Pool swim season in Ann Arbor, MI
Swim season in Ann Arbor without a heater, and with one
An unheated pool in Ann Arbor never reaches 78°F in a normal year. It peaks around 73°F in Aug. The air allows up to 5 swimmable months with a heater (May to Sep).
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Heater options for a Ann Arbor pool, side by side
| Option | Months | Swimmable | Energy/yr | All-in/yr |
|---|---|---|---|---|
| No heater | 0 | no month | $0 | $0 |
| Solar cover only | 2 | Jul to Aug | $0 | $50 |
| Solar panels + cover | 4 | Jun to Sep | $0 | $283 |
| Heat pump + cover | 5 | May to Sep | $482 | $1,032 |
| Gas heater + cover | 5 | May to Sep | $463 | $888 |
For a 450 sq ft pool held at 80°F, at MI prices of 21.7¢/kWh electricity and $11/Mcf gas. All-in spreads the purchase over the equipment's life.
The cheapest way to the full season in Ann Arbor
Solar panels + cover: 4 of 5 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 2 months 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: Ann Arbor SE, 3.1 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
Ann Arbor 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 | 32° | 24° | 1.6 | 25° | 31° | – | – |
| Feb | 35° | 26° | 2.4 | 24° | 30° | – | – |
| Mar | 45° | 35° | 3.5 | 31° | 37° | – | – |
| Apr | 58° | 46° | 4.7 | 42° | 48° | – | – |
| May | 70° | 58° | 5.4 | 55° | 61° | $270 | $247 |
| Jun | 80° | 68° | 6.2 | 66° | 72° | $98 | $102 |
| Jul | 84° | 72° | 6.2 | 73° | 79° | $14 | $16 |
| Aug | 82° | 70° | 5.3 | 73° | 79° | $13 | $13 |
| Sep | 75° | 62° | 4.3 | 67° | 73° | $87 | $85 |
| Oct | 62° | 51° | 2.8 | 56° | 62° | – | – |
| Nov | 48° | 39° | 1.8 | 43° | 49° | – | – |
| Dec | 36° | 29° | 1.2 | 32° | 38° | – | – |
Heating costs most in May (about $270 with a heat pump, $247 with gas). Sunshine peaks in Jul at 6.2 kWh/m²/day (NASA satellite data, 31.3 km grid cell). Highlighted months are swimmable with no heater.
How Ann Arbor compares with nearby cities
Ann Arbor ranks 62 of 90 Michigan cities for unheated swim months, and no nearby city gets a longer unheated season.
| City | Distance | Unheated months | Heat pump months | Heat pump $/yr |
|---|---|---|---|---|
| Ypsilanti, MI | 6 mi | 0 | 5 | $482 |
| South Lyon, MI | 13 mi | 0 | 4 | $279 |
| Wayne, MI | 18 mi | 0 | 5 | $347 |
| Westland, MI | 18 mi | 0 | 5 | $347 |
| Novi, MI | 19 mi | 0 | 4 | $224 |
| Romulus, MI | 19 mi | 0 | 5 | $347 |