Pool swim season in Grafton, WI
Grafton, WI: how long the pool season really is
An unheated pool in Grafton never reaches 78°F in a normal year. It peaks around 73°F in Aug. The air allows up to 4 swimmable months with a heater (Jun to Sep).
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Heater options for a Grafton pool, side by side
| Option | Months | Swimmable | Energy/yr | All-in/yr |
|---|---|---|---|---|
| No heater | 0 | no month | $0 | $0 |
| Solar cover only | 1 | Aug | $0 | $50 |
| Solar panels + cover | 4 | Jun to Sep | $0 | $283 |
| Heat pump + cover | 4 | Jun to Sep | $213 | $763 |
| Gas heater + cover | 4 | Jun to Sep | $244 | $669 |
For a 450 sq ft pool held at 80°F, at WI prices of 19.1¢/kWh electricity and $11/Mcf gas. All-in spreads the purchase over the equipment's life.
The cheapest way to the full season in Grafton
Solar panels + cover: 4 of 4 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 1 month 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: Grafton Water Treatment Plant, 1 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
Grafton 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 | 30° | 24° | 1.4 | 24° | 30° | – | – |
| Feb | 33° | 26° | 2.3 | 24° | 30° | – | – |
| Mar | 43° | 35° | 3.5 | 31° | 37° | – | – |
| Apr | 54° | 45° | 4.6 | 41° | 47° | – | – |
| May | 66° | 56° | 5.4 | 53° | 59° | – | – |
| Jun | 76° | 66° | 6.0 | 64° | 70° | $112 | $128 |
| Jul | 81° | 72° | 6.1 | 72° | 78° | $23 | $28 |
| Aug | 80° | 70° | 5.2 | 73° | 79° | $9 | $11 |
| Sep | 73° | 63° | 4.2 | 68° | 74° | $69 | $77 |
| Oct | 61° | 52° | 2.7 | 57° | 63° | – | – |
| Nov | 46° | 39° | 1.7 | 44° | 50° | – | – |
| Dec | 35° | 28° | 1.2 | 32° | 38° | – | – |
Heating costs most in Jun (about $112 with a heat pump, $128 with gas). Sunshine peaks in Jul at 6.1 kWh/m²/day (NASA satellite data, 41.3 km grid cell). Highlighted months are swimmable with no heater.
How Grafton compares with nearby cities
Grafton ranks 46 of 98 Wisconsin cities for unheated swim months, and no nearby city gets a longer unheated season.
| City | Distance | Unheated months | Heat pump months | Heat pump $/yr |
|---|---|---|---|---|
| Cedarburg, WI | 3 mi | 0 | 4 | $213 |
| Port Washington, WI | 5 mi | 0 | 4 | $283 |
| Mequon, WI | 8 mi | 0 | 4 | $264 |
| Brown Deer, WI | 10 mi | 0 | 4 | $153 |
| Germantown, WI | 11 mi | 0 | 4 | $264 |
| Glendale, WI | 13 mi | 0 | 4 | $153 |