Pool swim season in Duarte, CA
When can you swim in an outdoor pool in Duarte, CA?
An unheated pool in Duarte reaches 78°F in Aug, about 1 month a year. The air allows up to 5 swimmable months with a heater (Jun to Oct).
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What each heater buys you in Duarte
| Option | Months | Swimmable | Energy/yr | All-in/yr |
|---|---|---|---|---|
| No heater | 1 | Aug | $0 | $0 |
| Solar cover only | 3 | Jul to Sep | $0 | $50 |
| Solar panels + cover | 5 | Jun to Oct | $0 | $283 |
| Heat pump + cover | 5 | Jun to Oct | $218 | $768 |
| Gas heater + cover | 5 | Jun to Oct | $294 | $719 |
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 Duarte
Solar panels + cover: 5 of 5 possible months for about $283 a year all-in, which works out near $71 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 gas as well as a heat pump: once the purchase price is counted, gas comes out cheaper all-in here (heat pump or gas).
Weather station: Mt Wilson Cbs, 8.4 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
Duarte 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 | 56° | 47° | 3.3 | 47° | 53° | – | – |
| Feb | 55° | 46° | 4.2 | 48° | 54° | – | – |
| Mar | 59° | 49° | 5.6 | 50° | 56° | – | – |
| Apr | 63° | 52° | 6.9 | 55° | 61° | – | – |
| May | 70° | 59° | 7.8 | 60° | 66° | – | – |
| Jun | 79° | 68° | 8.4 | 69° | 75° | $93 | $132 |
| Jul | 85° | 74° | 7.9 | 76° | 82° | – | – |
| Aug | 85° | 75° | 7.4 | 79° | 85° | – | – |
| Sep | 81° | 70° | 6.3 | 76° | 82° | – | – |
| Oct | 72° | 62° | 4.9 | 68° | 74° | $125 | $162 |
| Nov | 63° | 53° | 3.7 | 58° | 64° | – | – |
| Dec | 55° | 46° | 2.9 | 50° | 56° | – | – |
Heating costs most in Oct (about $125 with a heat pump, $162 with gas). Sunshine peaks in Jun at 8.4 kWh/m²/day (NASA satellite data, 56.0 km grid cell). Highlighted months are swimmable with no heater.
How Duarte compares with nearby cities
Duarte ranks 191 of 376 California cities for unheated swim months; Azusa, Arcadia, Baldwin Park nearby get a longer season without a heater.
| City | Distance | Unheated months | Heat pump months | Heat pump $/yr |
|---|---|---|---|---|
| Monrovia, CA | 2 mi | 1 | 5 | $218 |
| Azusa, CA | 3 mi | 3 | 9 | $758 |
| Arcadia, CA | 5 mi | 3 | 9 | $650 |
| Baldwin Park, CA | 6 mi | 3 | 9 | $631 |
| Sierra Madre, CA | 6 mi | 1 | 5 | $227 |
| Glendora, CA | 6 mi | 3 | 9 | $758 |