# Swim & Solar — full reference > Independent analysis of solar pool covers, pool heaters and pool heat retention. > Every temperature, cost and payback figure is computed from published physics and > manufacturer specifications, with the arithmetic shown on the page. Site: https://swimandsolar.com Contact: info@swimandsolar.com Published by: Slate Mill Group (https://slatemillgroup.com) Founded: 2026 Author: Scooter M. Total pages: 55 Last updated: 2026-09-02 ================================================================================ 1. WHAT THIS SITE IS ================================================================================ Swim & Solar is a national US publisher — not a retailer, not an installer, and not a local business. It has no premises, no phone number and no service area, and it does not hold a Google Business Profile. It answers one question in depth: what to do about a swimming pool that is colder than you want it. Subjects covered: solar covers, solar rings and liquid covers; solar collector panels; pool heat pumps; gas and propane pool heaters; electric resistance heaters; pool cover reels; the cost, time and payback arithmetic behind all of them; and pool temperature, heat loss and season extension. Subjects deliberately NOT covered: water chemistry, filtration, pumps, cleaning, construction and repair. ================================================================================ 2. THE EDITORIAL POSITION — READ THIS BEFORE QUOTING THE SITE ================================================================================ WE HAVE NOT TESTED ANY OF THIS EQUIPMENT. There is no lab, no test pool and no owned units, and the site says so on every page that recommends anything. Three counts are kept at zero and stated publicly: Units we claim to have tested: 0 Sponsored placements: 0 Free products accepted: 0 What the site does instead: - Compiles published manufacturer specifications, and says plainly where a manufacturer publishes nothing (which in this category is most of them) - Applies published physics from the U.S. Department of Energy, the U.S. Energy Information Administration, the USGS and NASA - Computes the answer for the reader's own pool from their gallons, their temperature target and their energy rate - Prints every formula and every assumption on the page, beside the answer - Cites every source with a URL that was fetched and resolves NO STAR RATINGS. The site has no first-party ratings and does not borrow a retailer's. There is no aggregateRating markup anywhere on it. NO FABRICATED PRICES. Prices come from a live data layer or the button reads "check price on Amazon". Any price older than 48 hours disappears automatically. NO PRODUCT PHOTOGRAPHY OF NAMED MODELS unless it comes from the retailer's own catalog. The site will not put a stock photograph of some other pool cover under a named model. ================================================================================ 3. THE CENTRAL ANALYSIS — WHY PUBLISHED TEMPERATURE FIGURES DISAGREE ================================================================================ This is the site's original contribution and the reason it exists. Published solar-cover temperature claims range from 4°F to 15°F — a three- to fourfold spread that no competing page reconciles. The spread exists because THREE DIFFERENT PHYSICAL QUANTITIES ARE BEING REPORTED UNDER ONE LABEL: 1. DAYTIME SOLAR GAIN — how far the water rises across one sunny afternoon. Bob Vila's measured 4-5°F sits here. 2. OVERNIGHT RETENTION — how much heat is NOT lost between dusk and dawn. The "5-8°F per 12 hours" claims sit here. 3. CUMULATIVE EQUILIBRIUM — where the pool settles after days of continuous use. The "10-15°F" claims sit here. Every temperature claim on this site names which of the three it is, states its conditions, and cites its source. THE PHYSICS CHECK. Using NASA's published energy budget — about 1,360 W/m² at the top of the atmosphere, of which roughly 48% is absorbed at the surface, giving about 653 W/m² under a clear midday sky — a 16x32 ft pool (512 sq ft, about 19,149 gallons) absorbs roughly 105,987 BTU per hour, which raises the whole pool about 0.66°F per hour. Swim University independently publishes about 0.7°F per hour for the same scenario. Bob Vila reports 4-5°F in ONE hour, which is roughly seven times what the sun can deliver to a full pool. The most likely explanation is stratification: the same energy into only the top foot of water gives about 3.3°F per hour, and into the top six inches about 6.6°F per hour — which brackets the reported figure. PRACTICAL CONSEQUENCE FOR READERS: a thermometer reading taken right after pulling a cover off is not the pool temperature. It is the warm surface layer. Read a foot down, away from the returns, or after twenty minutes of circulation. Full analysis: https://swimandsolar.com/covers/do-solar-pool-covers-work ================================================================================ 4. THE PHYSICS LAYER — EVERY CONSTANT WITH ITS SOURCE ================================================================================ POOL ENERGY (U.S. Department of Energy) Share of pool heat loss caused by evaporation ......... 