Pool swim season in Marshall, MN
When can you swim in an outdoor pool in Marshall, MN?
An unheated pool in Marshall never reaches 78°F in a normal year. It peaks around 75°F in Jul. The air allows up to 5 swimmable months with a heater (May to Sep).
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What each heater buys you in Marshall
| 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 | $340 | $890 |
| Gas heater + cover | 5 | May to Sep | $431 | $856 |
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 Marshall
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: Marshall, 1.6 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
Marshall 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 | 25° | 14° | 2.0 | 16° | 22° | – | – |
| Feb | 29° | 18° | 3.0 | 16° | 22° | – | – |
| Mar | 41° | 30° | 3.9 | 25° | 31° | – | – |
| Apr | 57° | 45° | 4.8 | 39° | 45° | – | – |
| May | 70° | 58° | 5.5 | 54° | 60° | $211 | $257 |
| Jun | 81° | 69° | 6.2 | 67° | 73° | $66 | $93 |
| Jul | 85° | 73° | 6.6 | 75° | 81° | – | – |
| Aug | 82° | 70° | 5.5 | 74° | 80° | – | – |
| Sep | 75° | 62° | 4.2 | 68° | 74° | $63 | $81 |
| Oct | 60° | 48° | 2.8 | 55° | 61° | – | – |
| Nov | 43° | 33° | 1.9 | 39° | 45° | – | – |
| Dec | 30° | 20° | 1.4 | 25° | 31° | – | – |
Heating costs most in May (about $211 with a heat pump, $257 with gas). Sunshine peaks in Jul at 6.6 kWh/m²/day (NASA satellite data, 23.6 km grid cell). Highlighted months are swimmable with no heater.
How Marshall compares with nearby cities
Marshall ranks 24 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 |
|---|---|---|---|---|
| Brookings, SD | 50 mi | 0 | 4 | $183 |
| Worthington, MN | 57 mi | 0 | 4 | $174 |
| Willmar, MN | 59 mi | 0 | 4 | $170 |
| New Ulm, MN | 66 mi | 0 | 4 | $134 |
| Brandon, SD | 71 mi | 0 | 5 | $255 |
| Watertown, SD | 74 mi | 0 | 4 | $182 |