Pool swim season in St. Marys, PA
Swim season in St. Marys without a heater, and with one
An unheated pool in St. Marys never reaches 78°F in a normal year. It peaks around 68°F in Aug. The air allows up to 4 swimmable months with a heater (Jun to Sep).
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What each heater buys you in St. Marys
| Option | Months | Swimmable | Energy/yr | All-in/yr |
|---|---|---|---|---|
| No heater | 0 | no month | $0 | $0 |
| Solar cover only | 0 | no month | $0 | $50 |
| Solar panels + cover | 2 | Jul to Aug | $0 | $283 |
| Heat pump + cover | 4 | Jun to Sep | $441 | $991 |
| Gas heater + cover | 4 | Jun to Sep | $612 | $1,037 |
For a 450 sq ft pool held at 80°F, at PA prices of 21.1¢/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. Marys
Heat pump + cover: 4 of 4 possible months for about $991 a year all-in, which works out near $248 for each month it adds.
A solar cover alone adds no swim months here, so if you want a longer season you need a heater (why); still use one at night to hold the heat you pay for. 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: Glen Hazel 2 NE Dam, 8.4 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
St. Marys 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 | 31° | 22° | 1.5 | 23° | 29° | – | – |
| Feb | 33° | 23° | 2.3 | 22° | 28° | – | – |
| Mar | 43° | 32° | 3.3 | 28° | 34° | – | – |
| Apr | 56° | 44° | 4.5 | 39° | 45° | – | – |
| May | 67° | 55° | 5.2 | 51° | 57° | – | – |
| Jun | 75° | 63° | 5.8 | 62° | 68° | $157 | $218 |
| Jul | 79° | 67° | 5.8 | 68° | 74° | $76 | $112 |
| Aug | 77° | 66° | 5.1 | 68° | 74° | $69 | $99 |
| Sep | 71° | 59° | 4.1 | 64° | 70° | $139 | $183 |
| Oct | 59° | 48° | 2.7 | 53° | 59° | – | – |
| Nov | 46° | 37° | 1.8 | 41° | 47° | – | – |
| Dec | 35° | 27° | 1.2 | 30° | 36° | – | – |
Heating costs most in Jun (about $157 with a heat pump, $218 with gas). Sunshine peaks in Jul at 5.8 kWh/m²/day (NASA satellite data, 5.3 km grid cell). Highlighted months are swimmable with no heater.
How St. Marys compares with nearby cities
St. Marys ranks 68 of 68 Pennsylvania cities for unheated swim months, and no nearby city gets a longer unheated season.
| City | Distance | Unheated months | Heat pump months | Heat pump $/yr |
|---|---|---|---|---|
| Olean, NY | 44 mi | 0 | 4 | $490 |
| State College, PA | 57 mi | 0 | 4 | $174 |
| Jamestown, NY | 58 mi | 0 | 4 | $437 |
| Altoona, PA | 66 mi | 0 | 4 | $212 |
| Indiana, PA | 66 mi | 0 | 5 | $475 |
| Williamsport, PA | 78 mi | 0 | 5 | $304 |