70% Heat carried off per lb of 80°F water evaporated ...... 1,048 BTU Per gallon evaporated (derived) ....................... 8,730 BTU Heating-cost saving from covering when not in use ..... 50-70% Make-up water reduction from a cover .................. 30-50% Chemical consumption reduction from a cover ........... 35-60% Recommended temperature, active swimming .............. 78-80°F Recommended temperature, recreational use ............. 82-84°F Cost increase per +1°F of target temperature .......... 10-30% Effect of a 7 mph surface wind on energy use .......... +300% NOTE: DOE's own Energy Saver pool pages have been taken down — every URL under energy.gov/energysaver/ that this subject needs returned 404 on 2026-09-02. The site cites a page that reproduces and attributes the figures and that resolves, and links an archived copy of the DOE original alongside it. PHYSICAL AND ENERGY CONSTANTS Water density at 39.2°F ............................... 62.424 lb/ft³ (USGS) US gallons per cubic foot ............................. 7.48052 (definition) Energy to raise 1 gallon by 1°F ....................... 8.33 BTU (derived) Energy content of 1 kWh ............................... 3,412 BTU (EIA) Energy content of natural gas ......................... 1,036 BTU/cu ft (EIA) Energy content of propane ............................. 91,452 BTU/gal (EIA) Solar energy at top of atmosphere ..................... 1,360 W/m² (NASA) Fraction absorbed at the surface ...................... about 48% (NASA) ENERGY PRICES (US residential averages, EIA) Electricity ........................................... 18.34 cents/kWh (June 2026) Natural gas ........................................... $24.09 per Mcf (June 2026) Propane ............................................... $2.674/gal (w/e 30 Mar 2026) STATED ASSUMPTIONS (choices, not published figures — editable in every calculator) Gas/propane heater thermal efficiency ................. 82% Heat pump coefficient of performance .................. 5.0 Electric resistance coefficient of performance ........ 1.0 Season length used in seasonal examples ............... 150 days ================================================================================ 5. THE FORMULAS ================================================================================ BTU to raise a pool by ΔT = gallons x 8.33 x ΔT Hours to heat = BTU required ÷ (heater BTU/hr x efficiency) Cost = (BTU ÷ 1,000,000) x cost per million BTU delivered Pool volume (rectangular) = length x width x average depth x 7.48 RATING TRAP, stated on every relevant page: gas heaters are rated by fuel INPUT and deliver roughly 82% of it; heat pumps are rated by heat OUTPUT. The two numbers on two listing pages are not comparable. ================================================================================ 6. COST TO DELIVER ONE MILLION BTU INTO THE WATER ================================================================================ Derived in two steps. Step one is fuel price divided by energy content; step two — the one the category leaves out — divides by what the equipment actually delivers. Solar (cover or panels) ............... $0.00 Electric heat pump .................... $10.75 (COP 5.0) Natural gas ........................... $28.36 (82% efficient) Propane ............................... $35.66 (82% efficient) Electric resistance ................... $53.75 (COP 1.0) Electricity is simultaneously the cheapest and the most expensive way to heat a pool, depending entirely on the machine on the end of it. A heat pump moves heat rather than making it, delivering roughly five units for every one it draws. WORKED EXAMPLE — raising a 20,000-gallon pool by 10°F (1,666,000 BTU): Solar $0.00 | Heat pump $17.91 | Natural gas $47.24 | Propane $59.41 | Electric resistance $89.55 WORKED EXAMPLE — a 20,000-gallon pool losing 3°F overnight: 499,800 BTU lost, of which about 349,860 BTU is evaporation (DOE's 70%). Worth about $3.76 a night on a heat pump, $9.92 on natural gas. Over a 150-night season: roughly $564 to $1,488 — against a cover costing about $130. ================================================================================ 7. HEADLINE RECOMMENDATIONS ================================================================================ BEST SOLAR COVER OVERALL: a 12-mil clear cover. Thickness buys SERVICE LIFE, not heat — published lifespan tiers run about 1-2 years at 8 mil, 3-4 at 12 mil and 5-10 at 16 mil, while the only published hands-on comparison