The ideal pool temperature depends on who’s in the water and what they’re doing. Every degree you add also shows up on the heating bill. Below: how to pick a setpoint for the pool and the spa, and how to hold it through a Brevard County winter.
What temperature should a pool be?
The answer spans 78°F to 86°F, depending on whether you swim laps or float. That range joins two official ones. The U.S. Department of Energy says pool water typically runs 78°F to 82°F. The same page notes that the American Red Cross recommends 78°F for competitive swimming. The CDC’s Model Aquatic Health Code calls 83°F to 86°F the most comfortable range for typical recreational use.
The code’s annex breaks that down by activity, in a table adapted from USA Swimming (MAHC Annex, Table 5.7.4.7):
| Who’s in the water | Water temperature |
|---|---|
| Lap swimming and swim team | 78–82°F |
| Children’s swim lessons | 82°F |
| Children’s water fitness | 83–86°F |
| Water aerobics | 84–88°F |
| Older adults, moderate to high intensity | 83–86°F |
| Older adults, low intensity | 86–88°F |
| Arthritis exercise | 84–90°F |
| Pregnancy | 78–84°F |
A pool serves everyone at once, so set it for whoever gets cold first. A lap swimmer can live with a few degrees more than they’d pick.
Kids and older swimmers want it warmer
The water that suits a lap swimmer can feel too cool for a small child or a grandparent. The Energy Department notes that 78°F may be too cool for young children and the elderly, who may need 80°F or higher. The MAHC table above puts children’s lessons at 82°F and low-intensity exercise for older adults at 86°F to 88°F.
Pregnancy runs the other way. The same table tops out at 84°F for pregnant swimmers and notes that warmer water can cause adverse effects.
A spa stops at 104°F
Never set a spa or hot tub above 104°F. The U.S. Consumer Product Safety Commission has warned since 1979 that hot tub water should never exceed 104°F. The Model Aquatic Health Code caps public spas at the same 104°F.
That 1979 CPSC release called 100°F safe for a healthy adult and suggested special caution with young children. It told pregnant women to stay at 100°F or below. It also warned that hot tub thermostats could be off by as much as four degrees. Check the water with an accurate thermometer before you get in, whatever the display says.
What each degree on the thermostat costs
Each degree you add to the setpoint raises heating energy by 10% to 30%. That’s the Energy Department’s range, and it notes the percentage runs higher in warm climates, because holding 78°F there costs relatively little.
The DOE’s gas-heating table shows the effect for Miami, the closest listed city to Brevard. Its example is a 1,000-square-foot outdoor pool with an 80% efficient gas heater, uncovered 8 hours a day. There, the four-degree step from 78°F to 82°F raised the yearly heating cost by about 69%.
To turn those percentages into dollars for your own heater, use the running-cost math in the pool heater cost guide. Which fuel costs less per degree is its own question, answered on gas vs heat pump pool heaters.
A cover at night protects the setpoint
Evaporation is the biggest way a heated pool loses heat, and a cover cuts it down. The DOE calls evaporation by far the largest source of energy loss from a pool. One BTU warms a pound of water one degree, but each pound of 80°F water that evaporates takes 1,048 BTU.
Evaporation also climbs with a warmer pool, more wind and drier air, according to the same page. So the higher your setpoint, the more an open pool gives up on a breezy night.
Covering the pool whenever nobody’s using it is the single most effective way to cut heating costs. The DOE puts the possible savings at 50% to 70%. For daytime swimmers, its routine is simple: cover off just before you swim, back on as soon as you’re done.
Holding a setpoint through a Brevard January
January nights are when a setpoint is hardest to hold, because the gap between water and air is widest. At Melbourne’s airport, NOAA’s 1991–2020 normals put January’s average low at 51.7°F and its average temperature at 61.7°F.
The same normals average 15 January nights with a low at or below 50°F, about half the month. December averages 10 such nights and February about 9 (NOAA’s variable definitions).
The Energy Department sizes a heater on the difference between the pool and the average air temperature. It counts cool nights and wind as extra load. An 84°F setpoint against a 61.7°F January average is a gap of about 22 degrees. Drop the setpoint to 80°F and the gap shrinks to about 18.
Heat pumps start to lose efficiency once the air drops below 50°F. Those are the nights to make sure the cover goes on.
How long a cold pool takes to warm back up is covered on gas vs heat pump pool heaters.
Thermostat habits that save heat
Turn the heater down, or off, when nobody will swim for several days. The DOE says this saves energy and money. It also calls it a myth that reheating the pool costs more than you saved by letting it cool.
A few more habits keep the setpoint honest:
- Pick a number and leave it. At 10% to 30% a degree, nudging it up one degree at a time adds up.
- Swim only at night? In warm, humid weather, the DOE says it may pay to uncover the pool by day.
- Judge the water with a thermometer in the pool, not by how the first step feels.
When the water won’t reach the setpoint
A heater that runs all night without reaching the number on the display is telling you something. Check three things first. Is the pump running? Is the heater set to pool, not spa? Is the setpoint actually above the water temperature?
If all three check out, something inside the heater needs a look. A pre-season pool heater tune-up, done before the first cold night, is the time to catch slow faults. The Maintenance Club covers two tune-ups a year on a 22-item gas checklist, for gas heaters.
Pool still stuck below the setpoint? Start with pool heater repair.
Sources
- U.S. Department of Energy, Energy Saver, “Managing Swimming Pool Temperature for Energy Efficiency” (archived January 1, 2026).
- U.S. Department of Energy, Energy Saver, “Gas Swimming Pool Heaters” (archived).
- U.S. Department of Energy, Energy Saver, “Heat Pump Swimming Pool Heaters” (archived).
- U.S. Department of Energy, Energy Saver, “Swimming Pool Covers” (archived).
- CDC, 2024 Annex to the Model Aquatic Health Code, 5th edition, section 5.7.4.7, pages 170–171.
- CDC, 2024 Model Aquatic Health Code, 5th edition, code language, section 4.12.1.7, page 114.
- U.S. Consumer Product Safety Commission, “CPSC Warns Of Hot Tub Temperatures”.
- NOAA NCEI, 1991–2020 monthly normals, Melbourne International Airport (USW00012838), and the monthly normals documentation.
