What is the difference between a pool heater and a solar cover?
They solve two different problems, which is why comparing them head to head is a little unfair to both. A pool heater makes heat. Gas, a heat pump, or solar panels feed energy into the water, so a heater can raise the temperature to a number you choose and hold it there whether it is a sunny afternoon or a cool, cloudy evening. That is a job a solar cover simply cannot do. A solar cover keeps heat. It floats on the surface, and its two real jobs are to stop the water from evaporating and to let some sunlight through to warm the top layer. It adds no energy of its own beyond the free sun, so it can only slow the pool's natural cooling and grab a little warmth on a bright day.
The reason a cover matters so much comes down to how pools lose heat. Evaporation is the single biggest way a pool sheds warmth, far ahead of conduction through the walls or radiation to the night sky, and it accelerates on warm, dry, or windy days. Every gallon that evaporates carries a large amount of heat away with it. A solar cover blocks that surface, so it cuts evaporation dramatically, which is why a covered pool holds its temperature overnight while an open one can drop several degrees by morning. The same cover also slows the water and chemical loss from evaporation and blocks some UV, so it stretches your chlorine a bit too.
So the clean way to think about it is this: a heater is the throttle and a cover is the insulation. One adds heat, the other keeps it. That framing is also why they work so well together, and why the smartest money for many pools is not a bigger heater but a cheap cover on the heater you already have. If you are weighing the heater types themselves, our how to heat a pool guide and the gas vs heat pump comparison break those down.
How much warmer will a solar cover make a pool?
A solar cover typically adds about 5 to 10 degrees Fahrenheit when you use it consistently, and the gain is real but slow and weather-dependent. Most of that warmth is not new heat the cover created; it is heat the pool would have lost to evaporation overnight that the cover kept in. That is why the cover has to be on most of the time to do its job. Leave it off for the evenings and you give back the day's gain, and you start each morning cold. Used faithfully, though, a cover can push a mid-season pool from an uncomfortable 74 degrees into the low 80s and extend your swimming season by a few weeks on each end.
The pool heats faster and holds heat better with the cover on, not off. This trips people up because they assume an open pool soaks up more sun. It does gain a little more direct solar during peak afternoon, but that is swamped by the evaporative cooling an open surface suffers the rest of the day and all night. A clear or light blue cover still transmits plenty of sunlight to the water while shutting down evaporation, so on balance you warm up faster and stay warm with it on. The one time to pull it is a scorching midsummer stretch when the pool is already too warm and you want it to breathe.
The honest cons of a solar cover are worth knowing before you count on one. It is bulky and a chore to roll on and off without a reel, it degrades in sunlight and usually needs replacing every 2 to 3 years, and it does nothing on a cloudy day or a cold night when there is no sun to capture. It is also not a safety cover: it will not hold any weight, a child or pet can slip under it and drown, and it is no substitute for a fence, an alarm, or supervision. And you cannot swim with it on, so it lives on a reel by the pool. If leaks are shrinking your season instead of the weather, rule that out with our pool leak guide before spending on heat. For picking a cover, see our best solar pool covers roundup.
When do you actually need a pool heater?
You need a heater when you want a specific temperature on demand, regardless of the weather. A solar cover can nudge a warm-climate pool a few degrees and hold what the sun gives you, but it cannot hit a target, it cannot heat on a cool cloudy day, and it cannot warm the water fast for a weekend party. If you swim in spring and fall, live where nights get cold, keep the pool at a set number for lap swimming or an older swimmer, or simply refuse to gamble comfort on the forecast, that is heater territory.
The three heater types trade speed for running cost. A gas heater (natural gas or propane) heats fastest and works in any weather, which makes it the pick for on-demand and cold-climate use, but it costs the most per hour to run. A heat pump pulls heat from the air, so it costs far less to run and is the efficient choice for holding a temperature all season, but it heats slowly and fades as the air drops below about 50 degrees. Solar panels cost the most to install and depend on sun and roof space, but their running cost is essentially zero. Our solar vs heat pump and gas vs heat pump comparisons walk through which fits which pool.
Whichever you choose, size it to the pool. Heating a body of water is mostly a function of its volume and the temperature rise you want, so start by measuring the pool with the pool volume calculator, then match the heater's output to it. An undersized heater runs forever and never quite catches up; an oversized gas unit heats fast but costs more upfront. Our best pool heaters guide covers real models by type and pool size.
Should you use a solar cover and a heater together?
Yes, and it is the setup that makes the most sense for almost any heated pool. A solar cover on a heated pool is the cheapest performance upgrade you can buy, because it stops the evaporation that would otherwise carry your purchased heat straight out of the water. Industry and utility estimates put the savings from covering a heated pool at roughly 50 to 70 percent of the heating cost, which means a $30 cover can pay for itself in a single month of gas bills. The heater does the heavy lifting of reaching the temperature you want; the cover keeps you from paying to reheat it every night.
