Pool swim season in Boston, MA
Boston, MA: how long the pool season really is
An unheated pool in Boston never reaches 78°F in a normal year. It peaks around 76°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 Boston
| 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 | 4 | Jun to Sep | $197 | $747 |
| Gas heater + cover | 4 | Jun to Sep | $339 | $764 |
For a 450 sq ft pool held at 80°F, at MA prices of 30.2¢/kWh electricity and $25/Mcf gas. All-in spreads the purchase over the equipment's life.
The cheapest way to the full season in Boston
Solar panels + cover: 4 of 4 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: Boston, 1.6 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
Boston 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 | 37° | 30° | 1.8 | 32° | 38° | – | – |
| Feb | 39° | 32° | 2.7 | 31° | 37° | – | – |
| Mar | 46° | 38° | 3.7 | 36° | 42° | – | – |
| Apr | 56° | 49° | 4.7 | 45° | 51° | – | – |
| May | 67° | 58° | 5.3 | 56° | 62° | – | – |
| Jun | 76° | 68° | 5.7 | 66° | 72° | $135 | $235 |
| Jul | 82° | 74° | 6.0 | 74° | 80° | – | – |
| Aug | 80° | 73° | 5.3 | 76° | 82° | – | – |
| Sep | 73° | 66° | 4.3 | 70° | 76° | $62 | $104 |
| Oct | 62° | 55° | 2.8 | 60° | 66° | – | – |
| Nov | 52° | 45° | 2.0 | 49° | 55° | – | – |
| Dec | 42° | 36° | 1.5 | 39° | 45° | – | – |
Heating costs most in Jun (about $135 with a heat pump, $235 with gas). Sunshine peaks in Jul at 6.0 kWh/m²/day (NASA satellite data, 43.4 km grid cell). Highlighted months are swimmable with no heater.
How Boston compares with nearby cities
Boston ranks 6 of 58 Massachusetts cities for unheated swim months, and no nearby city gets a longer unheated season.
| City | Distance | Unheated months | Heat pump months | Heat pump $/yr |
|---|---|---|---|---|
| Winthrop Town, MA | 4 mi | 0 | 4 | $195 |
| Chelsea, MA | 4 mi | 0 | 4 | $197 |
| Everett, MA | 5 mi | 0 | 4 | $197 |
| Quincy, MA | 5 mi | 0 | 4 | $236 |
| Somerville, MA | 6 mi | 0 | 4 | $197 |
| Cambridge, MA | 6 mi | 0 | 4 | $193 |