If you own a gas-powered pool heater, you might wonder if it functions similar to the way home heating or AC does, where it’s often suggested to keep it at a reasonable minimum temperature at all times rather than shutting it off completely.
In addition to your heater itself, you can of course also rely on the sun’s rays and utilize other effective water-warmers such as a solar blanket so a pool heater isn’t the only choice to warm the water.
It’s not advisable to keep your pool heater on all night due to the high energy costs you’ll experience. You’re better off investing in a quality solar blanket that you cover the pool with to retain heat overnight and reduce evaporation during the day. Use the heater and sun’s rays in the morning before pool use.
Plus as we’ll find out below, it’s actually water evaporation that leads to the largest loss of heat in a pool so you need to prevent this from happening more than you need to actively heat a pool to keep the water warm.
Can you leave a pool heater on overnight?
While you can leave a pool heater on overnight to keep the water warm, it’s not advisable. You’re not using the pool overnight so keeping it heated is a waste of money. Plus it means you’ll need to run the pump constantly too which also uses energy.
Your best bet is to purchase a quality solar blanket that covers the entire pool surface and use it each night when you’re done swimming for the day. A solar blanket can significantly reduce water evaporation while helping to retain heat in the pool overnight when the air temperature goes down.
Then the next day, keep the solar blanket on until you’re ready to swim and turn the pool heater on several hours before pool use if desired. You can keep the pool heater running while using the pool if you like and then turn it off when you’ve finished swimming. Then use the solar blanket again at night.
Remember to set the thermostat high enough that it reaches a temperature that you’re happy with. If you set it too low, the heat will shut off just like your AC or furnace does inside your house.
And in case you were wondering, you can heat your salt water pool using the same heating methods as a regularly chlorinated pool.
How effective are solar pool covers?
Water evaporation results in the single largest loss of heat in a pool. Evaporation can be responsible for 50% – 70% of heat loss in a pool depending on how much direct sun you receive. While cool night time temperatures assist in the process, water evaporation is the leading cause of heat loss and it’s easy to see why. Using a solar cover can reduce water evaporation by up to 95%.
Water on the surface of the pool quickly evaporates from the hot direct rays of the sun. It’s the warmest water in the pool and is the first to suffer from the effects of evaporation resulting in massive heat loss from the pool.
How much can a solar blanket help to not only reduce water evaporation but thus heat loss and energy usage? According to the Energy Department, it’s significant:
Pool covers minimize evaporation from both outdoor and indoor pools. Covering a pool when it is not in use is the single most effective means of reducing pool heating costs. Savings of 50%–70% are possible.
Energy.gov
Putting a solar blanket on your pool each evening and during the day when it’s not in use is akin to keeping your doors and windows shut in your home while the air conditioner is running: It just makes sense.
Just don’t leave the solar blanket on for more than a day or so at a time. With very hot days and significant direct sun beating down on the cover, algae can form if you don’t uncover the pool soon enough.
How efficient are gas-powered pool heaters?
The most efficient gas pool heaters are rated at between 89% and 95% efficiency. As with other gas-powered appliances such as a furnace, natural gas pool heaters are rated according to their fuel efficiency based on British Thermal Units (BTUs) output. Many manufacturers state the percentage efficiency right on the nameplate of their pool heaters.
A pool heater with 89% efficiency means that 89% of the fuel burned produces heat and the remaining 11% is effectively lost in the heating process.
Looking at it another way, for every $100 spent on heating your pool the heater will produce $89 worth of useful heat. Depending on how much you use your pool heater and the local gas rates, a bill of $200 – $400 per month during the pool season is not uncommon. A cost of around $7 per hour of heater usage is about average.
Gas pool heaters typical range from 75,000 BTUs to 450,000 BTUs of output and the more output the faster the heating but the greater the energy costs.
The higher the efficiency rating, the more useful heat is produced for every dollar spent on fuel.
Does liquid solar cover prevent heat loss in a pool?
You may have heard of liquid solar covers which are chemicals that are added to the pool water to retain heat. Often referred to as a liquid solar blanket, the products are typically made with a combination of chemicals that are lighter than water and thus float and remain on the surface of the pool.
They are purported to offer benefits such as heat retention and water evaporation reduction.
Some products can be squirted into the water whereas others are added slowly by way of a floating fish or other device that releases the chemical in the water over time. More sophisticated systems provide an automatic dosage mechanism to add a prescribed amount to pool water each day.
Do these products actually work or are they a waste of money?
Heatsavr is one of the more well known brands of liquid solar covers and has produced its own research for both indoor and outdoor pools that you can view by clicking here. The results show that energy savings ranged from 15% to 55% when utilizing the Heatsavr product.
Savings were achieved in terms of less water evaporation and lost heat overnight resulting in lower energy and maintenance costs. The product basically acts like a sunscreen for the pool water or similar to putting a lid on a coffee cup to retain the heat.
Key determinants for heating your pool
Your ability to heat your swimming pool relies on a number of factors:
- How much direct sun you get each day i.e. more sun = more heat but it also means higher water evaporation.
- Whether or not your pool is shaded and shielded from the warm rays of the sun.
- Whether or not you use a solar blanket to retain heat in the pool overnight and protect against evaporation during the day.
- The water volume in your pool and depth of the deepest area i.e. deeper water takes longer to heat.
- The output in BTUs of your pool heater i.e. the more powerful your heater, the quicker it will heat the water.
- How many hours per day you run your pump i.e. a pool heater only operates when the pump is running.
How to cost effectively use your pool heater
A good rule of thumb is that a pool heater can heat the water around 1 degree per hour. Your pool heater can remain on but not actually be running as it depends on how high you have the thermostat set. As with any thermostat, once it hits the set temperature, it will shut off.
Plus you can only heat the pool when the pump is running so if the pump is shut off, the heater isn’t operating.
But if you keep the pump running 24/7 and crank the thermostat up, you could potentially run the heater constantly. As we’ve seen above though, this isn’t the best strategy since it doesn’t account for heat loss through evaporation.
With that in mind, plan ahead when you’re going to use the pool and turn the heater on several hours beforehand. Most pool heaters are sized to heat the pool around 1 degree per hour but a more powerful heater may achieve up to 2 degrees per hour.
Use your pool heater in conjunction with a solar blanket at night and when the pool isn’t in use during the day. This goes a long way to keep your pool water at a reasonably warm temperature for you and anyone swimming.
Summary
The most cost effective way to heat your pool is to use a solar blanket in conjunction with the warm sun heating the water during the day.
Using your pool heater costs money but also speeds up the heating process.
A typical range to set your pool heater is in the range of 78°F and 82°F (26°C and 28°C) which should keep most swimmers happy. You can adjust down or up of course as desired but the warmer the pool, the higher your heating costs if you use a gas heater.
Keep in mind too that you don’t have to specifically choose a gas-powered pool heater as electric and solar powered units are now commonly available, too.
Click here to learn more about other pool heating possibilities but don’t forget about the benefits of a solar blanket.