Pool swim season in Johnstown, CO
When can you swim in an outdoor pool in Johnstown, CO?
An unheated pool in Johnstown never reaches 78°F in a normal year. It peaks around 74°F in Aug. The air allows up to 5 swimmable months with a heater (May to Sep).
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What each heater buys you in Johnstown
| 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 | $377 | $927 |
| Gas heater + cover | 5 | May to Sep | $464 | $889 |
For a 450 sq ft pool held at 80°F, at CO prices of 16.8¢/kWh electricity and $11/Mcf gas. All-in spreads the purchase over the equipment's life.
The cheapest way to the full season in Johnstown
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: Loveland 2N, 12.7 mi away (NOAA 1991–2020 normals). Water temperature is estimated from air and sunshine, not measured.
Johnstown 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 | 44° | 28° | 2.4 | 28° | 34° | – | – |
| Feb | 46° | 31° | 3.3 | 30° | 36° | – | – |
| Mar | 56° | 40° | 4.6 | 37° | 43° | – | – |
| Apr | 62° | 47° | 5.6 | 46° | 52° | – | – |
| May | 71° | 55° | 6.3 | 54° | 60° | $219 | $255 |
| Jun | 83° | 66° | 7.3 | 65° | 71° | $87 | $117 |
| Jul | 89° | 72° | 7.0 | 73° | 79° | $9 | $13 |
| Aug | 87° | 70° | 6.2 | 74° | 80° | – | – |
| Sep | 79° | 62° | 5.2 | 68° | 74° | $62 | $79 |
| Oct | 65° | 49° | 3.7 | 56° | 62° | – | – |
| Nov | 53° | 37° | 2.7 | 43° | 49° | – | – |
| Dec | 44° | 29° | 2.1 | 32° | 38° | – | – |
Heating costs most in May (about $219 with a heat pump, $255 with gas). Sunshine peaks in Jun at 7.3 kWh/m²/day (NASA satellite data, 40.9 km grid cell). Highlighted months are swimmable with no heater.
How Johnstown compares with nearby cities
Johnstown ranks 44 of 53 Colorado cities for unheated swim months, and no nearby city gets a longer unheated season.
| City | Distance | Unheated months | Heat pump months | Heat pump $/yr |
|---|---|---|---|---|
| Berthoud, CO | 3 mi | 0 | 5 | $318 |
| Evans, CO | 9 mi | 0 | 5 | $232 |
| Greeley, CO | 10 mi | 0 | 5 | $232 |
| Firestone, CO | 11 mi | 0 | 5 | $318 |
| Loveland, CO | 11 mi | 0 | 5 | $393 |
| Windsor, CO | 12 mi | 0 | 4 | $138 |