Pool swim season in San Mateo, CA
When can you swim in an outdoor pool in San Mateo, CA?
An unheated pool in San Mateo never reaches 78°F in a normal year. It peaks around 67°F in Aug. The air allows up to 5 swimmable months with a heater (Jun to Oct).
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What each heater buys you in San Mateo
| Option | Months | Swimmable | Energy/yr | All-in/yr |
|---|---|---|---|---|
| No heater | 0 | no month | $0 | $0 |
| Solar cover only | 0 | no month | $0 | $50 |
| Solar panels + cover | 4 | Jun to Sep | $0 | $283 |
| Heat pump + cover | 5 | Jun to Oct | $731 | $1,281 |
| Gas heater + cover | 5 | Jun to Oct | $974 | $1,399 |
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 Mateo
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.
A solar cover alone adds no swim months here, so if you want a longer season you need a heater (why); still use one at night to hold the heat you pay for. 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: San Francisco International Airport, 5.1 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
San Mateo 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 | 58° | 51° | 2.5 | 51° | 57° | – | – |
| Feb | 61° | 54° | 3.4 | 53° | 59° | – | – |
| Mar | 63° | 56° | 4.6 | 56° | 62° | – | – |
| Apr | 66° | 57° | 6.0 | 59° | 65° | – | – |
| May | 68° | 60° | 6.7 | 62° | 68° | – | – |
| Jun | 72° | 63° | 7.3 | 66° | 72° | $166 | $217 |
| Jul | 73° | 64° | 6.5 | 67° | 73° | $138 | $184 |
| Aug | 73° | 65° | 5.8 | 67° | 73° | $127 | $172 |
| Sep | 75° | 65° | 5.1 | 67° | 73° | $127 | $173 |
| Oct | 72° | 63° | 4.0 | 65° | 71° | $173 | $228 |
| Nov | 64° | 56° | 2.8 | 60° | 66° | – | – |
| Dec | 58° | 51° | 2.1 | 53° | 59° | – | – |
Heating costs most in Oct (about $173 with a heat pump, $228 with gas). Sunshine peaks in Jun at 7.3 kWh/m²/day (NASA satellite data, 18.0 km grid cell). Highlighted months are swimmable with no heater.
How San Mateo compares with nearby cities
San Mateo ranks 344 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 |
|---|---|---|---|---|
| Hillsborough, CA | 3 mi | 0 | 5 | $731 |
| Foster City, CA | 3 mi | 0 | 6 | $660 |
| Belmont, CA | 3 mi | 0 | 6 | $660 |
| Burlingame, CA | 4 mi | 0 | 5 | $731 |
| San Carlos, CA | 5 mi | 0 | 6 | $660 |
| Millbrae, CA | 6 mi | 0 | 5 | $731 |