Solar panels vs a gas pool heater
The widest gap in the whole category: zero running cost against the fastest heat you can buy. Almost nobody genuinely wants both halves.
Quick picks
Both technologies plus the cover that improves either one. If you buy gas, the cover cuts the hours you burn fuel; if you buy solar, it is what keeps the day's gain overnight.
| # | Product | Best for | Price |
|---|---|---|---|
| 1 | No photo The free option SmartPool SunHeater S601P Solar Heating System Panels plumbed into the return line. $0.00 per million BTU, forever, and no thermostat. | Adding real heat with no running cost, on a sunny site | |
| 2 |  The fast option Raypak Digital Natural Gas Pool Heater About six hours to lift a full-size pool ten degrees, whatever the weather is doing. | Heating fast and occasionally, rather than holding a temperature | |
| 3 |  The smaller gas option Hayward Universal H-Series 150,000 BTU Natural Gas Heater Half the gas demand, which is often what decides whether your existing line will feed it. | A modest pool where the gas supply, not the heater, is the real constraint | |
| 4 |  Buy this whichever way you go Sun2Solar 1600 Series Ultimate Blue Solar Cover Solar panels and gas heaters both put heat in. A cover is the only thing here that stops it leaving. | An inground pool you cover most nights, every season |
#ad We earn a commission if you buy through this link, at no extra cost to you. It never changes the ranking. How this site is funded. Prices last checked October 17, 2026.
The two numbers that frame it
This comparison has the widest spread of any pairing on the site, and it runs in opposite directions on the two axes that matter.
| Solar collector panels | Natural gas heater | |
|---|---|---|
| Cost per million BTU delivered | $0.00 | $28.36 |
| 20,000 gal, +10°F | $0.00 | $47.24 |
| Time for that job | Days of good sun | About 6 hours |
| Works in cold air | Poorly — it needs sun, not warmth | Yes, unaffected |
| Thermostat | No, in any meaningful sense | Yes |
| Install | Plumbing plus unshaded collector area | A gas line sized for the burner |
| Moving parts | None | Burner, blower, ignition, controls |
Gas figures use US average residential natural gas at $24.09 per thousand cubic feet (EIA, June 2026) and an assumed 82% thermal efficiency; the solar figure is zero because the filtration pump is already running. The derivation is here.
There is no clever reading of that table. Solar is free and slow, gas is fast and dear, and no amount of shopping changes either fact because both come from the physics rather than from the product.
The question that decides it
Are you extending a season, or rescuing a weekend?
Solar panels are a season-extension technology. They add heat gradually, across weeks, in proportion to how much sun your site gets. If your ambition is a usable pool through more of June and September — the shoulder weeks either side of the obvious summer — that is exactly what they are good at, and the running cost being genuinely zero means the extension is free every year after the install.
Gas is an on-demand technology. It exists to take a cold pool and make it swimmable this afternoon, and it will do that in about six hours regardless of cloud, air temperature or time of year. If you use the pool unpredictably — visitors at the weekend, a warm spell in April — that responsiveness is the entire product and it is worth paying for.
The failure mode in each direction is specific. Buy solar for responsiveness and you will spend a cold cloudy week watching panels deliver nothing. Buy gas to hold a temperature all season and you will get a fuel bill that makes you stop using it.
What solar actually requires
The zero running cost is real, and the install requirements are the reason not everyone has it:
- Unshaded collector area equal to roughly 50 to 100% of the pool’s surface, per the trade rule of thumb. That is a lot of roof or ground, and it has to be clear of shade through the middle of the day, which is usually the binding constraint rather than the area itself.
- Plumbing. The panels go inline after the filter. On a roof that is real work and it is where the install cost lives.
- Freeze protection. Panels full of water in a hard freeze split. In a freezing climate they have to drain down for winter, every year.
The solar roundup goes through this properly, and the home-built version is a genuine option here in a way it is not for any other heating technology.
What gas actually requires
The surprise on the gas side is almost never the heater. It is the supply. A heater has to be fed by a gas line sized for its input rating, and a line serving a house was not specified with a 336,000 BTU appliance in mind. Upsizing a gas run can cost more than the heater.
That is the practical argument for the smaller class of gas heater. A 150,000 BTU unit asks less than half as much of the supply, and takes about fourteen hours rather than six for the same job. On a modest pool the extra hours are often much cheaper than the new gas line.
And if you have no natural gas at all, “gas heater” means propane for you, at about $35.66 per million BTU delivered — roughly a quarter again on top of natural gas, which widens the gap against solar further.
