Unheated pool temperatures are essentially the average of the nighttime low and daytime high ambient temperatures. It’s well known, and not surprising, that swimming pool temperatures in Southwest Florida closely track the surface temperature of the Gulf of Mexico. The near-shore gulf temperature fits the same pattern. At times, unheated pools can lag large temperature swings, but for the most part, this is the way we can reliably track how warm or cool unheated pools are throughout the year.
This year has been unusually cool through mid-March. While daytime temperatures are mostly normal, nighttime lows have been unseasonably low. This really draws the heat out of pools, regardless of heat source.
Solar pool heaters are weather dependent. On cloudy days you won’t get the heating performance that you get on sunny days. Sunny days are when people are most likely to use their pools, so everything lines up and works out pretty well. But when we get cold snaps, swimming pools can feel quite cool because relative to the outside temperature, they aren’t as warm.
This is true of all heat sources to an extent. Electric heat pumps work less efficiently and slower when temperatures are lower. Gas heaters can heat pools up quickly, but if it’s cool out the pool is cooling at the same time as it is heating. And if it’s cool at night when the pool pump and any heater is off, the pool temperature can drop quickly. Then you start the next day over again, attempting to heat the pool.
Running any pool heater is like running and air conditioner with the doors open. It’s not a great idea, but if you want to use your pool there isn’t a great alternative. Covering your pool helps quite a bit, since most heat is lost at the pool surface and through the process of evaporation.
So if you are going to “run your air conditioner with the door open” you probably should consider a heat source that doesn’t cost anything. That’s why solar-heated pools are so popular. You can reach temperatures of 8-12 degrees Fahrenheit above an unheated pool most of the time. While this may not be completely adequate 12 months of the year, it is much, much better than an unheated pool. And it’s free after the initial investment.
So while solar pool heating is weather dependent, so are all heat sources. During unseasonably cool weather you shouldn’t expect to use your pool every single day, or shouldn’t expect it to be like bathwater. Some visitors and new residents of Southwest Florida come here with the misconception that swimming pools are enjoyed year-round here. While that is mostly the case, when we get cold snaps and unseasonably cold weather, pools can be less than desirable in terms of temperature. That’s the reality. Even an electric heat pump can’t work effectively on the coldest days, and all the heat gained during the day can easily be lost at night.
Solar pool heating dramatically increases the number of days per year that you can use your pool and increases enjoyment tremendously. That’s why they are so popular here! But keep in mind it is weather-dependent like all pool heaters in one way or another.