Pool swim season in Mount Vernon, IL

Mount Vernon, IL: how long the pool season really is

An unheated pool in Mount Vernon reaches 78°F in Jul to Aug, about 2 months a year. The air allows up to 5 swimmable months with a heater (May to Sep).

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2. F
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4. A
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11. N
12. D

Heater options for a Mount Vernon pool, side by side

For a 450 sq ft pool held at 80°F, at IL prices of 19.2¢/kWh electricity and $11/Mcf gas. All-in spreads the purchase over the equipment's life.

The cheapest way to the full season in Mount Vernon

Solar cover only: 4 of 5 possible months for about $50 a year all-in, which works out near $25 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: Mt Vernon 3 NE, 4.5 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.

Mount Vernon month by month: air, sun and pool water

Heating costs most in May (about $134 with a heat pump, $156 with gas). Sunshine peaks in Jun at 6.5 kWh/m²/day (NASA satellite data, 41.8 km grid cell). Highlighted months are swimmable with no heater.

How Mount Vernon compares with nearby cities

Mount Vernon ranks 26 of 225 Illinois cities for unheated swim months, and no nearby city gets a longer unheated season.