The combination almost nobody considers
The purchase that comes before either
Both machines on this page put heat in. Neither addresses the roughly 70% of a pool’s heat loss that the Department of Energy attributes to evaporation, so both of them spend their day replacing heat that a cover would simply have kept.
On a gas heater that saving is money every time you fire it. On solar panels it matters even more, because their output is capped by the sun rather than by your budget — a cover is the only way to make a fixed daily gain go further. Cover picks here, and the cover-against-heater argument if you can only buy one thing this season.
So which one
Solar if you have the unshaded area, your goal is more weeks rather than more control, and you intend to keep the pool long enough to bank a decade of zero running cost.
Gas if you heat on demand, if your pool sits shaded or your roof faces the wrong way, or if you need a reliable temperature in the cold shoulder months when solar has nothing to give.
Neither, yet if your pool drops several degrees overnight. Fix that first and both of these get cheaper. The full ranked comparison across every heater type puts heat pumps into the picture as well, which for a lot of pools turns out to be the answer neither of these two is.
Every pick, in detail
What each one publishes, what is good and bad about it, and — the section this category usually omits — what we could not judge without owning one.
SmartPool SunHeater S601P Solar Heating System
Solar panels that plumb into the return line and heat the water with sunlight rather than fuel, which puts their running cost at zero — the only entry in the whole heating category where that is true. The trade is that you cannot dial in a temperature: the panels deliver what the sun gives them on the day, and on a cloudy week they deliver very little.
Best for Adding real heat with no running cost, on a sunny site
| Type | Roof, rack or ground-mounted solar collector panels, plumbed inline | Manufacturer |
|---|---|---|
| Collector area | Two 2 x 20 ft panels, 80 sq ft totalThis is the number to size from. The trade rule of thumb is collector area equal to 50-100% of the pool's surface, so a 16 x 32 pool needs several of these systems rather than one. | Manufacturer |
| Material | Polypropylene, stated not to corrode or scale | Manufacturer |
| Also required | One SK21 System Installation Kit per installation, sold separatelyThe manufacturer's own wording. One SK21 serves up to four of these two-panel systems. The panels on their own are not a complete installation, which is the commonest surprise in this product category. | Manufacturer |
| Running cost | $0 in fuelThe circulation pump is already running for filtration. There is no additional fuel or electricity cost attributable to the heat. | Our arithmetic |
Up to 6 to 10 degrees F
Claimed by SunHeater, on its own product page for the S601P. Conditions: Stated as under favorable conditions; no time period given. Source
Worth reading beside the figure below. The manufacturer's own claim for this product is 6 to 10 degrees. The retail listings for the same model say up to 15. The larger number is the one further from the manufacturer.
As much as 15 degrees F
Claimed by Bob Vila, describing the S601P. Conditions: Stated as requiring ample sunlight; no time period given. Source
Note the phrasing: with ample sunlight it can boost temperature by as much as 15 degrees. That is a cumulative ceiling reached over days of good sun, not a figure you will see in an afternoon.
- Zero fuel cost, forever — nothing else in this category can say that
- No combustion, no gas line, no additional electrical service
- Panels can be added to as the budget allows
- You get the sun's schedule, not yours
- Needs real unshaded mounting area, and plumbing work to install
- Does nothing on a cold cloudy week, which is when you most want it
- Actual heat output at your latitude, roof pitch and shading
- How the panel material survives a decade of UV and freeze cycles
- Whether the included fittings suit your existing plumbing
These need a unit in hand across a season. We do not have one, so we do not have an opinion worth printing on them.
#ad We earn a commission if you buy through this link, at no extra cost to you. It never changes the ranking. How this site is funded. Prices last checked October 17, 2026.
Raypak Digital Natural Gas Pool Heater
The right answer when speed matters more than running cost — a weekend pool you want warm on Friday afternoon rather than one you hold at temperature all season. At the assumptions we publish, gas costs roughly two and a half times what a heat pump costs per delivered BTU, and it will get there in a fifth of the time. Buy the speed if you need the speed.
