Pool swim season in San Marino, CA
When can you swim in an outdoor pool in San Marino, CA?
An unheated pool in San Marino reaches 78°F in Jul to Sep, about 3 months a year. The air allows up to 9 swimmable months with a heater (Mar to Nov).
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What each heater buys you in San Marino
| Option | Months | Swimmable | Energy/yr | All-in/yr |
|---|---|---|---|---|
| No heater | 3 | Jul to Sep | $0 | $0 |
| Solar cover only | 5 | Jun to Oct | $0 | $50 |
| Solar panels + cover | 8 | Apr to Nov | $0 | $283 |
| Heat pump + cover | 9 | Mar to Nov | $657 | $1,207 |
| Gas heater + cover | 9 | Mar to Nov | $859 | $1,284 |
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 San Marino
Solar panels + cover: 8 of 9 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 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: Pasadena, 2.5 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
San Marino 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 | 68° | 57° | 3.2 | 57° | 63° | – | – |
| Feb | 69° | 58° | 4.0 | 58° | 64° | – | – |
| Mar | 73° | 61° | 5.4 | 62° | 68° | $251 | $319 |
| Apr | 76° | 63° | 6.6 | 66° | 72° | $162 | $214 |
| May | 78° | 66° | 7.5 | 69° | 75° | $88 | $121 |
| Jun | 84° | 71° | 8.1 | 74° | 80° | $9 | $13 |
| Jul | 89° | 76° | 7.9 | 78° | 84° | – | – |
| Aug | 91° | 77° | 7.4 | 81° | 87° | – | – |
| Sep | 90° | 76° | 6.3 | 80° | 86° | – | – |
| Oct | 83° | 70° | 4.8 | 75° | 81° | – | – |
| Nov | 75° | 62° | 3.6 | 67° | 73° | $147 | $192 |
| Dec | 67° | 56° | 2.9 | 59° | 65° | – | – |
Heating costs most in Mar (about $251 with a heat pump, $319 with gas). Sunshine peaks in Jun at 8.1 kWh/m²/day (NASA satellite data, 55.0 km grid cell). Highlighted months are swimmable with no heater.
How San Marino compares with nearby cities
San Marino ranks 134 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 Gabriel, CA | 2 mi | 3 | 9 | $650 |
| South Pasadena, CA | 3 mi | 3 | 9 | $657 |
| Pasadena, CA | 3 mi | 3 | 9 | $657 |
| Alhambra, CA | 3 mi | 3 | 9 | $650 |
| Temple City, CA | 3 mi | 3 | 9 | $650 |
| Rosemead, CA | 4 mi | 3 | 9 | $650 |