Pool swim season in San Marcos, CA
San Marcos, CA: how long the pool season really is
An unheated pool in San Marcos reaches 78°F in Aug to Sep, about 2 months a year. The air allows up to 9 swimmable months with a heater (Mar to Nov).
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Heater options for a San Marcos pool, side by side
| Option | Months | Swimmable | Energy/yr | All-in/yr |
|---|---|---|---|---|
| No heater | 2 | Aug to Sep | $0 | $0 |
| Solar cover only | 5 | Jun to Oct | $0 | $50 |
| Solar panels + cover | 7 | Apr to Oct | $0 | $283 |
| Heat pump + cover | 9 | Mar to Nov | $711 | $1,261 |
| Gas heater + cover | 9 | Mar to Nov | $931 | $1,356 |
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 Marcos
Heat pump + cover: 9 of 9 possible months for about $1,261 a year all-in, which works out near $180 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: Escondido #2, 4.7 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
San Marcos 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 | 69° | 57° | 3.2 | 57° | 63° | – | – |
| Feb | 69° | 57° | 4.1 | 58° | 64° | – | – |
| Mar | 71° | 60° | 5.4 | 61° | 67° | $262 | $332 |
| Apr | 74° | 63° | 6.5 | 65° | 71° | $175 | $231 |
| May | 77° | 67° | 6.9 | 69° | 75° | $97 | $134 |
| Jun | 82° | 71° | 7.3 | 73° | 79° | $15 | $22 |
| Jul | 87° | 76° | 7.4 | 78° | 84° | – | – |
| Aug | 89° | 77° | 7.1 | 81° | 87° | – | – |
| Sep | 87° | 75° | 6.0 | 79° | 85° | – | – |
| Oct | 81° | 69° | 4.6 | 74° | 80° | $6 | $9 |
| Nov | 75° | 62° | 3.6 | 66° | 72° | $156 | $203 |
| Dec | 68° | 56° | 2.9 | 59° | 65° | – | – |
Heating costs most in Mar (about $262 with a heat pump, $332 with gas). Sunshine peaks in Jul at 7.4 kWh/m²/day (NASA satellite data, 51.1 km grid cell). Highlighted months are swimmable with no heater.
How San Marcos compares with nearby cities
San Marcos ranks 152 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 |
|---|---|---|---|---|
| Escondido, CA | 6 mi | 2 | 9 | $711 |
| Vista, CA | 6 mi | 0 | 7 | $552 |
| Carlsbad, CA | 7 mi | 0 | 4 | $147 |
| Encinitas, CA | 8 mi | 0 | 4 | $147 |
| Oceanside, CA | 10 mi | 0 | 6 | $571 |
| Solana Beach, CA | 11 mi | 0 | 4 | $203 |