Pool swim season in Charleston, SC
Swim season in Charleston without a heater, and with one
An unheated pool in Charleston reaches 78°F in Jun to Sep, about 4 months a year. The air allows up to 7 swimmable months with a heater (Apr to Oct).
- J
- F
- M
- A
- M
- J
- J
- A
- S
- O
- N
- D
What each heater buys you in Charleston
| Option | Months | Swimmable | Energy/yr | All-in/yr |
|---|---|---|---|---|
| No heater | 4 | Jun to Sep | $0 | $0 |
| Solar cover only | 6 | May to Oct | $0 | $50 |
| Solar panels + cover | 7 | Apr to Oct | $0 | $283 |
| Heat pump + cover | 7 | Apr to Oct | $84 | $634 |
| Gas heater + cover | 7 | Apr to Oct | $182 | $607 |
For a 450 sq ft pool held at 80°F, at SC prices of 15.9¢/kWh electricity and $17/Mcf gas. All-in spreads the purchase over the equipment's life.
The cheapest way to the full season in Charleston
Solar cover only: 6 of 7 possible months for about $50 a year all-in, which works out near $25 for each month it adds.
Before you pay for any heater, buy a solar cover: on its own it adds 2 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: Dwtn Charleston, 4.6 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
Charleston 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 | 58° | 51° | 2.8 | 52° | 58° | – | – |
| Feb | 60° | 53° | 3.4 | 52° | 58° | – | – |
| Mar | 66° | 59° | 4.6 | 58° | 64° | – | – |
| Apr | 72° | 66° | 6.0 | 65° | 71° | $78 | $168 |
| May | 79° | 74° | 6.5 | 73° | 79° | $6 | $14 |
| Jun | 84° | 79° | 6.5 | 80° | 86° | – | – |
| Jul | 88° | 82° | 6.3 | 84° | 90° | – | – |
| Aug | 86° | 81° | 5.7 | 85° | 91° | – | – |
| Sep | 83° | 78° | 4.8 | 81° | 87° | – | – |
| Oct | 76° | 69° | 4.1 | 75° | 81° | – | – |
| Nov | 67° | 60° | 3.1 | 65° | 71° | – | – |
| Dec | 61° | 54° | 2.5 | 56° | 62° | – | – |
Heating costs most in Apr (about $78 with a heat pump, $168 with gas). Sunshine peaks in May at 6.5 kWh/m²/day (NASA satellite data, 57.4 km grid cell). Highlighted months are swimmable with no heater.
How Charleston compares with nearby cities
Charleston ranks 13 of 42 South Carolina cities for unheated swim months, and no nearby city gets a longer unheated season.
| City | Distance | Unheated months | Heat pump months | Heat pump $/yr |
|---|---|---|---|---|
| Mount Pleasant, SC | 6 mi | 4 | 7 | $124 |
| James Island, SC | 7 mi | 4 | 7 | $84 |
| Hanahan, SC | 7 mi | 4 | 8 | $257 |
| North Charleston, SC | 8 mi | 4 | 8 | $257 |
| Goose Creek, SC | 12 mi | 4 | 8 | $257 |
| Summerville, SC | 17 mi | 3 | 7 | $180 |