Atlantic Well Drilling is a certified vertical geothermal installer. We do ALL of the work outside your home or commercial property for you or subcontract with your HVAC or Mechanical Contractor who completes the interior installation of your system. Our work is timely, efficient and guaranteed.

Open Loop vs. Closed Loop

Open Loop vs. Closed Loop

“Open loop” and “closed loop” refers to the source. The source side is the location where the heat pump will be extracting or rejecting heat to. The load side is the home we’re trying to heat or cool. Let’s start by looking at the pros and cons for each geothermal source. Remember that efficiencies for ALL water source heat pumps exceed that of any other heating system today:

Open Loop Source (“pump & dump” or “once-through”):

Refers to running domestic well water through the system and discharging somewhere

Closed Loop Source (Horizontal pit or trench, vertical bore, horizontal bore):

Refers to circulating the fluid out through the ground and back through the heat pump in a continuous loop with high density PE pipe


  • Control over water / brine quality
  • No scaling or build-up concern
  • Less maintenance
  • Zero water usage from well
  • Zero Energy Consumption from well pump


  • Typically, higher initial install costs
  • Requires yard space
  • Lower entering water temperatures (heating)

From the list above, open loop systems have the benefit of consistent entering water temperature (EWT). Your well water temp doesn’t change much year-round. The output heating capacity of the system is dependent on the EWT. The unit is extracting heat from the entering water, so if the temp of that water is higher, it has more capacity to heat your home (and consequently, it will also operate more efficiently). Closed loop systems circulate the same freeze protected fluid (brine) forever. This brine is extracting heat from the earth and EWT’s can get down to 30 degrees in late winter. For example, let’s look at the spec book and examine the heating capacity and efficiency of a 4-Ton unit and assume it’s late winter:

EWT:50 degrees30 degrees
Heating Capacity:47,800 Btu/hr37,500 Btu/hr
Power: 3.22 KW2.97 KW
COP:4.35 3.71

The open loop system is providing 10,300 more BTU’s than the closed loop system due to the elevated EWT. Open loop system is 435% efficient vs. the closed loop operating at 371% efficient. The thing that’s missing is the well pump. The well pump runs 100% of the time that the heat pump is running (it turns off when the heat pump shuts down). A residential variable speed well pump will draw ~ 5 amps or more at lower flow rates. This equates to another 1.2 KW and takes the total COP down to 3.12. (or 312% eff). At this rate the closed loop system is more efficient with less operating costs. It’s the turtle that wins the race in this example.

Experience shows us both open and closed loop systems are great. We have learned that open loops require a little more attention in the weeks directly following install. It’s good to check a new system frequently. Inspect the flow meter to verify correct water flow. This is important in the spring when sprinkler systems come on. Sprinklers or other large water demand on the well, can reduce the water flow rate through your heat pump. Sprinkler system start-up can also send a large amount of sand or other sediment up the pipe. You’ll want to check the sediment trap at the unit location and clean when needed. Once dialed in the system typically runs good with simple filter changes every 3 months.

At the end of the day both systems are going to far exceed the efficiency of anything else you could install. Air-source heat pumps have come a long way. However, they’ll never achieve the efficiency of a geothermal system because it’s just too difficult to extract heat from air that’s.