How To Heat An Above Ground Pool: Gas, Heat Pump Or Solar?

An unheated above ground pool in most of the country is comfortable for about ten or twelve weeks a year. Add heat and that becomes five or six months, plus the ability to swim on a cool evening in July instead of looking at the water and deciding against it.

That's the real pitch for a pool heater, and it's a good one. But heating is also the single most expensive ongoing decision you'll make about your pool, and the three technologies available are genuinely different — not just in price, but in what they're physically capable of.

Here's how to choose.

The three options in one paragraph each

Gas heaters burn natural gas or propane and transfer that heat to your water through a heat exchanger. They produce a lot of heat quickly and they work in any weather. They cost the most to run.

Heat pumps don't create heat — they move it, pulling warmth out of the outside air and transferring it into your water, the same way an air conditioner works in reverse. They're dramatically cheaper to run and dramatically slower, and they stop working when the air gets cold.

Solar circulates your pool water through collectors that the sun warms. Nearly free to operate, entirely dependent on weather, and it can't hit a target temperature on demand.

Speed: this is the real difference

If you take one thing from this article, make it this.

A gas heater will typically raise an above ground pool's temperature by 2 to 6°F per hour, and considerably faster on the smallest pools. A heat pump manages roughly 0.5 to 2°F per hour — two to three times slower on the same pool.

Both figures depend heavily on pool size, because you're heating a fixed number of gallons. A 266,000 BTU heater moves a 12' round pool about four times faster than it moves a 24' round, simply because there's a quarter as much water. Be wary of any article quoting a single "degrees per hour" figure without mentioning pool size — most of those numbers are borrowed from inground pools, which hold two to four times what an above ground pool does and therefore heat far more slowly.

That difference decides how you can use your pool.

Gas is a heat-on-demand tool. Decide Saturday morning that you want to swim Saturday afternoon, and gas can get you there. Our post on how long it takes to heat an above ground pool works through the actual math for common pool sizes.

A heat pump is a temperature-maintenance tool. It's excellent at holding a pool at 84°F all season and poor at rescuing you from a cold snap. If you plan to run it only on the weekends you swim, you'll be disappointed.

Solar is a season-extension tool. It'll add several degrees over the course of sunny days and give you nothing on a cloudy week.

Climate: this decides whether a heat pump is even an option

A heat pump extracts heat from the air, so it needs there to be heat in the air. Efficiency drops as the temperature falls, they become substantially less effective below about 50°F ambient, and most residential units hit a low-ambient cutoff and shut down somewhere around 40 to 45°F.

That's not a flaw — it's how the physics works. But it has a hard consequence: in a northern climate, a heat pump can't give you the early spring and late fall weeks that are exactly the weeks you bought a heater for.

Warm and long seasons — the South, the Southwest, the Gulf: a heat pump is usually the better economic answer. Plenty of days above 50°F, and the operating savings compound over a long season.

Cold and short seasons — the Midwest, the Northeast, the Mountain West: gas is usually the right answer, because it's the only one of the three that works in April and October. This is most of our customer base.

Mild in-between climates: either can work. Decide based on whether you want speed or low running cost.

Running cost: the reverse ranking

Here the order flips completely.

Gas heater efficiency is measured as thermal efficiency — the share of the fuel's energy that ends up in your water. The Raypak Digital units we carry run at 82% thermal efficiency, which is solid for a residential atmospheric gas heater. But 82% of an expensive fuel is still expensive.

Heat pumps are measured by COP, or coefficient of performance. A COP of 5 means the unit delivers five units of heat for every one unit of electricity it consumes — because it's moving existing heat rather than making new heat. That's not 500% efficiency in a physics-breaking sense; it's just a fundamentally different mechanism, and it's why heat pumps cost a fraction as much per hour to run.

One important caveat on COP numbers: manufacturers rate them under warm test conditions, typically around 80°F air and 80°F water. Your real-world COP on a 60°F morning will be considerably lower. Department of Energy analysis has put realistic regional values closer to the high 3s in colder conditions and above 5 in warmer ones.

Solar costs essentially nothing to run beyond the pump time you're already paying for.

We work through the actual arithmetic — therms, gallons of propane, kilowatt-hours — in what it costs to run a pool heater.

Up-front cost and installation

Gas has moderate equipment cost but the installation is the variable. You need an adequately sized gas supply line, correct venting and clearances, and an electrical connection. If your gas meter and line can't support the heater's demand, the upgrade can cost more than the heater. Read what a gas pool heater installation actually requires before you buy — that post exists specifically to stop people from ordering a heater they can't hook up.

Heat pumps typically cost more for the unit and need a dedicated 230V circuit at meaningful amperage, which usually means an electrician and possibly panel work. No gas, no venting.

Solar is the cheapest to buy and the most demanding of space. The rule of thumb is collector area equal to roughly half to all of your pool's surface area, which is a lot of roof or ground.

Lifespan and maintenance

Gas heaters generally give five to ten years in residential service — pool water and chemistry are hard on heat exchangers. Heat pumps often run ten to fifteen or more, partly because they have fewer components in contact with pool water.

If you run salt, this matters: a titanium heat exchanger is the correct specification for a heat pump in a salt pool and is standard on quality units. And if you're running salt on a steel wall pool, read our guide on that first — there's a warranty issue you need to know about.

Side by side

So which should you buy?

Buy gas if you're in a climate with a real winter, you want to swim on decision rather than on schedule, you want the shoulder seasons of April and October, or you have natural gas at the house already.

Buy a heat pump if you're in a warm climate with a long season, you'll run it continuously to hold a temperature, and you care most about the operating bill.

Buy solar if your budget is tight, you have the space and the sun, and you'd be happy with a few extra degrees rather than a set temperature.

Buy nothing yet if you don't have a solar cover. Genuinely — see the next section.

Before you buy any heater, buy a cover

The most common mistake we see is spending real money on a heater and then losing most of its output overnight.

The great majority of a pool's heat loss is evaporation off the surface. A solar cover stops that, and it costs a small fraction of any heater. Owners who add a cover often find the pool is warm enough that they need less heater than they thought, and owners who run a heater without one are paying to heat the sky.

We've written a full post on why the heater and cover combination works so well, and it's probably the highest-value thing in this whole cluster.

Getting the size right

An undersized heater never reaches your target on cool days. An oversized one costs more than it needed to. Our existing guide to what size pool heater you need covers the sizing math, and if you've settled on gas, which Raypak model to choose walks through BTU, fuel type, ignition and — importantly — the elevation configuration that catches a lot of buyers out.

The short version

• Gas heats fast — roughly 2–6°F per hour on an above ground pool — and works in any weather. It costs the most to run.
• Heat pumps run cheap and heat slowly, around 0.5–2°F per hour, and they stop working below roughly 40–45°F ambient.
• Solar is nearly free and entirely weather-dependent.
• Climate is usually the deciding factor: cold or short season means gas, warm and long season means a heat pump is worth considering.
• Gas is heat-on-demand. A heat pump maintains a temperature. They aren't interchangeable.
• Check your gas supply and your electrical panel before you buy anything.
• Add a solar cover regardless. It's the cheapest heat you'll ever buy.