Pool swim season in Stillwater, MN
When can you swim in an outdoor pool in Stillwater, MN?
An unheated pool in Stillwater never reaches 78°F in a normal year. It peaks around 72°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 Stillwater
| 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 | $200 | $750 |
| Gas heater + cover | 4 | Jun to Sep | $267 | $692 |
For a 450 sq ft pool held at 80°F, at MN prices of 16.4¢/kWh electricity and $11/Mcf gas. All-in spreads the purchase over the equipment's life.
The cheapest way to the full season in Stillwater
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: Stillwater 2SW, 1.4 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
Stillwater 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 | 22° | 14° | 1.8 | 16° | 22° | – | – |
| Feb | 28° | 18° | 2.9 | 16° | 22° | – | – |
| Mar | 41° | 30° | 3.9 | 25° | 31° | – | – |
| Apr | 55° | 45° | 4.7 | 39° | 45° | – | – |
| May | 67° | 57° | 5.4 | 53° | 59° | – | – |
| Jun | 76° | 67° | 6.0 | 65° | 71° | $85 | $116 |
| Jul | 79° | 71° | 6.3 | 72° | 78° | $18 | $26 |
| Aug | 78° | 69° | 5.2 | 72° | 78° | $16 | $23 |
| Sep | 71° | 61° | 4.0 | 66° | 72° | $81 | $102 |
| Oct | 58° | 48° | 2.6 | 54° | 60° | – | – |
| Nov | 41° | 33° | 1.6 | 39° | 45° | – | – |
| Dec | 28° | 20° | 1.2 | 25° | 31° | – | – |
Heating costs most in Jun (about $85 with a heat pump, $116 with gas). Sunshine peaks in Jul at 6.3 kWh/m²/day (NASA satellite data, 55.5 km grid cell). Highlighted months are swimmable with no heater.
How Stillwater compares with nearby cities
Stillwater ranks 79 of 103 Minnesota cities for unheated swim months, and no nearby city gets a longer unheated season.
| City | Distance | Unheated months | Heat pump months | Heat pump $/yr |
|---|---|---|---|---|
| Lake Elmo, MN | 6 mi | 0 | 4 | $196 |
| Oakdale, MN | 8 mi | 0 | 4 | $141 |
| Hudson, WI | 8 mi | 0 | 5 | $285 |
| White Bear Lake, MN | 9 mi | 0 | 4 | $109 |
| North St. Paul, MN | 9 mi | 0 | 4 | $144 |
| Hugo, MN | 10 mi | 0 | 4 | $200 |