Pool swim season in Vermillion, SD
When can you swim in an outdoor pool in Vermillion, SD?
An unheated pool in Vermillion never reaches 78°F in a normal year. It peaks around 76°F in Jul. The air allows up to 5 swimmable months with a heater (May to Sep).
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Heater options for a Vermillion pool, side by side
| Option | Months | Swimmable | Energy/yr | All-in/yr |
|---|---|---|---|---|
| No heater | 0 | no month | $0 | $0 |
| Solar cover only | 2 | Jul to Aug | $0 | $50 |
| Solar panels + cover | 4 | Jun to Sep | $0 | $283 |
| Heat pump + cover | 5 | May to Sep | $222 | $772 |
| Gas heater + cover | 5 | May to Sep | $294 | $719 |
For a 450 sq ft pool held at 80°F, at SD prices of 14.6¢/kWh electricity and $10/Mcf gas. All-in spreads the purchase over the equipment's life.
The cheapest way to the full season in Vermillion
Solar panels + cover: 4 of 5 possible months for about $283 a year all-in, which works out near $71 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: Vermillion 2 SE, 1.4 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
Vermillion 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 | 31° | 20° | 2.0 | 21° | 27° | – | – |
| Feb | 36° | 25° | 3.1 | 23° | 29° | – | – |
| Mar | 48° | 37° | 3.8 | 32° | 38° | – | – |
| Apr | 62° | 49° | 5.0 | 45° | 51° | – | – |
| May | 73° | 60° | 5.8 | 57° | 63° | $149 | $190 |
| Jun | 82° | 71° | 6.5 | 69° | 75° | $39 | $57 |
| Jul | 86° | 74° | 6.6 | 76° | 82° | – | – |
| Aug | 83° | 72° | 5.6 | 76° | 82° | – | – |
| Sep | 78° | 65° | 4.5 | 70° | 76° | $34 | $47 |
| Oct | 65° | 52° | 3.2 | 58° | 64° | – | – |
| Nov | 48° | 37° | 2.2 | 43° | 49° | – | – |
| Dec | 34° | 24° | 1.6 | 29° | 35° | – | – |
Heating costs most in May (about $149 with a heat pump, $190 with gas). Sunshine peaks in Jul at 6.6 kWh/m²/day (NASA satellite data, 46.8 km grid cell). Highlighted months are swimmable with no heater.
How Vermillion compares with nearby cities
Vermillion ranks 4 of 14 South Dakota cities for unheated swim months, and no nearby city gets a longer unheated season.
| City | Distance | Unheated months | Heat pump months | Heat pump $/yr |
|---|---|---|---|---|
| Yankton, SD | 25 mi | 0 | 5 | $228 |
| Sioux City, IA | 34 mi | 0 | 5 | $245 |
| South Sioux City, NE | 34 mi | 0 | 5 | $218 |
| Le Mars, IA | 38 mi | 0 | 5 | $263 |
| Harrisburg, SD | 46 mi | 0 | 4 | $119 |
| Sioux Falls, SD | 53 mi | 0 | 4 | $93 |