest place for the discharge to go. When the water is deep enough that pumping cost erases the reason to do it.

That is not walking away from work. I would rather sell the closed loop and have you happy in year eight than argue in year three about a fouled exchanger I installed. When closed loop is the answer, here is how I install a geothermal system.

Questions I get from people with wells

How many gallons per minute does open loop geothermal need per ton?

Roughly 1.5 to 2 gallons per minute per ton, continuously, the whole time the compressor runs. A 4 ton system wants about 8 gallons per minute without a break. The exact figure comes off the unit’s spec sheet, confirmed by a yield test.

Can I use my existing house well for a geothermal heat pump in Oklahoma?

Maybe, and it has to be tested first. Household use is short peaks with hours to recover. A heat pump is sustained draw with no recovery. I test sustained yield by pumping for hours and watching drawdown.

How much does a geothermal diagnostic cost in Kingfisher Oklahoma?

$348 flat, any hour, weekday or after hours. That covers a full performance check with a written report and a quote before I leave. An estimate on a new system is free.