Pool swim season in Wilmington, DE
Wilmington, DE: how long the pool season really is
An unheated pool in Wilmington 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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What each heater buys you in Wilmington
| 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 | $230 | $780 |
| Gas heater + cover | 5 | May to Sep | $404 | $829 |
For a 450 sq ft pool held at 80°F, at DE prices of 18.0¢/kWh electricity and $16/Mcf gas. All-in spreads the purchase over the equipment's life.
The cheapest way to the full season in Wilmington
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: Wilmington Porter Research, 2.7 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
Wilmington 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 | 38° | 31° | 2.0 | 32° | 38° | – | – |
| Feb | 41° | 33° | 2.9 | 32° | 38° | – | – |
| Mar | 49° | 41° | 3.8 | 38° | 44° | – | – |
| Apr | 61° | 52° | 5.0 | 48° | 54° | – | – |
| May | 71° | 62° | 5.6 | 59° | 65° | $161 | $274 |
| Jun | 79° | 71° | 6.2 | 69° | 75° | $46 | $88 |
| Jul | 84° | 76° | 6.2 | 76° | 82° | – | – |
| Aug | 82° | 74° | 5.4 | 77° | 83° | – | – |
| Sep | 75° | 67° | 4.4 | 72° | 78° | $23 | $42 |
| Oct | 63° | 55° | 3.2 | 61° | 67° | – | – |
| Nov | 53° | 45° | 2.3 | 49° | 55° | – | – |
| Dec | 43° | 36° | 1.8 | 39° | 45° | – | – |
Heating costs most in May (about $161 with a heat pump, $274 with gas). Sunshine peaks in Jun at 6.2 kWh/m²/day (NASA satellite data, 26.4 km grid cell). Highlighted months are swimmable with no heater.
How Wilmington compares with nearby cities
Wilmington ranks 6 of 6 Delaware cities for unheated swim months; Chester, Newark, Elkton nearby get a longer season without a heater.
| City | Distance | Unheated months | Heat pump months | Heat pump $/yr |
|---|---|---|---|---|
| Chester, PA | 11 mi | 2 | 5 | $151 |
| Newark, DE | 13 mi | 2 | 5 | $158 |
| West Chester, PA | 16 mi | 0 | 5 | $301 |
| Elkton, MD | 18 mi | 2 | 5 | $186 |
| Darby, PA | 19 mi | 2 | 5 | $169 |
| Lansdowne, PA | 20 mi | 2 | 5 | $169 |