Pool swim season in Honolulu, HI
When can you swim in an outdoor pool in Honolulu, HI?
An unheated pool in Honolulu reaches 78°F in Aug to Sep, about 2 months a year. The air allows up to 12 swimmable months with a heater (all year).
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Heater options for a Honolulu pool, side by side
| Option | Months | Swimmable | Energy/yr | All-in/yr |
|---|---|---|---|---|
| No heater | 2 | Aug to Sep | $0 | $0 |
| Solar cover only | 10 | Mar to Dec | $0 | $50 |
| Solar panels + cover | 12 | all year | $0 | $283 |
| Heat pump + cover | 12 | all year | $215 | $765 |
| Gas heater + cover | 12 | all year | $520 | $945 |
For a 450 sq ft pool held at 80°F, at HI prices of 46.4¢/kWh electricity and $52/Mcf gas. All-in spreads the purchase over the equipment's life.
The cheapest way to the full season in Honolulu
Solar panels + cover: 12 of 12 possible months for about $283 a year all-in, which works out near $28 for each month it adds.
Before you pay for any heater, buy a solar cover: on its own it adds 8 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: Manoa Lyon Arbo 785.2, 3 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
Honolulu 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 | 76° | 70° | 4.3 | 72° | 78° | $63 | $152 |
| Feb | 76° | 70° | 4.9 | 72° | 78° | $64 | $155 |
| Mar | 76° | 70° | 5.5 | 72° | 78° | $46 | $111 |
| Apr | 76° | 71° | 6.3 | 74° | 80° | $12 | $28 |
| May | 78° | 72° | 6.8 | 75° | 81° | – | – |
| Jun | 78° | 73° | 7.1 | 77° | 83° | – | – |
| Jul | 79° | 74° | 7.0 | 78° | 84° | – | – |
| Aug | 80° | 75° | 6.7 | 79° | 85° | – | – |
| Sep | 81° | 75° | 6.2 | 79° | 85° | – | – |
| Oct | 80° | 75° | 5.2 | 77° | 83° | – | – |
| Nov | 78° | 73° | 4.4 | 75° | 81° | – | – |
| Dec | 76° | 71° | 3.9 | 73° | 79° | $30 | $74 |
Heating costs most in Feb (about $64 with a heat pump, $155 with gas). Sunshine peaks in Jun at 7.1 kWh/m²/day (NASA satellite data, 40.9 km grid cell). Highlighted months are swimmable with no heater.
How Honolulu compares with nearby cities
Honolulu ranks 1 of 1 Hawaii cities for unheated swim months, and no nearby city gets a longer unheated season.
| City | Distance | Unheated months | Heat pump months | Heat pump $/yr |
|---|---|---|---|---|
| San Francisco, CA | 2361 mi | 0 | 0 | $0 |
| Fortuna, CA | 2377 mi | 0 | 3 | $560 |
| Eureka, CA | 2382 mi | 0 | 0 | $0 |
| Ukiah, CA | 2385 mi | 0 | 6 | $467 |
| Half Moon Bay, CA | 2386 mi | 0 | 0 | $0 |
| Pacifica, CA | 2387 mi | 0 | 3 | $588 |