You can absolutely run the heater with the cover on, and you should. The two do not conflict: the heater warms the water while the cover keeps that warmth in, so the heater cycles on less often and runs shorter to hold the same temperature. The only thing to watch is that a cover traps heat well, so on a warm day a pool can climb past your set point faster than you expect; just check the temperature and pull the cover if it overshoots. There is no harm to the heater from running it under a cover.
So the buying order for most people is clear. Get the cover first: it is under a couple hundred dollars, it adds 5 to 10 degrees on its own in a sunny climate, and it slashes the running cost of any heater you add later. Then add a heater when the cover alone cannot reach or hold the temperature you want, which is common the moment you try to swim outside the warm months. The mistake is buying a heater and skipping the cover, because you then pay full price to reheat the pool every single night. For a rundown of every cover type, not just solar, see our best pool covers guide.
Pool Heater wins on
- +Dependable, on-demand heat that works in any weather, day or night.
- +Holds a set temperature you choose, and gas heats fast enough for a same-day swim.
- +Extends the season at both ends and heats a pool a solar cover alone never could.
Solar Cover wins on
- +The cheapest way to add warmth: about $75 to $250 and zero running cost.
- +Cuts evaporation, the biggest source of heat loss, by up to about 95 percent.
- +Slashes a heater's running cost by roughly 50 to 70 percent when you use both.
The verdict
A pool heater and a solar cover are not an either-or choice, because a heater adds heat and a cover keeps it. If you can only do one and you live somewhere warm and sunny, buy the solar cover: it is under a couple hundred dollars, adds about 5 to 10 degrees when used consistently, and costs nothing to run. If you want a set temperature you control, swim in spring, fall, or on cool nights, or need to heat fast, you need a heater, and gas heats fastest while a heat pump runs cheapest. For most heated pools the right answer is both, in that order: get the cover first because it also cuts any future heater's running cost by roughly 50 to 70 percent, then add a heater when the cover alone cannot reach your target. The one setup to avoid is a heater with no cover, which means paying full price to reheat the pool every night. Size a heater to the water with the pool volume calculator, compare the heater types in our how to heat a pool guide, and pick gear from the best pool heaters and best solar pool covers roundups.
Related: Solar vs heat pump pool heater, Gas vs heat pump pool heater, How to heat a pool.
Frequently asked questions
Are solar covers better than pool heaters?
Neither is better, because they do different jobs. A solar cover only slows heat loss and captures free sun, so it adds about 5 to 10 degrees in a warm, sunny climate and costs nothing to run, but it cannot hit a target temperature or heat in cool, cloudy weather. A heater actively adds heat, so it holds any temperature you set in any weather, but it costs $1,500 or more to install and something to run every month. For pure value in a warm climate, a solar cover wins because it is cheap and free to run. For dependable heat you control, a heater wins. Most heated pools want both: the cover makes the heater far cheaper to run.
Does a pool heat faster with a solar cover on or off?
On. A pool heats faster and holds its warmth better with the solar cover on, because the cover shuts down evaporation, which is the single biggest way a pool loses heat. An open pool does soak up slightly more direct sun during peak afternoon, but it loses far more to evaporative cooling the rest of the day and overnight, so on balance the covered pool comes out ahead. A clear or light blue cover still transmits plenty of sunlight to the water while blocking that evaporation, so leave it on while you are warming up. The only time to pull it is when the pool is already too warm and you want it to cool off.
Can I run my pool heater with my solar cover on?
Yes, and you should. Running the heater with the cover on is the most efficient way to heat and hold a temperature, because the heater adds the warmth and the cover keeps it from escaping, so the heater cycles on less and runs shorter. There is no harm to the heater from operating under a cover. The one thing to watch is that a cover traps heat well, so on a warm day the water can climb past your set point faster than you expect; just check the temperature now and then and pull the cover if it overshoots. Pairing the two typically cuts heating costs by roughly 50 to 70 percent.
How much warmer will a solar cover make a pool?
About 5 to 10 degrees Fahrenheit when you use it consistently, in a climate with real sun. Most of that gain is heat the pool would have lost to overnight evaporation that the cover instead kept in, which is why the cover has to stay on most of the time to work. Leave it off in the evenings and you give back the day's warmth. Used faithfully, a cover can move a pool from an uncomfortable mid-70s into the low 80s and add a few weeks to each end of the season. It does nothing on a cloudy day or a cold night, though, and it cannot hold a set temperature the way a heater does.
What is the most economical way to heat a swimming pool?
A solar cover is the cheapest single move, and pairing it with the right heater is the most economical setup overall. Start with a solar cover, because it adds a few degrees for well under $250 and then cuts the running cost of any heater by roughly 50 to 70 percent. For the actual heating, solar panels have the lowest running cost (free sun) where you have the roof space and climate, and a heat pump is the most efficient powered option because it moves heat from the air rather than burning fuel. Gas heats fastest but costs the most to run, so it is economical only when you heat occasionally and on demand. The cheapest real-world combination for most pools is a solar cover plus a heat pump, kept on a cover whenever no one is swimming.