Pool swim season in Sonoma, CA
Sonoma, CA: how long the pool season really is
An unheated pool in Sonoma never reaches 78°F in a normal year. It peaks around 74°F in Aug. The air allows up to 6 swimmable months with a heater (May to Oct).
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Heater options for a Sonoma 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 | 6 | May to Oct | $0 | $283 |
| Heat pump + cover | 6 | May to Oct | $496 | $1,046 |
| Gas heater + cover | 6 | May to Oct | $660 | $1,085 |
For a 450 sq ft pool held at 80°F, at CA prices of 32.6¢/kWh electricity and $22/Mcf gas. All-in spreads the purchase over the equipment's life.
The cheapest way to the full season in Sonoma
Solar panels + cover: 6 of 6 possible months for about $283 a year all-in, which works out near $47 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: Sonoma, 0.6 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
Sonoma 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 | 57° | 48° | 2.3 | 47° | 53° | – | – |
| Feb | 62° | 51° | 3.3 | 50° | 56° | – | – |
| Mar | 65° | 54° | 4.6 | 54° | 60° | – | – |
| Apr | 69° | 57° | 6.1 | 58° | 64° | – | – |
| May | 75° | 62° | 7.3 | 63° | 69° | $208 | $270 |
| Jun | 83° | 67° | 8.1 | 70° | 76° | $83 | $115 |
| Jul | 86° | 70° | 8.0 | 73° | 79° | $10 | $15 |
| Aug | 86° | 70° | 7.1 | 74° | 80° | $5 | $7 |
| Sep | 85° | 68° | 5.8 | 72° | 78° | $43 | $60 |
| Oct | 78° | 63° | 4.2 | 66° | 72° | $147 | $193 |
| Nov | 65° | 54° | 2.8 | 58° | 64° | – | – |
| Dec | 57° | 47° | 2.0 | 50° | 56° | – | – |
Heating costs most in May (about $208 with a heat pump, $270 with gas). Sunshine peaks in Jun at 8.1 kWh/m²/day (NASA satellite data, 23.6 km grid cell). Highlighted months are swimmable with no heater.
How Sonoma compares with nearby cities
Sonoma ranks 281 of 376 California cities for unheated swim months, and no nearby city gets a longer unheated season.
| City | Distance | Unheated months | Heat pump months | Heat pump $/yr |
|---|---|---|---|---|
| Napa, CA | 9 mi | 0 | 7 | $680 |
| Petaluma, CA | 10 mi | 0 | 6 | $746 |
| American Canyon, CA | 13 mi | 0 | 6 | $738 |
| Rohnert Park, CA | 14 mi | 0 | 7 | $934 |
| Novato, CA | 15 mi | 0 | 6 | $575 |
| Vallejo, CA | 17 mi | 0 | 7 | $501 |