Pool swim season in Marathon, FL
When can you swim in an outdoor pool in Marathon, FL?
An unheated pool in Marathon reaches 78°F in Apr to Nov, about 8 months a year. The air allows up to 12 swimmable months with a heater (all year).
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Heater options for a Marathon pool, side by side
| Option | Months | Swimmable | Energy/yr | All-in/yr |
|---|---|---|---|---|
| No heater | 8 | Apr to Nov | $0 | $0 |
| Solar cover only | 12 | all year | $0 | $50 |
| Solar panels + cover | 12 | all year | $0 | $283 |
| Heat pump + cover | 12 | all year | $24 | $574 |
| Gas heater + cover | 12 | all year | $84 | $509 |
For a 450 sq ft pool held at 80°F, at FL prices of 15.3¢/kWh electricity and $25/Mcf gas. All-in spreads the purchase over the equipment's life.
The cheapest way to the full season in Marathon
Solar cover only: 12 of 12 possible months for about $50 a year all-in, which works out near $13 for each month it adds.
Before you pay for any heater, buy a solar cover: on its own it adds 4 months here for about $50 a year (why a cover comes first). If you get quotes, ask for gas as well as a heat pump: once the purchase price is counted, gas comes out cheaper all-in here (heat pump or gas).
Weather station: Marathon Airport, 1.5 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
Marathon month by month: air, sun and pool water
| Month | Air high | Air avg | Sun kWh/m²/day | Water, unheated | Water, covered | Heat pump $ | Gas $ |
|---|---|---|---|---|---|---|---|
| Jan | 76° | 70° | 3.9 | 72° | 78° | $15 | $53 |
| Feb | 78° | 72° | 4.8 | 73° | 79° | $9 | $31 |
| Mar | 81° | 75° | 5.9 | 76° | 82° | – | – |
| Apr | 84° | 78° | 6.6 | 80° | 86° | – | – |
| May | 88° | 82° | 6.7 | 84° | 90° | – | – |
| Jun | 90° | 84° | 6.3 | 86° | 92° | – | – |
| Jul | 91° | 85° | 6.4 | 88° | 94° | – | – |
| Aug | 92° | 86° | 6.1 | 89° | 95° | – | – |
| Sep | 90° | 84° | 5.4 | 87° | 93° | – | – |
| Oct | 86° | 81° | 4.8 | 84° | 90° | – | – |
| Nov | 81° | 76° | 4.1 | 80° | 86° | – | – |
| Dec | 78° | 73° | 3.6 | 75° | 81° | – | – |
Heating costs most in Jan (about $15 with a heat pump, $53 with gas). Sunshine peaks in May at 6.7 kWh/m²/day (NASA satellite data, 54.5 km grid cell). Highlighted months are swimmable with no heater.
How Marathon compares with nearby cities
Marathon ranks 1 of 173 Florida cities for unheated swim months, and no nearby city gets a longer unheated season.
| City | Distance | Unheated months | Heat pump months | Heat pump $/yr |
|---|---|---|---|---|
| Key West, FL | 49 mi | 8 | 12 | $47 |
| Florida City, FL | 60 mi | 6 | 12 | $134 |
| Homestead, FL | 62 mi | 6 | 12 | $134 |
| Cutler Bay, FL | 73 mi | 6 | 12 | $162 |
| Palmetto Bay, FL | 76 mi | 7 | 12 | $47 |
| Pinecrest, FL | 79 mi | 7 | 12 | $47 |