Pool swim season in Mount Vernon, WA
Mount Vernon, WA: how long the pool season really is
An unheated pool in Mount Vernon never reaches 78°F in a normal year. It peaks around 66°F in Aug. The air allows up to 2 swimmable months with a heater (Jul to Aug).
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What each heater buys you in Mount Vernon
| 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 | 2 | Jul to Aug | $141 | $691 |
| Gas heater + cover | 2 | Jul to Aug | $340 | $765 |
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 Mount Vernon
Solar panels + cover: 2 of 2 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: Mt Vernon 3 WNW, 3.8 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
Mount Vernon 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° | 41° | 1.0 | 39° | 45° | – | – |
| Feb | 50° | 42° | 1.9 | 41° | 47° | – | – |
| Mar | 54° | 46° | 2.9 | 44° | 50° | – | – |
| Apr | 58° | 50° | 4.3 | 49° | 55° | – | – |
| May | 65° | 56° | 5.5 | 55° | 61° | – | – |
| Jun | 69° | 60° | 6.0 | 61° | 67° | – | – |
| Jul | 73° | 63° | 6.5 | 65° | 71° | $76 | $182 |
| Aug | 75° | 64° | 5.5 | 66° | 72° | $65 | $158 |
| Sep | 69° | 59° | 3.9 | 62° | 68° | – | – |
| Oct | 59° | 51° | 2.2 | 54° | 60° | – | – |
| Nov | 51° | 45° | 1.1 | 46° | 52° | – | – |
| Dec | 46° | 41° | 0.8 | 41° | 47° | – | – |
Heating costs most in Jul (about $76 with a heat pump, $182 with gas). Sunshine peaks in Jul at 6.5 kWh/m²/day (NASA satellite data, 16.7 km grid cell). Highlighted months are swimmable with no heater.
How Mount Vernon compares with nearby cities
Mount Vernon ranks 81 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 |
|---|---|---|---|---|
| Burlington, WA | 3 mi | 0 | 2 | $141 |
| Sedro-Woolley, WA | 7 mi | 0 | 2 | $138 |
| Anacortes, WA | 15 mi | 0 | 3 | $215 |
| Oak Harbor, WA | 17 mi | 0 | 0 | $0 |
| Arlington, WA | 19 mi | 0 | 4 | $426 |
| Bellingham, WA | 24 mi | 0 | 2 | $129 |