Pool swim season in Fairfax, VA
Fairfax, VA: how long the pool season really is
An unheated pool in Fairfax never reaches 78°F in a normal year. It peaks around 77°F in Aug. The air allows up to 5 swimmable months with a heater (May to Sep).
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Heater options for a Fairfax 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 | $211 | $761 |
| Gas heater + cover | 5 | May to Sep | $414 | $839 |
For a 450 sq ft pool held at 80°F, at VA prices of 16.9¢/kWh electricity and $17/Mcf gas. All-in spreads the purchase over the equipment's life.
The cheapest way to the full season in Fairfax
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 a heat pump sized to your pool's surface area; here it beats gas all-in (heat pump or gas).
Weather station: Vienna, 2.7 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
Fairfax 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 | 42° | 33° | 2.2 | 34° | 40° | – | – |
| Feb | 45° | 35° | 3.0 | 34° | 40° | – | – |
| Mar | 53° | 42° | 4.0 | 40° | 46° | – | – |
| Apr | 65° | 53° | 5.0 | 50° | 56° | – | – |
| May | 72° | 62° | 5.6 | 60° | 66° | $143 | $272 |
| Jun | 80° | 70° | 6.2 | 69° | 75° | $43 | $92 |
| Jul | 84° | 75° | 6.0 | 76° | 82° | – | – |
| Aug | 82° | 74° | 5.4 | 77° | 83° | – | – |
| Sep | 76° | 67° | 4.4 | 71° | 77° | $25 | $50 |
| Oct | 65° | 55° | 3.3 | 61° | 67° | – | – |
| Nov | 56° | 45° | 2.5 | 50° | 56° | – | – |
| Dec | 46° | 37° | 1.9 | 40° | 46° | – | – |
Heating costs most in May (about $143 with a heat pump, $272 with gas). Sunshine peaks in Jun at 6.2 kWh/m²/day (NASA satellite data, 43.0 km grid cell). Highlighted months are swimmable with no heater.
How Fairfax compares with nearby cities
Fairfax ranks 28 of 39 Virginia cities for unheated swim months; Falls Church, Herndon, Manassas Park nearby get a longer season without a heater.
| City | Distance | Unheated months | Heat pump months | Heat pump $/yr |
|---|---|---|---|---|
| Vienna, VA | 4 mi | 0 | 5 | $211 |
| Falls Church, VA | 7 mi | 2 | 5 | $126 |
| Herndon, VA | 9 mi | 1 | 5 | $145 |
| Manassas Park, VA | 10 mi | 2 | 5 | $144 |
| Alexandria, VA | 12 mi | 2 | 5 | $83 |
| Manassas, VA | 12 mi | 2 | 5 | $144 |