Pool swim season in Shoreline, WA
When can you swim in an outdoor pool in Shoreline, WA?
An unheated pool in Shoreline never reaches 78°F in a normal year. It peaks around 69°F in Aug. The air allows up to 4 swimmable months with a heater (Jun to Sep).
- J
- F
- M
- A
- M
- J
- J
- A
- S
- O
- N
- D
Heater options for a Shoreline pool, side by side
| 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 | 4 | Jun to Sep | $272 | $822 |
| Gas heater + cover | 4 | Jun to Sep | $654 | $1,079 |
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 Shoreline
Heat pump + cover: 4 of 4 possible months for about $822 a year all-in, which works out near $206 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: Seattle Sand Pt NWS Office, 6.4 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
Shoreline 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 | 47° | 42° | 1.0 | 40° | 46° | – | – |
| Feb | 50° | 43° | 1.9 | 42° | 48° | – | – |
| Mar | 54° | 47° | 2.8 | 45° | 51° | – | – |
| Apr | 59° | 51° | 4.2 | 50° | 56° | – | – |
| May | 65° | 57° | 5.2 | 56° | 62° | – | – |
| Jun | 70° | 61° | 5.7 | 62° | 68° | $106 | $248 |
| Jul | 77° | 67° | 6.3 | 67° | 73° | $55 | $137 |
| Aug | 77° | 67° | 5.4 | 69° | 75° | $39 | $98 |
| Sep | 71° | 62° | 3.9 | 66° | 72° | $72 | $171 |
| Oct | 61° | 54° | 2.3 | 57° | 63° | – | – |
| Nov | 52° | 46° | 1.2 | 48° | 54° | – | – |
| Dec | 47° | 42° | 0.9 | 42° | 48° | – | – |
Heating costs most in Jun (about $106 with a heat pump, $248 with gas). Sunshine peaks in Jul at 6.3 kWh/m²/day (NASA satellite data, 30.8 km grid cell). Highlighted months are swimmable with no heater.
How Shoreline compares with nearby cities
Shoreline ranks 39 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 |
|---|---|---|---|---|
| Lake Forest Park, WA | 3 mi | 0 | 4 | $272 |
| Mountlake Terrace, WA | 3 mi | 0 | 4 | $272 |
| Edmonds, WA | 4 mi | 0 | 2 | $145 |
| Kenmore, WA | 5 mi | 0 | 4 | $272 |
| Lynnwood, WA | 5 mi | 0 | 2 | $145 |
| Bothell, WA | 7 mi | 0 | 4 | $272 |