A heated pool extends your swimming season by weeks or even months. But the wrong heating method can cost you a fortune in energy bills or leave you frustrated by how long it takes to warm the water. Each heating option has a clear set of strengths and trade-offs.
This guide compares the four main pool heating methods so you can pick the one that fits your climate, budget, and patience level.
The Four Pool Heating Methods
Gas Heaters
Gas pool heaters burn natural gas or propane to heat water as it passes through the unit. They are the fastest way to heat a pool and work regardless of outside air temperature.
How it works: Pool water flows through a heat exchanger. A gas burner heats the exchanger, and the water absorbs that heat before returning to the pool. The process is simple and effective.
Heating speed: A gas heater can raise pool temperature 1 to 2 degrees per hour depending on the heater size and pool volume. A 400,000 BTU heater can take a 20,000-gallon pool from 60 to 80 degrees in about 12 to 16 hours.
Upfront cost: $1,500 to $3,500 for the unit. Installation adds $500 to $1,500 depending on whether you need a gas line run to the equipment pad.
Operating cost: This is where gas heaters get expensive. Running a 400,000 BTU gas heater costs roughly $3 to $7 per hour depending on local gas prices. Heating a pool from scratch can cost $50 to $150. Maintaining temperature daily adds $5 to $30 per day. Monthly costs during swimming season run $200 to $600.
Best climate: Gas heaters work in any climate. They are the best choice for cold climates, occasional-use heating (weekend-only pools), and spas or hot tubs where you want fast heat on demand.
Lifespan: 5 to 10 years with proper maintenance. For detailed options, check our best pool heaters guide.
Electric Resistance Heaters
Electric resistance heaters work like a giant water heater. An electric element heats the water as it passes through.
How it works: Water flows over an electric heating element. The element converts electricity directly into heat. Straightforward engineering.
Heating speed: Slow. Electric resistance heaters are typically lower BTU than gas heaters and take significantly longer to raise water temperature. They can take 24 to 72 hours to heat a pool from cold.
Upfront cost: $2,000 to $5,000 installed. They require a dedicated electrical circuit, often 220V, which can add installation cost.
Operating cost: The most expensive method to operate. Electric resistance heating is nearly 100 percent efficient at converting electricity to heat, but electricity costs more per BTU than gas in most areas. Monthly costs can rival or exceed gas heating.
Best climate: Rarely the best choice for a full-size pool. They make more sense for small pools, spas, or as a supplement in mild climates. If your pool is small (under 10,000 gallons) and you are in a warm climate where you only need a few degrees of boost, they can work fine.
Lifespan: 10 to 15 years. Fewer moving parts means less to break.
Heat Pumps (Air-Source)
Heat pumps do not generate heat. They move it from the surrounding air into the pool water. This makes them dramatically more efficient than gas or electric resistance heaters.
How it works: The heat pump uses a fan to pull in outside air and pass it over an evaporator coil filled with refrigerant. The refrigerant absorbs heat from the air, a compressor concentrates that heat, and a heat exchanger transfers it to the pool water. It is the same principle as an air conditioner running in reverse.
Heating speed: Slow. Heat pumps raise pool temperature 1 to 3 degrees per day, not per hour. Getting a cold pool to swimming temperature can take 3 to 5 days. However, once the pool is up to temperature, the heat pump maintains it efficiently.
Upfront cost: $2,500 to $5,000 for the unit. Installation adds $500 to $1,000. They require a 220V electrical circuit.
Operating cost: This is where heat pumps shine. They produce 3 to 7 units of heat for every 1 unit of electricity consumed (measured as COP, or coefficient of performance). Monthly operating costs run $50 to $150 during swimming season, making them 3 to 5 times cheaper to run than gas or electric resistance heaters.
Best climate: Warm and temperate climates where air temperature regularly stays above 50 degrees. Heat pumps become less efficient as air temperature drops. Below 50 degrees, they struggle. Below 40 degrees, most units shut off. If you live where nights drop below 50 regularly during your swimming season, a heat pump will disappoint you.
Lifespan: 10 to 20 years. Longer than gas heaters with lower maintenance costs.
Solar Pool Heaters
Solar heaters use the sun to heat pool water directly. Water is pumped through solar collector panels (usually on your roof), where it absorbs heat before returning to the pool.
How it works: Your existing pool pump sends water through a series of solar collector panels. The panels absorb sunlight and transfer that heat to the water flowing through them. The heated water returns to the pool. A controller valve diverts water through the solar panels when they are warmer than the pool water, and bypasses them when they are not.
Heating speed: Variable. On a sunny day, solar panels can raise pool temperature 5 to 10 degrees over the course of the day. On cloudy or cool days, they may barely maintain temperature. They do not work at night.
Upfront cost: $3,000 to $7,000 installed for a full system. The panels themselves cost $1,000 to $3,000 depending on pool size and roof area. Installation and plumbing add $1,000 to $4,000.
Operating cost: Essentially zero. The pool pump pushes water through the panels, so the only added cost is a small increase in pump runtime, typically $10 to $30 per month in additional electricity.
Best climate: Sunny climates with lots of direct sunlight. Florida, Arizona, Southern California, and similar regions get the best return on solar heating. In cloudy or northern climates, solar alone usually is not enough to extend the season meaningfully. It works best as a supplement or in areas where you just need a few degrees of boost.
