Pool swim season in Troy, MO
When can you swim in an outdoor pool in Troy, MO?
An unheated pool in Troy 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 Troy
| 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 | 4 | Jun to Sep | $0 | $283 |
| Heat pump + cover | 5 | May to Sep | $118 | $668 |
| Gas heater + cover | 5 | May to Sep | $248 | $673 |
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 Troy
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 a heat pump sized to your pool's surface area; here it beats gas all-in (heat pump or gas).
Weather station: Warrenton 1 N, 13.1 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
Troy 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 | 39° | 29° | 2.1 | 31° | 37° | – | – |
| Feb | 44° | 34° | 2.8 | 31° | 37° | – | – |
| Mar | 55° | 44° | 3.8 | 40° | 46° | – | – |
| Apr | 66° | 55° | 5.0 | 51° | 57° | – | – |
| May | 75° | 64° | 5.6 | 62° | 68° | $100 | $206 |
| Jun | 84° | 73° | 6.4 | 72° | 78° | $14 | $33 |
| Jul | 88° | 77° | 6.3 | 79° | 85° | – | – |
| Aug | 87° | 76° | 5.6 | 79° | 85° | – | – |
| Sep | 80° | 68° | 4.8 | 74° | 80° | $4 | $9 |
| Oct | 68° | 56° | 3.4 | 63° | 69° | – | – |
| Nov | 55° | 44° | 2.4 | 50° | 56° | – | – |
| Dec | 43° | 34° | 1.8 | 38° | 44° | – | – |
Heating costs most in May (about $100 with a heat pump, $206 with gas). Sunshine peaks in Jun at 6.4 kWh/m²/day (NASA satellite data, 66.1 km grid cell). Highlighted months are swimmable with no heater.
How Troy compares with nearby cities
Troy ranks 73 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 |
|---|---|---|---|---|
| Wentzville, MO | 12 mi | 2 | 5 | $102 |
| Lake St. Louis, MO | 16 mi | 2 | 5 | $102 |
| O'Fallon, MO | 19 mi | 2 | 5 | $102 |
| Dardenne Prairie, MO | 21 mi | 2 | 5 | $102 |
| St. Peters, MO | 23 mi | 2 | 5 | $102 |
| St. Charles, MO | 27 mi | 2 | 5 | $94 |