Pool swim season in Duluth, MN
Duluth, MN: how long the pool season really is
An unheated pool in Duluth never reaches 78°F in a normal year. It peaks around 69°F in Aug. The air allows up to 2 swimmable months with a heater (Jul to Aug).
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Heater options for a Duluth pool, side by side
| Option | Months | Swimmable | Energy/yr | All-in/yr |
|---|---|---|---|---|
| No heater | 0 | no month | $0 | $0 |
| Solar cover only | 0 | no month | $0 | $50 |
| Solar panels + cover | 2 | Jul to Aug | $0 | $283 |
| Heat pump + cover | 2 | Jul to Aug | $129 | $679 |
| Gas heater + cover | 2 | Jul to Aug | $177 | $602 |
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 Duluth
Solar panels + cover: 2 of 2 possible months for about $283 a year all-in, which works out near $142 for each month it adds.
A solar cover alone adds no swim months here, so if you want a longer season you need a heater (why); still use one at night to hold the heat you pay for. 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: Duluth Harbor Station, 2.1 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
Duluth 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 | 21° | 13° | 1.6 | 15° | 21° | – | – |
| Feb | 26° | 17° | 2.7 | 15° | 21° | – | – |
| Mar | 35° | 27° | 3.8 | 23° | 29° | – | – |
| Apr | 45° | 38° | 4.7 | 34° | 40° | – | – |
| May | 56° | 48° | 5.4 | 46° | 52° | – | – |
| Jun | 66° | 58° | 5.9 | 56° | 62° | – | – |
| Jul | 75° | 66° | 6.2 | 65° | 71° | $82 | $112 |
| Aug | 74° | 67° | 5.2 | 69° | 75° | $47 | $65 |
| Sep | 66° | 59° | 3.8 | 64° | 70° | – | – |
| Oct | 52° | 45° | 2.4 | 51° | 57° | – | – |
| Nov | 39° | 32° | 1.5 | 37° | 43° | – | – |
| Dec | 27° | 20° | 1.1 | 24° | 30° | – | – |
Heating costs most in Jul (about $82 with a heat pump, $112 with gas). Sunshine peaks in Jul at 6.2 kWh/m²/day (NASA satellite data, 41.4 km grid cell). Highlighted months are swimmable with no heater.
How Duluth compares with nearby cities
Duluth ranks 99 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 |
|---|---|---|---|---|
| Hermantown, MN | 5 mi | 0 | 3 | $281 |
| Superior, WI | 6 mi | 0 | 2 | $142 |
| Cloquet, MN | 18 mi | 0 | 3 | $280 |
| Hibbing, MN | 57 mi | 0 | 3 | $363 |
| Grand Rapids, MN | 73 mi | 0 | 3 | $230 |
| North Branch, MN | 96 mi | 0 | 4 | $261 |