Pool swim season in Marlborough, MA
Marlborough, MA: how long the pool season really is
An unheated pool in Marlborough never reaches 78°F in a normal year. It peaks around 75°F in Aug. The air allows up to 5 swimmable months with a heater (May to Sep).
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Heater options for a Marlborough 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 | 5 | May to Sep | $573 | $1,123 |
| Gas heater + cover | 5 | May to Sep | $916 | $1,341 |
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 Marlborough
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: Maynard 2, 7.7 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
Marlborough 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° | 26° | 1.8 | 28° | 34° | – | – |
| Feb | 41° | 28° | 2.7 | 27° | 33° | – | – |
| Mar | 49° | 36° | 3.7 | 33° | 39° | – | – |
| Apr | 62° | 48° | 4.7 | 44° | 50° | – | – |
| May | 73° | 59° | 5.3 | 56° | 62° | $345 | $530 |
| Jun | 81° | 68° | 5.7 | 66° | 72° | $130 | $224 |
| Jul | 87° | 74° | 6.0 | 74° | 80° | $5 | $10 |
| Aug | 85° | 72° | 5.3 | 75° | 81° | – | – |
| Sep | 78° | 64° | 4.3 | 69° | 75° | $93 | $152 |
| Oct | 66° | 52° | 2.8 | 57° | 63° | – | – |
| Nov | 54° | 41° | 2.0 | 45° | 51° | – | – |
| Dec | 43° | 32° | 1.5 | 35° | 41° | – | – |
Heating costs most in May (about $345 with a heat pump, $530 with gas). Sunshine peaks in Jul at 6.0 kWh/m²/day (NASA satellite data, 17.2 km grid cell). Highlighted months are swimmable with no heater.
How Marlborough compares with nearby cities
Marlborough ranks 22 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 |
|---|---|---|---|---|
| Framingham, MA | 6 mi | 0 | 4 | $335 |
| Worcester, MA | 14 mi | 0 | 4 | $386 |
| Waltham, MA | 16 mi | 0 | 5 | $575 |
| Leominster, MA | 16 mi | 0 | 4 | $282 |
| Newton, MA | 17 mi | 0 | 4 | $193 |
| Watertown, MA | 19 mi | 0 | 4 | $193 |