Pool swim season in Annapolis, MD
When can you swim in an outdoor pool in Annapolis, MD?
An unheated pool in Annapolis 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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Heater options for a Annapolis pool, side by side
| 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 | $105 | $655 |
| Gas heater + cover | 5 | May to Sep | $164 | $589 |
For a 450 sq ft pool held at 80°F, at MD prices of 21.3¢/kWh electricity and $16/Mcf gas. All-in spreads the purchase over the equipment's life.
The cheapest way to the full season in Annapolis
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: Annapolis Police Brks, 1.5 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
Annapolis 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 | 44° | 37° | 2.2 | 38° | 44° | – | – |
| Feb | 48° | 39° | 3.0 | 38° | 44° | – | – |
| Mar | 55° | 47° | 4.0 | 44° | 50° | – | – |
| Apr | 68° | 58° | 5.1 | 55° | 61° | – | – |
| May | 77° | 67° | 5.8 | 65° | 71° | $105 | $164 |
| Jun | 85° | 76° | 6.4 | 75° | 81° | – | – |
| Jul | 89° | 80° | 6.3 | 81° | 87° | – | – |
| Aug | 86° | 78° | 5.6 | 82° | 88° | – | – |
| Sep | 80° | 72° | 4.5 | 77° | 83° | – | – |
| Oct | 69° | 60° | 3.4 | 67° | 73° | – | – |
| Nov | 58° | 49° | 2.5 | 54° | 60° | – | – |
| Dec | 48° | 41° | 1.9 | 44° | 50° | – | – |
Heating costs most in May (about $105 with a heat pump, $164 with gas). Sunshine peaks in Jun at 6.4 kWh/m²/day (NASA satellite data, 52.5 km grid cell). Highlighted months are swimmable with no heater.
How Annapolis compares with nearby cities
Annapolis ranks 3 of 23 Maryland cities for unheated swim months, and no nearby city gets a longer unheated season.
| City | Distance | Unheated months | Heat pump months | Heat pump $/yr |
|---|---|---|---|---|
| Bowie, MD | 13 mi | 1 | 5 | $204 |
| New Carrollton, MD | 20 mi | 1 | 5 | $204 |
| Greenbelt, MD | 20 mi | 2 | 5 | $173 |
| Laurel, MD | 21 mi | 2 | 5 | $143 |
| College Park, MD | 23 mi | 2 | 5 | $173 |
| Baltimore, MD | 23 mi | 2 | 5 | $111 |