Pool swim season in Frederick, MD
Swim season in Frederick without a heater, and with one
An unheated pool in Frederick 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 Frederick
| 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 | $131 | $681 |
| Gas heater + cover | 5 | May to Sep | $203 | $628 |
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 Frederick
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: Frederick Police Brks, 2 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
Frederick 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 | 43° | 35° | 2.0 | 36° | 42° | – | – |
| Feb | 48° | 38° | 2.8 | 36° | 42° | – | – |
| Mar | 55° | 46° | 3.8 | 43° | 49° | – | – |
| Apr | 69° | 57° | 4.9 | 53° | 59° | – | – |
| May | 77° | 66° | 5.4 | 64° | 70° | $123 | $189 |
| Jun | 85° | 74° | 6.1 | 73° | 79° | $8 | $14 |
| Jul | 89° | 79° | 6.0 | 79° | 85° | – | – |
| Aug | 87° | 77° | 5.3 | 80° | 86° | – | – |
| Sep | 80° | 70° | 4.3 | 74° | 80° | – | – |
| Oct | 69° | 58° | 3.1 | 64° | 70° | – | – |
| Nov | 56° | 47° | 2.3 | 52° | 58° | – | – |
| Dec | 47° | 39° | 1.7 | 42° | 48° | – | – |
Heating costs most in May (about $123 with a heat pump, $189 with gas). Sunshine peaks in Jun at 6.1 kWh/m²/day (NASA satellite data, 10.3 km grid cell). Highlighted months are swimmable with no heater.
How Frederick compares with nearby cities
Frederick ranks 9 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 |
|---|---|---|---|---|
| Hagerstown, MD | 22 mi | 0 | 5 | $221 |
| Gaithersburg, MD | 23 mi | 2 | 5 | $170 |
| Waynesboro, PA | 24 mi | 0 | 5 | $313 |
| Westminster, MD | 24 mi | 0 | 5 | $302 |
| Leesburg, VA | 24 mi | 0 | 5 | $198 |
| Rockville, MD | 28 mi | 2 | 5 | $170 |