Pool swim season in Jacksonville, IL
When can you swim in an outdoor pool in Jacksonville, IL?
An unheated pool in Jacksonville never reaches 78°F in a normal year. It peaks around 78°F in Aug. The air allows up to 5 swimmable months with a heater (May to Sep).
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What each heater buys you in Jacksonville
| Option | Months | Swimmable | Energy/yr | All-in/yr |
|---|---|---|---|---|
| No heater | 0 | no month | $0 | $0 |
| Solar cover only | 3 | Jul to Sep | $0 | $50 |
| Solar panels + cover | 4 | Jun to Sep | $0 | $283 |
| Heat pump + cover | 5 | May to Sep | $188 | $738 |
| Gas heater + cover | 5 | May to Sep | $221 | $646 |
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 Jacksonville
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 3 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: Jacksonville 2, 1.1 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
Jacksonville 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 | 35° | 26° | 2.0 | 28° | 34° | – | – |
| Feb | 41° | 31° | 2.8 | 28° | 34° | – | – |
| Mar | 52° | 41° | 3.7 | 37° | 43° | – | – |
| Apr | 65° | 53° | 4.9 | 49° | 55° | – | – |
| May | 75° | 64° | 5.6 | 61° | 67° | $149 | $172 |
| Jun | 83° | 73° | 6.3 | 72° | 78° | $24 | $31 |
| Jul | 87° | 76° | 6.4 | 78° | 84° | – | – |
| Aug | 86° | 75° | 5.6 | 78° | 84° | – | – |
| Sep | 80° | 67° | 4.7 | 73° | 79° | $15 | $18 |
| Oct | 67° | 55° | 3.3 | 61° | 67° | – | – |
| Nov | 52° | 42° | 2.3 | 48° | 54° | – | – |
| Dec | 40° | 31° | 1.7 | 35° | 41° | – | – |
Heating costs most in May (about $149 with a heat pump, $172 with gas). Sunshine peaks in Jul at 6.4 kWh/m²/day (NASA satellite data, 34.3 km grid cell). Highlighted months are swimmable with no heater.
How Jacksonville compares with nearby cities
Jacksonville ranks 55 of 225 Illinois cities for unheated swim months; Godfrey nearby gets a longer season without a heater.
| City | Distance | Unheated months | Heat pump months | Heat pump $/yr |
|---|---|---|---|---|
| Chatham, IL | 29 mi | 0 | 5 | $202 |
| Springfield, IL | 32 mi | 0 | 5 | $202 |
| Taylorville, IL | 50 mi | 0 | 5 | $161 |
| Godfrey, IL | 54 mi | 2 | 5 | $124 |
| Lincoln, IL | 54 mi | 0 | 5 | $211 |
| Macomb, IL | 56 mi | 0 | 5 | $223 |