Pool swim season in Lathrop, CA
When can you swim in an outdoor pool in Lathrop, CA?
An unheated pool in Lathrop reaches 78°F in Jul to Sep, about 3 months a year. The air allows up to 7 swimmable months with a heater (Apr to Oct).
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Heater options for a Lathrop pool, side by side
| Option | Months | Swimmable | Energy/yr | All-in/yr |
|---|---|---|---|---|
| No heater | 3 | Jul to Sep | $0 | $0 |
| Solar cover only | 4 | Jun to Sep | $0 | $50 |
| Solar panels + cover | 6 | May to Oct | $0 | $283 |
| Heat pump + cover | 7 | Apr to Oct | $390 | $940 |
| Gas heater + cover | 7 | Apr to Oct | $516 | $941 |
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 Lathrop
Solar panels + cover: 6 of 7 possible months for about $283 a year all-in, which works out near $94 for each month it adds.
Before you pay for any heater, buy a solar cover: on its own it adds 1 month 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: Stockton Airport, 7.5 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
Lathrop 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 | 57° | 48° | 2.4 | 47° | 53° | – | – |
| Feb | 63° | 52° | 3.5 | 51° | 57° | – | – |
| Mar | 69° | 56° | 4.8 | 56° | 62° | – | – |
| Apr | 75° | 61° | 6.2 | 62° | 68° | $241 | $309 |
| May | 83° | 68° | 7.5 | 69° | 75° | $95 | $133 |
| Jun | 90° | 74° | 8.3 | 76° | 82° | – | – |
| Jul | 95° | 78° | 8.2 | 81° | 87° | – | – |
| Aug | 94° | 77° | 7.4 | 82° | 88° | – | – |
| Sep | 90° | 74° | 6.0 | 79° | 85° | – | – |
| Oct | 80° | 66° | 4.4 | 71° | 77° | $54 | $74 |
| Nov | 67° | 55° | 2.9 | 60° | 66° | – | – |
| Dec | 57° | 48° | 2.2 | 50° | 56° | – | – |
Heating costs most in Apr (about $241 with a heat pump, $309 with gas). Sunshine peaks in Jun at 8.3 kWh/m²/day (NASA satellite data, 37.9 km grid cell). Highlighted months are swimmable with no heater.
How Lathrop compares with nearby cities
Lathrop ranks 107 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 |
|---|---|---|---|---|
| Manteca, CA | 5 mi | 3 | 7 | $390 |
| Tracy, CA | 9 mi | 2 | 7 | $522 |
| Ripon, CA | 11 mi | 3 | 7 | $390 |
| Stockton, CA | 12 mi | 3 | 8 | $671 |
| Modesto, CA | 21 mi | 3 | 7 | $385 |
| Riverbank, CA | 21 mi | 3 | 7 | $381 |