On a 92-degree day with a 76 dew point, the ground under St. Augustine is still about 70: the geothermal case
Every air-source system in town fights the August air. A geothermal system ignores it and trades heat with the ground instead, which has not noticed it is summer.
August at the condenser versus August six feet down
Stand next to an outdoor unit on a Marsh Creek patio at four in the afternoon in August. The air is 92 degrees, the dew point is 76, and the unit is trying to dump heat into air that is already nearly as hot as the coil. That is the hardest job in residential cooling, and every air-source system in St. Augustine does it all summer.
Six feet below the same patio, the ground is in the low 70s. It was in the low 70s in January, too. A geothermal heat pump moves heat into that stable ground in summer and pulls it back out in winter, which is why its efficiency numbers look like a misprint next to an air-source unit’s.
Five things people believe about geothermal here
- It is a cold-climate product and makes no sense in Florida.
- You need acres of land for the loop.
- The high water table under St. Johns County ruins it.
- It cannot handle Florida humidity.
- Sand does not conduct heat, so the loop will not work.
Each one is backwards or half-wrong, and the half-wrong ones are the interesting part.
What is true instead
Geothermal pays off wherever the gap between air temperature and ground temperature is large, and a St. Augustine August qualifies as well as a northern January does. A vertical loop needs a drill rig and a small patch of yard, not acres; horizontal loops are the land-hungry kind. The water table, far from ruining the loop, improves it: wet sand conducts heat far better than dry sand, and most of the county’s soil is wet sand. A geothermal unit with a variable-speed blower runs long, slow cycles that wring water out of the air exactly the way the best air-source systems do. And with no outdoor unit, there is nothing on the patio to corrode in salt air, nothing to shut down in a hurricane, and nothing to hear.
What is honestly true on the other side: the upfront cost is higher than an air-source system, the loop is permanent and has to be designed right the first time, and the payback runs in years, not months. The federal tax credit that once shortened it ended for systems placed in service after 2025; FPL’s residential program may still apply to the heat pump side. Ask about current rebate eligibility for geothermal installs. [[CONFIRM WITH JERRY]]
Ask whether your lot qualifies
Where it makes sense around St. Augustine
- Acreage in Flagler Estates, Hastings and Elkton. Room for the loop, a closed system that leaves the sulfur well alone, and owners who plan to stay. The best fit in the market.
- Larger lots in Palencia and World Golf Village. Vertical bores on a new build or a full system replacement, usually for an owner who wants the quietest, longest-lived system available.
- The beach and bayfront. For the corrosion reason above, if the lot allows a bore.
- Not downtown. Lots in the Colonial Quarter and Lincolnville are small, the ground is archaeologically sensitive, and preservation review complicates any excavation. Ductless heat pumps are the right answer there.
- Not condos. No ground, no loop.
What we check before saying yes
Soil and access for the rig, the lot’s drainage, electrical capacity at the panel, the condition of the ductwork the unit will feed, and whether the owner’s time horizon fits a system whose economics are measured over a decade. We do say no when it doesn’t fit, and we say it before the drill rig is scheduled.
Geothermal questions from St. Johns County property owners
Can a loop field go under a Davis Shores lot that floods?
Technically a loop does not mind water; the equipment inside the house does. On a lot that takes king-tide flooding a dozen times a year, the indoor unit has to be elevated like any other air handler, and the small lots there make vertical loops the only option. It is possible, but it is rarely the lot we would pick for it.
Does geothermal get rid of the outdoor unit that keeps rusting at Crescent Beach?
Yes. That is one of its quietest advantages on the coast: there is no condenser outside at all, so nothing for salt spray to eat and nothing to tie down before a storm. The whole system lives indoors and underground.
Our Flagler Estates well has sulfur. Does that rule out an open-loop system?
It rules out the open-loop kind, which runs well water through the unit, because sulfur and iron foul the heat exchanger. A closed loop uses sealed pipe and its own fluid, never touches the well, and is what we would quote there.
How much of the yard gets torn up on a half-acre lot?
For vertical bores, a drill rig works a small area and the trenches to the house are narrow; the lawn recovers in a season. Horizontal loops need more open ground and are only practical on larger acreage toward Hastings and Elkton.
Have the lot for it?
We install geothermal and solar-compatible systems. Free estimates, including the honest no.