Pool swim season in Sammamish, WA
When can you swim in an outdoor pool in Sammamish, WA?
An unheated pool in Sammamish never reaches 78°F in a normal year. It peaks around 68°F in Aug. The air allows up to 3 swimmable months with a heater (Jul to Sep).
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What each heater buys you in Sammamish
| Option | Months | Swimmable | Energy/yr | All-in/yr |
|---|---|---|---|---|
| No heater | 0 | no month | $0 | $0 |
| Solar cover only | 0 | no month | $0 | $50 |
| Solar panels + cover | 2 | Jul to Aug | $0 | $283 |
| Heat pump + cover | 3 | Jul to Sep | $218 | $768 |
| Gas heater + cover | 3 | Jul to Sep | $521 | $946 |
For a 450 sq ft pool held at 80°F, at WA prices of 14.4¢/kWh electricity and $18/Mcf gas. All-in spreads the purchase over the equipment's life.
The cheapest way to the full season in Sammamish
Solar panels + cover: 2 of 3 possible months for about $283 a year all-in, which works out near $142 for each month it adds.
A solar cover alone adds no swim months here, so if you want a longer season you need a heater (why); still use one at night to hold the heat you pay for. 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: Snoqualmie Falls, 10.1 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
Sammamish 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 | 46° | 41° | 1.0 | 39° | 45° | – | – |
| Feb | 50° | 42° | 1.9 | 41° | 47° | – | – |
| Mar | 54° | 45° | 2.8 | 44° | 50° | – | – |
| Apr | 59° | 50° | 4.2 | 49° | 55° | – | – |
| May | 64° | 55° | 5.2 | 55° | 61° | – | – |
| Jun | 69° | 60° | 5.7 | 60° | 66° | – | – |
| Jul | 76° | 65° | 6.3 | 66° | 72° | $69 | $170 |
| Aug | 77° | 65° | 5.4 | 68° | 74° | $54 | $134 |
| Sep | 70° | 60° | 3.9 | 63° | 69° | $95 | $217 |
| Oct | 60° | 52° | 2.3 | 55° | 61° | – | – |
| Nov | 51° | 45° | 1.2 | 46° | 52° | – | – |
| Dec | 46° | 41° | 0.9 | 41° | 47° | – | – |
Heating costs most in Sep (about $95 with a heat pump, $217 with gas). Sunshine peaks in Jul at 6.3 kWh/m²/day (NASA satellite data, 36.2 km grid cell). Highlighted months are swimmable with no heater.
How Sammamish compares with nearby cities
Sammamish ranks 60 of 91 Washington cities for unheated swim months, and no nearby city gets a longer unheated season.
| City | Distance | Unheated months | Heat pump months | Heat pump $/yr |
|---|---|---|---|---|
| Issaquah, WA | 3 mi | 0 | 4 | $249 |
| Bellevue, WA | 6 mi | 0 | 4 | $249 |
| Redmond, WA | 7 mi | 0 | 4 | $272 |
| Newcastle, WA | 7 mi | 0 | 4 | $249 |
| Snoqualmie, WA | 9 mi | 0 | 3 | $205 |
| Mercer Island, WA | 9 mi | 0 | 4 | $240 |