Pool swim season in Danville, CA
When can you swim in an outdoor pool in Danville, CA?
An unheated pool in Danville never reaches 78°F in a normal year. It peaks around 76°F in Aug. The air allows up to 5 swimmable months with a heater (Jun to Oct).
- J
- F
- M
- A
- M
- J
- J
- A
- S
- O
- N
- D
Heater options for a Danville pool, side by side
| 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 | 5 | Jun to Oct | $0 | $283 |
| Heat pump + cover | 5 | Jun to Oct | $245 | $795 |
| Gas heater + cover | 5 | Jun to Oct | $328 | $753 |
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 Danville
Solar panels + cover: 5 of 5 possible months for about $283 a year all-in, which works out near $57 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 gas as well as a heat pump: once the purchase price is counted, gas comes out cheaper all-in here (heat pump or gas).
Weather station: Mt Diablo Junction, 5.1 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
Danville 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 | 54° | 48° | 2.4 | 47° | 53° | – | – |
| Feb | 55° | 48° | 3.5 | 48° | 54° | – | – |
| Mar | 58° | 50° | 4.8 | 51° | 57° | – | – |
| Apr | 62° | 53° | 6.2 | 55° | 61° | – | – |
| May | 68° | 59° | 7.5 | 60° | 66° | – | – |
| Jun | 76° | 66° | 8.3 | 67° | 73° | $123 | $168 |
| Jul | 83° | 72° | 8.2 | 74° | 80° | – | – |
| Aug | 83° | 72° | 7.4 | 76° | 82° | – | – |
| Sep | 80° | 70° | 6.0 | 74° | 80° | $2 | $2 |
| Oct | 72° | 63° | 4.4 | 68° | 74° | $120 | $158 |
| Nov | 60° | 53° | 2.9 | 58° | 64° | – | – |
| Dec | 53° | 47° | 2.2 | 50° | 56° | – | – |
Heating costs most in Jun (about $123 with a heat pump, $168 with gas). Sunshine peaks in Jun at 8.3 kWh/m²/day (NASA satellite data, 54.0 km grid cell). Highlighted months are swimmable with no heater.
How Danville compares with nearby cities
Danville ranks 230 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 |
|---|---|---|---|---|
| San Ramon, CA | 4 mi | 0 | 5 | $245 |
| Walnut Creek, CA | 7 mi | 0 | 7 | $483 |
| Dublin, CA | 8 mi | 0 | 6 | $366 |
| Moraga, CA | 9 mi | 0 | 6 | $995 |
| Clayton, CA | 9 mi | 0 | 5 | $245 |
| Lafayette, CA | 10 mi | 0 | 7 | $483 |