Pool swim season in Spearfish, SD
Swim season in Spearfish without a heater, and with one
An unheated pool in Spearfish never reaches 78°F in a normal year. It peaks around 73°F in Aug. The air allows up to 4 swimmable months with a heater (Jun to Sep).
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What each heater buys you in Spearfish
| Option | Months | Swimmable | Energy/yr | All-in/yr |
|---|---|---|---|---|
| No heater | 0 | no month | $0 | $0 |
| Solar cover only | 1 | Aug | $0 | $50 |
| Solar panels + cover | 4 | Jun to Sep | $0 | $283 |
| Heat pump + cover | 4 | Jun to Sep | $198 | $748 |
| Gas heater + cover | 4 | Jun to Sep | $265 | $690 |
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 Spearfish
Solar panels + cover: 4 of 4 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 1 month 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: Spearfish, 2.8 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
Spearfish 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 | 36° | 26° | 1.9 | 26° | 32° | – | – |
| Feb | 37° | 27° | 2.9 | 26° | 32° | – | – |
| Mar | 46° | 35° | 4.0 | 32° | 38° | – | – |
| Apr | 55° | 44° | 5.0 | 41° | 47° | – | – |
| May | 64° | 53° | 5.9 | 51° | 57° | – | – |
| Jun | 75° | 63° | 6.8 | 62° | 68° | $103 | $137 |
| Jul | 84° | 71° | 7.0 | 71° | 77° | $24 | $35 |
| Aug | 83° | 70° | 6.0 | 73° | 79° | $7 | $11 |
| Sep | 74° | 61° | 4.7 | 67° | 73° | $64 | $82 |
| Oct | 58° | 47° | 3.1 | 54° | 60° | – | – |
| Nov | 46° | 36° | 2.1 | 40° | 46° | – | – |
| Dec | 37° | 27° | 1.6 | 30° | 36° | – | – |
Heating costs most in Jun (about $103 with a heat pump, $137 with gas). Sunshine peaks in Jul at 7.0 kWh/m²/day (NASA satellite data, 25.1 km grid cell). Highlighted months are swimmable with no heater.
How Spearfish compares with nearby cities
Spearfish ranks 11 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 |
|---|---|---|---|---|
| Rapid City, SD | 41 mi | 0 | 4 | $136 |
| Box Elder, SD | 45 mi | 0 | 4 | $160 |
| Gillette, WY | 84 mi | 0 | 4 | $166 |
| Sheridan, WY | 156 mi | 0 | 4 | $216 |
| Casper, WY | 169 mi | 0 | 4 | $151 |
| Pierre, SD | 173 mi | 0 | 4 | $99 |