Pool swim season in Gilroy, CA
When can you swim in an outdoor pool in Gilroy, CA?
An unheated pool in Gilroy never reaches 78°F in a normal year. It peaks around 75°F in Aug. The air allows up to 7 swimmable months with a heater (Apr to Oct).
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What each heater buys you in Gilroy
| 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 | $673 | $1,223 |
| Gas heater + cover | 7 | Apr to Oct | $873 | $1,298 |
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 Gilroy
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: Gilroy, 1.4 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
Gilroy 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 | 61° | 49° | 2.4 | 49° | 55° | – | – |
| Feb | 64° | 52° | 3.5 | 51° | 57° | – | – |
| Mar | 68° | 55° | 4.8 | 56° | 62° | – | – |
| Apr | 72° | 58° | 6.2 | 60° | 66° | $290 | $358 |
| May | 77° | 63° | 7.5 | 65° | 71° | $171 | $226 |
| Jun | 83° | 67° | 8.3 | 71° | 77° | $64 | $90 |
| Jul | 87° | 71° | 8.2 | 74° | 80° | – | – |
| Aug | 87° | 71° | 7.4 | 75° | 81° | – | – |
| Sep | 85° | 69° | 6.0 | 73° | 79° | $22 | $32 |
| Oct | 79° | 63° | 4.4 | 68° | 74° | $126 | $167 |
| Nov | 68° | 55° | 2.9 | 59° | 65° | – | – |
| Dec | 60° | 49° | 2.2 | 51° | 57° | – | – |
Heating costs most in Apr (about $290 with a heat pump, $358 with gas). Sunshine peaks in Jun at 8.3 kWh/m²/day (NASA satellite data, 55.4 km grid cell). Highlighted months are swimmable with no heater.
How Gilroy compares with nearby cities
Gilroy ranks 245 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 |
|---|---|---|---|---|
| Morgan Hill, CA | 9 mi | 0 | 7 | $673 |
| Watsonville, CA | 12 mi | 0 | 5 | $804 |
| Hollister, CA | 15 mi | 0 | 6 | $681 |
| Salinas, CA | 22 mi | 0 | 5 | $758 |
| San Jose, CA | 24 mi | 0 | 7 | $550 |
| Scotts Valley, CA | 24 mi | 0 | 9 | $1,510 |