Pool swim season in Union, MO
Union, MO: how long the pool season really is
An unheated pool in Union reaches 78°F in Jul to Aug, about 2 months a year. The air allows up to 7 swimmable months with a heater (Apr to Oct).
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What each heater buys you in Union
| Option | Months | Swimmable | Energy/yr | All-in/yr |
|---|---|---|---|---|
| No heater | 2 | Jul to Aug | $0 | $0 |
| Solar cover only | 4 | Jun to Sep | $0 | $50 |
| Solar panels + cover | 5 | May to Sep | $0 | $283 |
| Heat pump + cover | 7 | Apr to Oct | $344 | $894 |
| Gas heater + cover | 7 | Apr to Oct | $670 | $1,095 |
For a 450 sq ft pool held at 80°F, at MO prices of 14.3¢/kWh electricity and $15/Mcf gas. All-in spreads the purchase over the equipment's life.
The cheapest way to the full season in Union
Heat pump + cover: 7 of 7 possible months for about $894 a year all-in, which works out near $179 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 a heat pump sized to your pool's surface area; here it beats gas all-in (heat pump or gas).
Weather station: Union, 0.6 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
Union 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 | 43° | 33° | 2.1 | 34° | 40° | – | – |
| Feb | 48° | 37° | 2.8 | 35° | 41° | – | – |
| Mar | 59° | 47° | 3.8 | 43° | 49° | – | – |
| Apr | 70° | 58° | 5.0 | 55° | 61° | $178 | $338 |
| May | 78° | 67° | 5.6 | 65° | 71° | $75 | $160 |
| Jun | 86° | 75° | 6.4 | 74° | 80° | – | – |
| Jul | 91° | 79° | 6.3 | 80° | 86° | – | – |
| Aug | 89° | 78° | 5.6 | 81° | 87° | – | – |
| Sep | 82° | 69° | 4.8 | 75° | 81° | – | – |
| Oct | 70° | 58° | 3.4 | 64° | 70° | $91 | $172 |
| Nov | 57° | 46° | 2.4 | 51° | 57° | – | – |
| Dec | 46° | 37° | 1.8 | 40° | 46° | – | – |
Heating costs most in Apr (about $178 with a heat pump, $338 with gas). Sunshine peaks in Jun at 6.4 kWh/m²/day (NASA satellite data, 43.7 km grid cell). Highlighted months are swimmable with no heater.
How Union compares with nearby cities
Union ranks 30 of 80 Missouri cities for unheated swim months, and no nearby city gets a longer unheated season.
| City | Distance | Unheated months | Heat pump months | Heat pump $/yr |
|---|---|---|---|---|
| Washington, MO | 8 mi | 2 | 5 | $104 |
| Eureka, MO | 19 mi | 2 | 5 | $84 |
| Wildwood, MO | 20 mi | 2 | 5 | $84 |
| Ellisville, MO | 24 mi | 2 | 5 | $84 |
| Dardenne Prairie, MO | 26 mi | 2 | 5 | $102 |
| Lake St. Louis, MO | 26 mi | 2 | 5 | $102 |