Pool swim season in Dover, NH
Dover, NH: how long the pool season really is
An unheated pool in Dover never reaches 78°F in a normal year. It peaks around 71°F in Aug. The air allows up to 4 swimmable months with a heater (Jun to Sep).
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What each heater buys you in Dover
| Option | Months | Swimmable | Energy/yr | All-in/yr |
|---|---|---|---|---|
| No heater | 0 | no month | $0 | $0 |
| Solar cover only | 0 | no month | $0 | $50 |
| Solar panels + cover | 3 | Jul to Sep | $0 | $283 |
| Heat pump + cover | 4 | Jun to Sep | $418 | $968 |
| Gas heater + cover | 4 | Jun to Sep | $576 | $1,001 |
For a 450 sq ft pool held at 80°F, at NH prices of 26.9¢/kWh electricity and $19/Mcf gas. All-in spreads the purchase over the equipment's life.
The cheapest way to the full season in Dover
Solar panels + cover: 3 of 4 possible months for about $283 a year all-in, which works out near $94 for each month it adds.
A solar cover alone adds no swim months here, so if you want a longer season you need a heater (why); still use one at night to hold the heat you pay for. 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: Durham 2 N, 2.4 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
Dover 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 | 32° | 24° | 1.7 | 25° | 31° | – | – |
| Feb | 36° | 26° | 2.5 | 24° | 30° | – | – |
| Mar | 43° | 34° | 3.7 | 31° | 37° | – | – |
| Apr | 55° | 45° | 4.7 | 41° | 47° | – | – |
| May | 66° | 55° | 5.3 | 52° | 58° | – | – |
| Jun | 75° | 64° | 5.6 | 62° | 68° | $186 | $255 |
| Jul | 81° | 70° | 5.9 | 70° | 76° | $61 | $91 |
| Aug | 80° | 69° | 5.3 | 71° | 77° | $38 | $56 |
| Sep | 72° | 61° | 4.3 | 66° | 72° | $133 | $174 |
| Oct | 60° | 50° | 2.8 | 55° | 61° | – | – |
| Nov | 48° | 39° | 1.8 | 43° | 49° | – | – |
| Dec | 38° | 30° | 1.4 | 33° | 39° | – | – |
Heating costs most in Jun (about $186 with a heat pump, $255 with gas). Sunshine peaks in Jul at 5.9 kWh/m²/day (NASA satellite data, 46.7 km grid cell). Highlighted months are swimmable with no heater.
How Dover compares with nearby cities
Dover ranks 9 of 11 New Hampshire cities for unheated swim months, and no nearby city gets a longer unheated season.
| City | Distance | Unheated months | Heat pump months | Heat pump $/yr |
|---|---|---|---|---|
| Somersworth, NH | 5 mi | 0 | 4 | $347 |
| Rochester, NH | 9 mi | 0 | 4 | $347 |
| Portsmouth, NH | 10 mi | 0 | 4 | $381 |
| Sanford, ME | 18 mi | 0 | 4 | $541 |
| Amesbury, MA | 23 mi | 0 | 4 | $350 |
| Newburyport, MA | 26 mi | 0 | 4 | $292 |