What is the difference between a solar and heat pump pool heater?
The difference is where the heat comes from and whether you get to control it. A solar pool heater is a set of dark collector panels, usually mounted on the roof or on a rack near the pool. Your pump pushes pool water up through the panels, the sun heats that water as it passes through, and the warmed water flows back to the pool. There is no fuel and no thermostat calling for heat; the panels warm the water whenever the sun is shining on them and do nothing when it is not. That is why solar is described as free heat, because after the install the only cost is the pump energy to move the water.
A heat pump works nothing like a furnace or an electric coil. It runs a refrigerant compressor, the same idea as an air conditioner in reverse, to extract heat from the outside air and concentrate it into your pool water. Because it moves existing heat rather than burning fuel to create it, a heat pump is remarkably efficient for an electric appliance, returning about 4 to 6 units of heat for every unit of electricity it draws. It has a thermostat, so you set a target temperature and it runs until the water gets there, then cycles to hold it.
That one distinction, free but weather-driven versus paid but controllable, drives every other tradeoff between the two. If you are still deciding on a heater type at all, our best pool heater guide covers gas, heat pump, and solar options, and the gas vs heat pump comparison covers the other big matchup. To see how many degrees of heating your pool actually needs, start with the pool heater calculator.
Which is cheaper, solar or a heat pump pool heater?
Solar is far cheaper to run, close to free, while a heat pump costs roughly $50 to $150 a month to run in warm weather and more when the air turns cold. Solar has no fuel bill at all; once the panels are up, the only added cost is the pump energy to circulate water through them, and if you already run the pump during the day that increase is small. A heat pump, by contrast, draws real electricity every hour it runs, though its COP of 4 to 6 keeps that bill far below what a plain electric resistance heater would cost.
Upfront, the two land in a similar range. A solar panel system runs about $2,500 to $6,000 installed for a typical residential pool, and a DIY kit can come in under that. A heat pump runs about $3,000 to $6,000 installed once you include the unit and the dedicated electrical circuit it needs. So the sticker price rarely decides it; the running cost does. Solar's near-zero operating cost means it often pays back its install in a few years and then heats for free for the rest of its life.
There is one honest catch on solar's cost. If your panels sit on a high roof, you may need a booster pump to lift water that far, or you may have to run the main pump longer to move enough water through the collectors, and both add a little to the electric bill. It is still dramatically cheaper to operate than any other heater. If the lowest lifetime cost is your goal, solar wins clearly, and our best solar pool heater guide covers panel systems and kits.
Which heats better on cloudy days and at night?
The heat pump, and it is not close. A heat pump heats day or night, cloudy or clear, and holds whatever temperature you set on its thermostat, as long as the outside air stays above roughly 50 degrees Fahrenheit. That means you can decide the pool will be 84 degrees for a weekend party and actually get there, or keep it swimmable through a stretch of gray weather. A solar heater simply cannot do this; it only adds heat while the sun is on the panels, so a run of cloudy days or a cool evening leaves the water cold no matter what.
Where solar shines, literally, is extending your existing swim season on sunny days. Sized right, with collector area equal to 50 to 100 percent of your pool's surface, a solar system can keep the water comfortable weeks earlier in spring and later into fall, capturing daytime sun and banking it in the pool. It just does that heating on the weather's schedule, not yours, and it gives back that heat overnight unless you also use a cover. Pairing solar with a solar pool cover is the single best way to hold onto the heat the panels collect.
Both heaters share the same cold-weather ceiling, from opposite directions. Solar makes no heat at night or under clouds, and a heat pump loses output as the air falls toward freezing because there is less warmth in the air for it to harvest, stalling out near 45 to 50 degrees. Neither is a true cold-season heater; for heating a pool in genuinely cold weather, a gas heater is the tool, which is why gas still exists despite costing the most to run.
Solar or heat pump: which pool heater should you buy?
Buy a heat pump if you want heat you control. It holds a set temperature, works at night and under clouds, needs no roof space or particular sun exposure, and fits essentially any pool that has a 240-volt circuit nearby. Its running cost is real but modest for electric heat thanks to that COP of 4 to 6, and it is the more predictable, more flexible heater for the way most people actually use a pool. For the majority of owners who just want the water warm and reliable, the heat pump is the better standalone choice.
