Pool swim season in Washington, DC
When can you swim in an outdoor pool in Washington, DC?
An unheated pool in Washington 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 Washington
| 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 | $134 | $684 |
| Gas heater + cover | 5 | May to Sep | $185 | $610 |
For a 450 sq ft pool held at 80°F, at DC prices of 24.9¢/kWh electricity and $17/Mcf gas. All-in spreads the purchase over the equipment's life.
The cheapest way to the full season in Washington
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: Natl Arboretum Dc, 2.6 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
Washington 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 | 45° | 36° | 2.2 | 38° | 44° | – | – |
| Feb | 48° | 39° | 3.0 | 37° | 43° | – | – |
| Mar | 56° | 46° | 4.0 | 43° | 49° | – | – |
| Apr | 68° | 57° | 5.0 | 54° | 60° | – | – |
| May | 77° | 67° | 5.6 | 64° | 70° | $134 | $185 |
| Jun | 85° | 76° | 6.2 | 74° | 80° | – | – |
| Jul | 90° | 80° | 6.0 | 81° | 87° | – | – |
| Aug | 88° | 79° | 5.4 | 82° | 88° | – | – |
| Sep | 82° | 72° | 4.4 | 77° | 83° | – | – |
| Oct | 70° | 59° | 3.3 | 66° | 72° | – | – |
| Nov | 58° | 49° | 2.5 | 54° | 60° | – | – |
| Dec | 49° | 41° | 1.9 | 44° | 50° | – | – |
Heating costs most in May (about $134 with a heat pump, $185 with gas). Sunshine peaks in Jun at 6.2 kWh/m²/day (NASA satellite data, 61.5 km grid cell). Highlighted months are swimmable with no heater.
How Washington compares with nearby cities
Washington ranks 1 of 1 District of Columbia cities for unheated swim months, and no nearby city gets a longer unheated season.
| City | Distance | Unheated months | Heat pump months | Heat pump $/yr |
|---|---|---|---|---|
| Hyattsville, MD | 5 mi | 2 | 5 | $113 |
| Takoma Park, MD | 5 mi | 2 | 5 | $115 |
| Alexandria, VA | 7 mi | 2 | 5 | $83 |
| College Park, MD | 8 mi | 2 | 5 | $173 |
| New Carrollton, MD | 9 mi | 1 | 5 | $204 |
| Falls Church, VA | 9 mi | 2 | 5 | $126 |