The Half-Hidden Cost of Year-Round Swimming
If you have a heated pool or spa in St. Johns, you already know the bill goes up when the temperature drops. What most homeowners don't know is that the maintenance routine shifts too, and ignoring those shifts is how heaters die after 3 years instead of 10.
Here's the honest care guide for heated pools and spas in Northeast Florida, including the months you're least likely to use them but most likely to wreck them.
Two Heater Types, Two Different Care Plans
Most heated St. Johns pools have one of two systems. They demand different things from you.
Gas heater (natural gas or propane)
The classic. Burns fuel to heat water as it passes through a copper or stainless heat exchanger. Heats fast (an hour from 70 to 88 in a typical 20,000 gallon pool). Expensive to run.
Failure mode: scale builds up inside the heat exchanger as calcium plates out on hot surfaces. After 3 to 5 years of bad water chemistry, the exchanger fails and you're looking at a $1,200 to $2,500 repair or a full replacement.
Heat pump
Uses electricity to extract heat from outdoor air and transfer it to the water. Slower (24 to 48 hours from cold start) but cheaper to run.
Failure mode: cold-weather damage. Heat pumps stop working efficiently below about 55 degrees outside. Most freeze damage in St. Johns happens to heat pumps left running during a cold snap when they shouldn't be.
If you don't know which kind you have, walk to the equipment pad. Gas heater is a big box with a vent stack and either gas line or propane tank nearby. Heat pump looks like a small AC unit with a top-mounted fan.
Chemistry Shifts Above 80 Degrees
Once your water is over 80 degrees, three things change.
Chlorine burns off faster. Higher temperature means higher oxidation rate. If your free chlorine was lasting a week at 75 degrees, it might last 3 days at 88. Test more often.
Calcium scales easier. Hot water holds less calcium in solution. The water deposits scale on tile, plaster, heat exchangers, and salt cells. Keep pH 7.4 to 7.6 strictly. Drop alkalinity if it's over 100.
pH climbs faster. Heated water outgasses CO2 quickly. CO2 in water is acidic, so as it escapes, pH rises. Heated pools often need acid additions twice a week.
The summary: if you're running the heater, test chemistry twice a week, not once.
Spa-Specific Issues
The attached spa is where most heated-pool damage actually happens.
Spas drain faster than they fill. A 600-gallon spa loses a noticeable percentage of volume in a single 30-minute soak through evaporation and splash-out. Refill regularly or the heater will run dry.
Spa chemistry runs harder. Higher temp, higher bather density, lower volume. A spa needs water replaced more often than a pool. Refresh the spa water every 60 to 90 days if it gets regular use.
Foam and sanitizer use. Hot, agitated water and skin oils create foam. Pool stores will sell you defoamer. Mostly it's a sign that bather load is high relative to chlorine. Increase chlorine to 4 to 5 ppm in heavy-use weeks.
Freeze Protection in St. Johns
We get 2 to 4 nights a year where temperatures drop below freezing. That's where most heater failures happen.
Run the pump continuously. Most pool automation systems have a "freeze protect" mode that kicks on the pump at 35 to 38 degrees. If you don't have automation, set the pump to run all night when the forecast is below 35.
Drain and shut down heat pumps. If a hard freeze (under 30 for 4+ hours) is coming, your heat pump should be drained. There's a drain plug on the bottom of the unit. Owner's manual has the location. Skipping this is how the coil splits and you replace a $4,000 heat pump.
Gas heaters mostly tolerate freeze. If the pump is running and water is moving, the gas heater is fine through a typical St. Johns cold snap. Issues happen when the gas valve sticks closed and the heater can't fire on demand. After a freeze, run the heater for 20 minutes to confirm it lights.
Spa cover stays on, but check it. A weighted spa cover keeps the heat in but if the spa fills with rain on top of the cover, water can pool, freeze, and crack the cover or the spa surround tile. Drain the top of the cover after rain.
When the Heater Stops Working
Common failures and rough diagnosis:
| Symptom | Likely cause | DIY or pro |
|---|---|---|
| Heater clicks but no flame (gas) | Gas valve, igniter, or pressure switch | Pro |
| Heater works but water never gets hot | Flow rate too low, blocked filter, undersized | Pro |
| Error code on display | Look up the code in the manual first | Sometimes DIY |
| Heat pump runs but air coming out is warm not cold | Refrigerant low, coil dirty | Pro |
| Pilot light won't stay lit | Thermocouple | DIY if you're comfortable |
| Loud rumbling noise inside heater | Scale buildup in heat exchanger | Pro, urgent — heater is dying |
The "loud rumble" symptom matters. It means scale is restricting flow inside the heater and the water in the exchanger is reaching boil temperature. That's the sound of an exchanger about to fail. Shut it off and call a pro that day.
The Annual Service That Saves You
If you have a heater, an annual service visit is worth the $150 to $250.
What a real service includes:
- Heat exchanger flush (descale with mild acid).
- Burner cleaning (gas) or coil cleaning (heat pump).
- Ignition system check.
- Gas pressure test (gas heaters).
- Refrigerant pressure check (heat pumps).
- Pump and flow verification.
- Calibration of any thermostat or controller.
Skipping this for 3 years adds up. Doing it annually extends heater life from a typical 5 to 7 years out to 10 to 15 in Florida conditions.
A Quick Reality Check on Cost
Running a heater in St. Johns isn't free:
- Gas heater: $250 to $500 a month if heated daily through November to March.
- Heat pump: $80 to $200 a month for the same period.
If you're not actually swimming, turn it off. The spa-only heating mode (some controllers have it) is cheaper than heating the whole pool.
Want a heater inspection before the next cold snap, or a real chemistry plan for a heated pool? Book a pool service in St. Johns, FL and we'll inspect the heater, pull a full chemistry panel, and put you on a service plan that protects the equipment year-round.
