Pool swim season in Cambridge, MA
When can you swim in an outdoor pool in Cambridge, MA?
An unheated pool in Cambridge 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).
- J
- F
- M
- A
- M
- J
- J
- A
- S
- O
- N
- D
Heater options for a Cambridge pool, side by side
| 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 | $193 | $743 |
| Gas heater + cover | 4 | Jun to Sep | $331 | $756 |
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 Cambridge
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: Jamaica Plain, 5 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
Cambridge 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° | 28° | 1.8 | 30° | 36° | – | – |
| Feb | 40° | 30° | 2.7 | 29° | 35° | – | – |
| Mar | 47° | 38° | 3.7 | 35° | 41° | – | – |
| Apr | 59° | 49° | 4.7 | 45° | 51° | – | – |
| May | 69° | 59° | 5.3 | 56° | 62° | – | – |
| Jun | 79° | 68° | 5.7 | 66° | 72° | $128 | $223 |
| Jul | 85° | 74° | 6.0 | 74° | 80° | – | – |
| Aug | 83° | 73° | 5.3 | 76° | 82° | – | – |
| Sep | 76° | 65° | 4.3 | 70° | 76° | $65 | $108 |
| Oct | 64° | 53° | 2.8 | 59° | 65° | – | – |
| Nov | 53° | 43° | 2.0 | 47° | 53° | – | – |
| Dec | 42° | 34° | 1.5 | 37° | 43° | – | – |
Heating costs most in Jun (about $128 with a heat pump, $223 with gas). Sunshine peaks in Jul at 6.0 kWh/m²/day (NASA satellite data, 34.2 km grid cell). Highlighted months are swimmable with no heater.
How Cambridge compares with nearby cities
Cambridge ranks 1 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 |
|---|---|---|---|---|
| Somerville, MA | 1 mi | 0 | 4 | $197 |
| Watertown, MA | 3 mi | 0 | 4 | $193 |
| Medford, MA | 3 mi | 0 | 4 | $197 |
| Everett, MA | 4 mi | 0 | 4 | $197 |
| Chelsea, MA | 5 mi | 0 | 4 | $197 |
| Malden, MA | 5 mi | 0 | 4 | $197 |