Pool swim season in Washington, IL
Swim season in Washington without a heater, and with one
An unheated pool in Washington never reaches 78°F in a normal year. It peaks around 77°F in Jul. The air allows up to 5 swimmable months with a heater (May to Sep).
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Heater options for a Washington 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 | $218 | $768 |
| Gas heater + cover | 5 | May to Sep | $254 | $679 |
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 Washington
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: Congerville 2NW, 11.7 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
Washington 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 | 33° | 25° | 1.9 | 27° | 33° | – | – |
| Feb | 38° | 29° | 2.8 | 27° | 33° | – | – |
| Mar | 50° | 41° | 3.7 | 36° | 42° | – | – |
| Apr | 63° | 52° | 4.9 | 48° | 54° | – | – |
| May | 74° | 63° | 5.6 | 60° | 66° | $161 | $183 |
| Jun | 83° | 72° | 6.3 | 71° | 77° | $34 | $44 |
| Jul | 86° | 75° | 6.4 | 77° | 83° | – | – |
| Aug | 84° | 73° | 5.6 | 77° | 83° | – | – |
| Sep | 80° | 67° | 4.7 | 72° | 78° | $23 | $27 |
| Oct | 67° | 55° | 3.2 | 61° | 67° | – | – |
| Nov | 51° | 42° | 2.2 | 47° | 53° | – | – |
| Dec | 39° | 31° | 1.6 | 35° | 41° | – | – |
Heating costs most in May (about $161 with a heat pump, $183 with gas). Sunshine peaks in Jul at 6.4 kWh/m²/day (NASA satellite data, 23.6 km grid cell). Highlighted months are swimmable with no heater.
How Washington compares with nearby cities
Washington ranks 76 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 |
|---|---|---|---|---|
| East Peoria, IL | 6 mi | 0 | 5 | $190 |
| Morton, IL | 7 mi | 0 | 5 | $218 |
| Peoria, IL | 10 mi | 0 | 5 | $190 |
| Pekin, IL | 14 mi | 0 | 5 | $190 |
| Normal, IL | 26 mi | 0 | 5 | $254 |
| Bloomington, IL | 29 mi | 0 | 5 | $254 |