Best for Heating fast and occasionally, rather than holding a temperature
| Type | Natural gas or propane fired, digital controlThe manufacturer publishes no retrievable specification sheet; figure is as listed at retail. | Retail listing |
|---|---|---|
| Rating convention | Rated by BTU/hr INPUTA 400,000 BTU gas heater burns 400,000 BTU an hour and delivers roughly 82% of it. Do not compare that number directly against a heat pump's output rating. | Published standard |
| Cost per million BTU delivered | About $28.36 at our published assumptionsUS average residential natural gas at $24.09/Mcf (EIA, June 2026) and an assumed 82% thermal efficiency. | Our arithmetic |
- Fast — hours rather than most of a day on a full-size pool
- Works the same in cold air, unlike a heat pump
- Lower purchase price than a heat pump of equivalent real output
- Roughly two and a half times a heat pump's cost per delivered BTU
- Needs a gas line sized for it, which is often the real cost
- Propane instead of natural gas raises the running cost by about a quarter again
- The efficiency this specific unit achieves in service
- Heat exchanger life against your water chemistry
- Whether your existing gas supply can feed it without an upgrade
These need a unit in hand across a season. We do not have one, so we do not have an opinion worth printing on them.
#ad We earn a commission if you buy through this link, at no extra cost to you. It never changes the ranking. How this site is funded. Prices last checked October 17, 2026.
Hayward Universal H-Series 150,000 BTU Natural Gas Heater
The gas heater for a pool that does not need 336,000 BTU an hour thrown at it. At 150,000 BTU/hr of input it is under half the fire of a full-size unit, which costs you speed and buys you something people discover too late: a much smaller gas supply to feed. On a modest inground pool or a big above-ground one, that is often the difference between using the gas line you already have and paying to upsize it.
Best for A modest pool where the gas supply, not the heater, is the real constraint
| Rated input | 150,000 BTU/hrHayward publishes this as a BTU/hr rating, in the gas convention: fuel burned per hour, not heat delivered into the water. | Manufacturer |
|---|---|---|
| Current part number | W3HS150FDN, which Hayward's listing states replaces the H150FDNSame heater class, current SKU, with the OmniX control. The older H150FDN part number still appears in older reviews and stock. | Retail listing |
| Heat exchanger | Standard cupro nickelCupro nickel is the corrosion-resistant option on most gas heaters and a paid upgrade on some. Hayward lists it as standard on this one. | Manufacturer |
| Thermal efficiency | Not stated for the current W3HS150FDNConfirmed on Hayward's own product page, read 17 October 2026: there is no thermal efficiency percentage anywhere on it. The only efficiency-shaped figure is a claim of savings of 'up to 18%', which refers to reduced PUMP run time rather than to combustion. An 84% figure circulated in retail copy for the older H150FDN; it does not appear for the current part, so we no longer attach it and run this heater at the 82% we assume for gas generally. | Manufacturer |
| Water flow window | Min 20, max 125Quoted exactly as Hayward publishes it — the specification table does not state the unit, though gallons per minute is the convention and the figures only make sense that way. Hayward advises keeping flow above the minimum with allowance for a dirty filter, to protect the exchanger. | Manufacturer |
| Connections | 2 in x 2-1/2 in CPVC unions | Manufacturer |
| Electrical | 120/240V, 60 Hz single phase, 5.5 circuit amps, 15 A max breakerHayward's table also carries a 'Power: 44 kW' row, which cannot describe this appliance: 5.5 A at 240 V is about 1.3 kW, and 44 kW would not sit behind a 15-amp breaker. We read it as a data-entry artifact and flag it rather than repeat it. | Manufacturer |
| Warranty | 1 year parts, no laborAt the shorter end of this category. For contrast, FibroPool states a Limited Lifetime warranty and TURBRO gives 2 years on the machine with 5 on the compressor, both on much cheaper units. | Manufacturer |
| Cost per million BTU delivered | About $28.36 at our 82% assumptionUS average residential natural gas at $24.09/Mcf (EIA, June 2026) divided by 82%, the same assumption we apply to every gas heater without a published efficiency figure. | Our arithmetic |
- Roughly half the gas demand of a full-size heater, which is often what decides the install
- Cupro nickel heat exchanger listed as standard rather than as an upgrade
- Low NOx certified, so it is permitted in the air districts that require it
- Slow for a gas heater: about 14 hours to lift 20,000 gallons ten degrees
- Still gas, so still roughly two and a half times a heat pump's cost per delivered BTU
- Hayward publishes no thermal efficiency figure for it on its own product page
- The thermal efficiency it actually delivers — no figure is published for the current part
- How the cupro nickel exchanger holds up against your water chemistry
- Whether your gas meter and line can feed it without an upgrade
These need a unit in hand across a season. We do not have one, so we do not have an opinion worth printing on them.
#ad We earn a commission if you buy through this link, at no extra cost to you. It never changes the ranking. How this site is funded. Prices last checked October 17, 2026.