Lifespan: 15 to 25 years. Solar collectors have no moving parts and require minimal maintenance.
Comparison Table
| Feature | Gas | Electric | Heat Pump | Solar |
|---|---|---|---|---|
| Upfront Cost | $2,000 – $5,000 | $2,500 – $5,500 | $3,000 – $6,000 | $3,000 – $7,000 |
| Monthly Operating Cost | $200 – $600 | $200 – $700 | $50 – $150 | $10 – $30 |
| Heating Speed | Fast (hours) | Slow (days) | Slow (days) | Variable (sun dependent) |
| Works in Cold Weather | Yes | Yes | Below 50F, no | Limited |
| Energy Efficiency | 80-90% | 99% | 300-700% (COP) | Free energy |
| Lifespan | 5-10 years | 10-15 years | 10-20 years | 15-25 years |
| Maintenance | Moderate | Low | Low-Moderate | Very Low |
Solar Covers: The Secret Weapon
Regardless of which heater you choose, a solar cover (also called a solar blanket) is the cheapest and most effective supplement. A solar cover is a floating blanket that sits on the water surface when the pool is not in use.
Solar covers do two things. First, they reduce heat loss from evaporation by up to 95 percent. Evaporation is the number one way pools lose heat, accounting for 70 percent or more of total heat loss. Second, they passively absorb solar energy and transfer it to the pool, raising water temperature 5 to 15 degrees on their own.
A solar cover costs $50 to $200 and pays for itself in reduced heating costs within weeks. Every heated pool should have one. Check our best pool covers guide for options.
Which Heating Method Should You Choose
Pick Gas If:
- You want fast heat on demand (weekend use, parties, spas)
- You live in a cold climate where the air is often below 50 degrees during your swimming season
- You only heat the pool occasionally rather than maintaining temperature continuously
- You already have a natural gas line at the equipment pad
Pick Heat Pump If:
- You live in a warm or temperate climate (air temperature above 50 degrees during swimming season)
- You want to maintain a consistent pool temperature all season long
- You want low operating costs and are willing to plan ahead since it heats slowly
- You swim regularly and want the pool ready at all times
Pick Solar If:
- You live in a sunny climate with lots of direct sunlight
- You have adequate south-facing roof space for panels
- You want the lowest possible operating costs
- You are looking for an eco-friendly option
- You only need a modest temperature boost (5 to 15 degrees)
Skip Electric Resistance Unless:
- Your pool is very small (under 10,000 gallons)
- You cannot install gas or a heat pump at your location
- You need a supplemental heater for a spa that is rarely used
For overall pool costs and how heating fits into the ownership picture, see our guide on how much a pool costs. And if you are getting ready for pool season, our pool season prep checklist includes heater startup tasks.
Combining Heating Methods
Many pool owners use a combination. The most common pairings:
Heat pump plus gas heater. The heat pump maintains baseline temperature cheaply, and the gas heater provides a quick boost when you want the pool warmer for a party or weekend.
Solar plus heat pump. Solar panels provide free daytime heating, and the heat pump fills in during cloudy days and maintains temperature at night.
Solar plus solar cover. In warm, sunny climates, this combination can be enough on its own. The panels heat during the day and the cover retains that heat overnight.
A saltwater pool system pairs well with any heating method and does not affect your heater choice, though you should make sure your heater is rated for saltwater use to prevent corrosion.
Frequently Asked Questions
What is the cheapest way to heat a pool?
A solar cover is the cheapest single investment, costing $50 to $200 with zero operating cost. For active heating, solar panels have the lowest operating cost (near zero), followed by heat pumps ($50 to $150 per month). If you need to heat quickly and do not mind the operating cost, a gas heater combined with a solar cover gives you the best of both worlds.
How much does it cost to heat a pool per month?
Gas heaters cost $200 to $600 per month depending on temperature set point and pool size. Heat pumps cost $50 to $150 per month. Solar is $10 to $30 per month (just the added pump runtime). Electric resistance costs $200 to $700 per month. These are estimates for a typical 15,000 to 20,000 gallon pool maintaining 80 to 82 degrees.
Can a heat pump heat a pool in cold weather?
Most air-source heat pumps lose efficiency rapidly below 50 degrees Fahrenheit and most units have an automatic shutoff between 40 and 50 degrees. In cold climates, a heat pump alone will not be sufficient for extending the season into cold weather. You would need a gas heater for that purpose, either as the primary heater or as a supplement to the heat pump.
How long does it take to heat a pool?
Gas heater: 12 to 24 hours from cold to 80 degrees. Heat pump: 3 to 5 days from cold. Solar: highly variable, depends on sun exposure, but typically several days. Electric resistance: 24 to 72 hours. These times are for a typical 15,000 to 20,000 gallon pool. Larger pools take proportionally longer.
Is a solar cover worth it?
Absolutely. A solar cover reduces heat loss from evaporation by up to 95 percent and can raise pool temperature 5 to 15 degrees on its own. At $50 to $200, it is the single best investment for reducing heating costs regardless of what type of heater you use. The only downside is the hassle of putting it on and taking it off, which a solar cover reel ($100 to $300) solves.