Buy solar if your priority is the lowest possible running cost and you have the two things it needs: good sun and enough roof or ground space for the panels. Solar is the right call for owners in sunny climates who mainly want to stretch their season and are happy to swim on the days the sun cooperates, and who like the idea of heating for free for a decade or more after the install. Just go in knowing you are trading temperature control for that free heat.
The best answer for many warm-climate pools is not either or; it is both. Solar does the free daytime heating and a smaller heat pump backs it up for cloudy days, evenings, and holding a target temperature, which is how you get dependable heat at close to solar's running cost. Whichever way you go, size the heater to your pool with the pool heater calculator and the pool volume calculator, and see specific units in our best pool heater and best solar pool heater guides.
Solar wins on
- +Near-zero running cost; the sun's heat is free once the panels are installed.
- +Panels last about 10 to 20 years, often longer than a heat pump.
- +No fuel, no emissions, and almost no moving parts to service.
Heat Pump wins on
- +Heats on demand, day or night and on cloudy days, and holds a set temperature.
- +Works on any pool with a 240-volt circuit, regardless of roof space or sun.
- +Still cheap to run for electric heat, delivering 4 to 6 units of heat per unit of power.
The verdict
Buy the heat pump for most pools. It heats day or night and through cloudy weather, holds whatever temperature you set, needs no roof space, and its running cost stays low for electric heat because it moves about 4 to 6 units of heat per unit of power. Choose solar instead when your top priority is the lowest running cost and you have strong sun plus the roof or ground space for panels equal to 50 to 100 percent of your pool surface, because after the install its heat is essentially free for 10 to 20 years. Solar's tradeoff is control: it only heats when the sun is out and cannot hold a set temperature. If you can swing it, pairing solar with a smaller heat pump gives you dependable, on-demand heat at close to solar's running cost. Size whatever you pick with the pool heater calculator, and compare specific units in our best pool heater and best solar pool heater guides.
Related: Best pool heaters, Best solar pool heaters, Gas vs heat pump heater.
Frequently asked questions
Which is better, a heat pump or a solar pool heater?
For dependable heat you can control, a heat pump is better: it warms the pool day or night and under clouds, and holds a temperature you set, as long as the air is above about 50 degrees. A solar heater is better on running cost, because it heats for free once installed, but it only works when the sun is on the panels and cannot hold a set temperature. Pick the heat pump if you want reliability and control, solar if you want the lowest running cost and have good sun and roof space, or pair them for both. See our best pool heater guide for specific units.
What is the cheapest way to heat a swimming pool?
Over the long run, solar is the cheapest way to heat a pool, because after the install the sun's heat costs nothing beyond a little pump energy. A solar pool cover is the cheapest add-on of all: it cuts evaporation, the biggest source of heat loss, and can raise water temperature several degrees on its own. Among heaters you pay to run, a heat pump is the cheapest to operate thanks to its COP of 4 to 6, well below the cost of gas or an electric resistance heater. Our best solar pool cover guide covers the cheapest heat boost you can buy.
What is the most efficient type of pool heater?
Solar is the most efficient in the sense that it uses free, fuel-free sunlight, so nothing you pay for is wasted. Among powered heaters, a heat pump is the most efficient, returning about 4 to 6 units of heat for every unit of electricity because it moves heat from the air rather than generating it. A gas heater is the least efficient to run but the fastest and the only real choice for genuinely cold weather. Match the type to your climate and how much control you want, and size it with the pool heater calculator.
How many solar panels do you need to heat a pool?
As a rule of thumb, your solar collector area should equal 50 to 100 percent of the pool's surface area, and closer to 100 percent or more in cooler climates or for a longer swim season. So a 400-square-foot pool surface usually wants 200 to 400 square feet of panels. The exact number of panels depends on their size and your roof's sun exposure and angle; a south-facing, unshaded roof needs fewer than a partly shaded one. A good solar installer sizes the array to your pool and location, and our best solar pool heater guide covers panel systems and kits.
Does a pool heat faster with a solar cover on or off?
A solar cover helps most by holding heat in, not by adding it, so for a solar or heat pump system the cover mainly stops the heat you paid for from escaping overnight. Evaporation is the biggest way a pool loses heat, and a cover nearly eliminates it, so a covered pool warms up faster overall and stays warm far longer. The one exception is a clear solar cover on a sunny day with no heater running, where the cover both traps heat and lets sun through. In practice, keep the cover on whenever you are not swimming to get the most from either heater.