Pool swim season in Helena, MT
Swim season in Helena without a heater, and with one
An unheated pool in Helena 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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What each heater buys you in Helena
| 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 | 3 | Jul to Sep | $0 | $283 |
| Heat pump + cover | 4 | Jun to Sep | $223 | $773 |
| Gas heater + cover | 4 | Jun to Sep | $273 | $698 |
For a 450 sq ft pool held at 80°F, at MT prices of 14.1¢/kWh electricity and $9/Mcf gas. All-in spreads the purchase over the equipment's life.
The cheapest way to the full season in Helena
Solar panels + cover: 3 of 4 possible months for about $283 a year all-in, which works out near $94 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: Helena Airport, 1.5 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
Helena 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° | 23° | 1.5 | 22° | 28° | – | – |
| Feb | 37° | 27° | 2.5 | 25° | 31° | – | – |
| Mar | 48° | 36° | 3.7 | 32° | 38° | – | – |
| Apr | 57° | 45° | 4.8 | 42° | 48° | – | – |
| May | 66° | 54° | 5.7 | 52° | 58° | – | – |
| Jun | 75° | 62° | 6.5 | 61° | 67° | $109 | $132 |
| Jul | 86° | 71° | 7.3 | 70° | 76° | $27 | $37 |
| Aug | 85° | 69° | 6.0 | 73° | 79° | $10 | $13 |
| Sep | 73° | 59° | 4.5 | 65° | 71° | $77 | $91 |
| Oct | 58° | 46° | 2.8 | 52° | 58° | – | – |
| Nov | 43° | 33° | 1.6 | 38° | 44° | – | – |
| Dec | 33° | 23° | 1.2 | 26° | 32° | – | – |
Heating costs most in Jun (about $109 with a heat pump, $132 with gas). Sunshine peaks in Jul at 7.3 kWh/m²/day (NASA satellite data, 38.3 km grid cell). Highlighted months are swimmable with no heater.
How Helena compares with nearby cities
Helena ranks 2 of 8 Montana cities for unheated swim months, and no nearby city gets a longer unheated season.
| City | Distance | Unheated months | Heat pump months | Heat pump $/yr |
|---|---|---|---|---|
| Butte-Silver Bow, MT | 57 mi | 0 | 3 | $329 |
| Belgrade, MT | 69 mi | 0 | 4 | $329 |
| Great Falls, MT | 71 mi | 0 | 4 | $220 |
| Bozeman, MT | 78 mi | 0 | 4 | $336 |
| Missoula, MT | 97 mi | 0 | 4 | $269 |
| Kalispell, MT | 156 mi | 0 | 4 | $410 |