Sun2Solar 1600 Series Ultimate Blue Solar Cover
The cover to buy if you intend to keep using it in five years. 16 mil is the thickest tier the category sells, and thickness on a solar cover buys durability rather than heat — Bob Vila measured every cover in its hands-on group at the same 4 to 5 degrees, from 12-mil clear to 16-mil blue. Pay the extra for the one that survives being dragged over the coping twice a day, not for a temperature difference that did not show up in the only published one-hour test in this category.
Best for An inground pool you cover most nights, every season
| Price shown for | 24 ft roundThis product is sold in several sizes on one listing. The live price and photograph on this page are the ones Amazon returns for this variant; other sizes are priced separately. | Retail listing |
|---|---|---|
| Thickness | 16 milThe manufacturer publishes no retrievable specification sheet; figure is as listed at retail. | Retail listing |
| Color | Blue | Retail listing |
| Stated lifespan | 5 to 10 years for the 16-mil tierSwim University's published figure for 16-mil covers generally, not a Sun2Solar warranty statement. | Retail listing |
| Bubble side | Bubbles face the waterCategory-wide instruction, not brand-specific. The bubbles are the insulating layer and they have to touch the water. | Published standard |
4 to 5 degrees F in one hour
Claimed by Bob Vila, measured across all covers in their group. Conditions: One hour under 2pm sun on 89 to 92 degree F days. Source
Their figure was the same for every cover they put on the water. Read our reconciliation of what a one-hour reading actually measures before you plan around this number.
- Thickest tier sold, which is where the durability difference actually is
- Blue absorbs more of the incoming energy at the surface than clear does
- Cuts oversize to your pool shape with household scissors
- Heavy and awkward at 16 mil — a large inground cover is genuinely a two-person job without a reel
- Costs meaningfully more than the 12-mil version for no measured heating advantage
- Whether the seams hold up over five seasons of daily handling
- How the bubble layer survives repeated dragging over rough coping
- Whether the stated lifespan tier holds for this specific product line
These need a unit in hand across a season. We do not have one, so we do not have an opinion worth printing on them.
#ad We earn a commission if you buy through this link, at no extra cost to you. It never changes the ranking. How this site is funded. Prices last checked October 17, 2026.
Questions people actually ask
Is a solar pool heater cheaper than gas?
How much faster is a gas heater than solar panels?
Can solar panels replace a pool heater entirely?
Should I get solar panels or a gas heater for a pool I use at weekends?
- Average retail price of electricity to US residential customers: 18.34 cents/kWh, June 2026U.S. Energy Information Administration · read 2026-09-02
- US residential natural gas price: $24.09 per thousand cubic feet, June 2026U.S. Energy Information Administration · read 2026-09-02
- US residential propane price: $2.674 per gallon, week ending 30 March 2026U.S. Energy Information Administration · read 2026-09-02
- Energy content conversion factors: 3,412 BTU per kWh, 1,036 BTU per cubic foot of natural gas, 91,452 BTU per gallon of propaneU.S. Energy Information Administration · read 2026-09-02
- U.S. Department of Energy pool-energy figures (evaporation share, BTU per pound evaporated, cover savings, recommended temperatures, wind effect)Recreonics, reproducing and attributing the U.S. Department of Energy · read 2026-09-02
- Pool heater roundup: the 8.33 BTU per gallon per °F figure, attributed on the page to Alicia Toedter of Leslie'sBob Vila · read 2026-09-02
Every URL above was fetched and returned content on the date shown. Where a figure is ours rather than somebody else’s, the arithmetic is on the page and on the methodology page. If you find an error in it, we would genuinely like to know.
Read next
Gas pool heaters worth buying
Raypak, Hayward and Pentair gas heaters ranked, with the natural gas and propane arithmetic, the rating trap, and why the gas line usually decides which one you can actually have.
How to heat a pool with solar panels
How much collector area you actually need, where it can go, how it plumbs in, the pump specification that rules people out, and the system kit that is not in the panel box.
Which pool heater to buy
Every type of pool heater ranked on what it costs to deliver a million BTU into the water, how many hours it needs to do it, and what the install actually involves.
Solar pool heaters
Solar collector panels: zero fuel cost forever, at the price of getting the sun's schedule instead of your own. Ranked, with the trade stated plainly.
Solar panels vs a heat pump
Free-to-run solar collectors against a controllable heat pump. What each one is genuinely good at, and the case for running both.
Heat pump vs gas pool heater
The two options priced per delivered BTU and timed on the same pool, with the one question that decides which trade suits you.
The cheapest way to heat a pool
Cheapest to buy is a cover. Cheapest to run is solar, then a heat pump. The arithmetic for both, and a spending order that works at any budget.