Pool swim season in St. Louis, MO
Swim season in St. Louis without a heater, and with one
An unheated pool in St. Louis 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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What each heater buys you in St. Louis
| 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 | 5 | May to Sep | $68 | $618 |
| Gas heater + cover | 5 | May to Sep | $147 | $572 |
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 St. Louis
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: St Louis Sci Center, 1.5 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
St. Louis 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 | 41° | 33° | 2.1 | 34° | 40° | – | – |
| Feb | 46° | 37° | 2.8 | 35° | 41° | – | – |
| Mar | 56° | 47° | 3.8 | 43° | 49° | – | – |
| Apr | 68° | 58° | 5.0 | 54° | 60° | – | – |
| May | 77° | 68° | 5.6 | 66° | 72° | $68 | $147 |
| Jun | 86° | 77° | 6.4 | 76° | 82° | – | – |
| Jul | 90° | 81° | 6.3 | 82° | 88° | – | – |
| Aug | 89° | 79° | 5.6 | 83° | 89° | – | – |
| Sep | 82° | 72° | 4.8 | 77° | 83° | – | – |
| Oct | 70° | 60° | 3.4 | 66° | 72° | – | – |
| Nov | 56° | 48° | 2.4 | 53° | 59° | – | – |
| Dec | 45° | 37° | 1.8 | 41° | 47° | – | – |
Heating costs most in May (about $68 with a heat pump, $147 with gas). Sunshine peaks in Jun at 6.4 kWh/m²/day (NASA satellite data, 26.8 km grid cell). Highlighted months are swimmable with no heater.
How St. Louis compares with nearby cities
St. Louis ranks 5 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 |
|---|---|---|---|---|
| Clayton, MO | 5 mi | 2 | 5 | $68 |
| University City, MO | 5 mi | 2 | 5 | $68 |
| Jennings, MO | 6 mi | 2 | 5 | $71 |
| East St. Louis, IL | 6 mi | 2 | 5 | $107 |
| Cahokia Heights, IL | 7 mi | 2 | 5 | $107 |
| Webster Groves, MO | 7 mi | 2 | 5 | $68 |