Pool swim season in Plainfield, IL
When can you swim in an outdoor pool in Plainfield, IL?
An unheated pool in Plainfield never reaches 78°F in a normal year. It peaks around 76°F in Aug. The air allows up to 5 swimmable months with a heater (May to Sep).
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Heater options for a Plainfield pool, side by side
| 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 | $266 | $816 |
| Gas heater + cover | 5 | May to Sep | $307 | $732 |
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 Plainfield
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: Romeoville NWS Office, 7.4 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
Plainfield 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 | 32° | 24° | 1.7 | 25° | 31° | – | – |
| Feb | 36° | 28° | 2.6 | 26° | 32° | – | – |
| Mar | 49° | 39° | 3.6 | 34° | 40° | – | – |
| Apr | 61° | 50° | 4.7 | 46° | 52° | – | – |
| May | 72° | 61° | 5.5 | 58° | 64° | $183 | $205 |
| Jun | 82° | 71° | 6.1 | 69° | 75° | $48 | $61 |
| Jul | 85° | 75° | 6.2 | 76° | 82° | – | – |
| Aug | 83° | 73° | 5.4 | 76° | 82° | – | – |
| Sep | 76° | 66° | 4.5 | 71° | 77° | $35 | $41 |
| Oct | 64° | 54° | 3.0 | 60° | 66° | – | – |
| Nov | 49° | 40° | 2.0 | 46° | 52° | – | – |
| Dec | 37° | 29° | 1.5 | 33° | 39° | – | – |
Heating costs most in May (about $183 with a heat pump, $205 with gas). Sunshine peaks in Jul at 6.2 kWh/m²/day (NASA satellite data, 26.3 km grid cell). Highlighted months are swimmable with no heater.
How Plainfield compares with nearby cities
Plainfield ranks 117 of 225 Illinois cities for unheated swim months, and no nearby city gets a longer unheated season.
| City | Distance | Unheated months | Heat pump months | Heat pump $/yr |
|---|---|---|---|---|
| Romeoville, IL | 7 mi | 0 | 5 | $266 |
| Crest Hill, IL | 7 mi | 0 | 5 | $266 |
| Shorewood, IL | 7 mi | 0 | 5 | $297 |
| Oswego, IL | 7 mi | 0 | 5 | $288 |
| Bolingbrook, IL | 8 mi | 0 | 5 | $266 |
| Joliet, IL | 8 mi | 0 | 5 | $297 |