Pool swim season in Napa, CA
Swim season in Napa without a heater, and with one
An unheated pool in Napa never reaches 78°F in a normal year. It peaks around 74°F in Jul. The air allows up to 7 swimmable months with a heater (Apr to Oct).
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What each heater buys you in Napa
| Option | Months | Swimmable | Energy/yr | All-in/yr |
|---|---|---|---|---|
| No heater | 0 | no month | $0 | $0 |
| Solar cover only | 3 | Jul to Sep | $0 | $50 |
| Solar panels + cover | 6 | May to Oct | $0 | $283 |
| Heat pump + cover | 7 | Apr to Oct | $680 | $1,230 |
| Gas heater + cover | 7 | Apr to Oct | $889 | $1,314 |
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 Napa
Solar panels + cover: 6 of 7 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 3 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: Napa State Hospital, 2.4 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
Napa 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 | 59° | 49° | 2.3 | 49° | 55° | – | – |
| Feb | 63° | 53° | 3.3 | 51° | 57° | – | – |
| Mar | 68° | 56° | 4.6 | 56° | 62° | – | – |
| Apr | 72° | 59° | 6.1 | 60° | 66° | $282 | $351 |
| May | 77° | 63° | 7.3 | 65° | 71° | $168 | $222 |
| Jun | 82° | 68° | 8.1 | 71° | 77° | $59 | $83 |
| Jul | 83° | 69° | 8.0 | 74° | 80° | $5 | $7 |
| Aug | 84° | 70° | 7.1 | 74° | 80° | $7 | $11 |
| Sep | 84° | 69° | 5.8 | 72° | 78° | $34 | $49 |
| Oct | 78° | 64° | 4.2 | 68° | 74° | $125 | $166 |
| Nov | 66° | 55° | 2.8 | 59° | 65° | – | – |
| Dec | 59° | 49° | 2.0 | 51° | 57° | – | – |
Heating costs most in Apr (about $282 with a heat pump, $351 with gas). Sunshine peaks in Jun at 8.1 kWh/m²/day (NASA satellite data, 28.4 km grid cell). Highlighted months are swimmable with no heater.
How Napa compares with nearby cities
Napa ranks 279 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 |
|---|---|---|---|---|
| American Canyon, CA | 9 mi | 0 | 6 | $738 |
| Sonoma, CA | 9 mi | 0 | 6 | $496 |
| Vallejo, CA | 13 mi | 0 | 7 | $501 |
| Fairfield, CA | 15 mi | 0 | 7 | $506 |
| Suisun City, CA | 16 mi | 0 | 7 | $506 |
| Benicia, CA | 17 mi | 0 | 7 | $501 |