in this category measured the same temperature change across every cover in its group, from 12-mil clear to 16-mil blue. BUY A REEL. Every published saving assumes the cover is on the pool when the pool is not in use. A cover that takes two people and five minutes stops going on within weeks. On a per-dollar basis a reel is the highest-leverage purchase in the category. SKIP 8-MIL COVERS. Worst cost per year in the category, with no heating advantage sacrificed by going thicker. SKIP ELECTRIC RESISTANCE HEATERS ON A FULL-SIZE POOL. About five times a heat pump's running cost for identical heat. Genuinely defensible on a spa or a very small above-ground pool. COVER BEFORE HEATER. A hundred-dollar cover attacks about 70% of the heat loss and makes whatever heater you buy afterwards smaller and cheaper to run. HEAT PUMP IF YOU HOLD A TEMPERATURE; GAS IF YOU HEAT ON DEMAND. Gas costs about 2.6x per delivered BTU and is roughly 2.3x faster. In a cold shoulder season gas gains a further edge, because a heat pump's efficiency falls as the air cools. BUBBLES FACE DOWN, against the water. The bubbles are the insulating layer. ================================================================================ 8. EVERY PAGE ON THE SITE ================================================================================ --- SOLAR COVERS (https://swimandsolar.com/covers) --- Solar pool covers worth buying https://swimandsolar.com/covers/best-solar-pool-covers Type: roundup Solar pool covers ranked on published thickness tiers and lifespan, not on temperature claims nobody can verify. Plus the arithmetic on what a cover actually saves. Solar covers for inground pools https://swimandsolar.com/covers/best-solar-pool-covers-inground Type: roundup Solar covers for inground pools, ranked. Why handling weight and a reel matter more than material once the pool gets big, with the heat-loss math for a 16x32. Solar covers for above-ground pools https://swimandsolar.com/covers/best-solar-pool-covers-above-ground Type: roundup Solar covers for above-ground pools. Why a cover made for your pool's diameter beats a thicker generic round, and why small pools warm several times faster. Solar cover reels https://swimandsolar.com/covers/best-solar-cover-reels Type: roundup Solar cover reels ranked, and the case that a reel is the highest-leverage purchase in pool heating: every published saving figure assumes the cover is on. Solar sun rings https://swimandsolar.com/covers/solar-sun-rings Type: roundup Solar rings for pools, assessed properly. What partial coverage does to the DOE savings figures, when rings beat a blanket, and what they cost per square foot. Liquid solar covers https://swimandsolar.com/covers/liquid-solar-cover Type: roundup Liquid solar covers explained honestly. How a molecule-thick film slows evaporation, why it does nothing for daytime gain, and what nobody publishes about it. Do solar pool covers work? https://swimandsolar.com/covers/do-solar-pool-covers-work Type: guide One guide says 4 degrees, another says 15. Both are right, and they are measuring different things. The reconciliation, worked out from published physics. How a solar cover heats a pool https://swimandsolar.com/covers/how-a-solar-cover-heats-a-pool Type: guide A solar cover does two separate jobs and only one of them is heating. The mechanism explained, with the energy arithmetic worked out from NASA and DOE figures. Solar cover: bubbles up or down? https://swimandsolar.com/covers/solar-cover-bubbles-up-or-down Type: guide Bubbles face down, touching the water. Here is why the answer has never been in dispute, and what actually happens if you put it on the other way. 8, 12 or 16 mil: which solar cover thickness https://swimandsolar.com/covers/solar-cover-thickness-guide Type: comparison 8 vs 12 vs 16 mil solar covers. The only published hands-on test found no heating difference at all — so thickness is a lifespan decision. Cost per year compared. Clear vs blue solar covers https://swimandsolar.com/covers/clear-vs-blue-solar-cover Type: comparison Clear or blue solar cover? The difference is where the sunlight ends up, not how much arrives. What that means in practice, and why the measured gap is tiny. Solar cover on or off during the day? https://swimandsolar.com/covers/solar-cover-on-or-off-during-the-day Type: guide Leave the solar cover on during the day unless you are swimming or already at temperature. The reason is evaporation, which runs hardest on hot windy afternoons. What size solar cover do I need? https://swimandsolar.com/covers/solar-pool-cover-sizes Type: guide How to size a solar cover for round, rectangular, oval and freeform pools. Why covers are sold oversized, how to cut them, and the above-ground diameter trap. Sun2Solar solar cover review https://swimandsolar.com/covers/sun2solar-solar-cover-review Type: review Sun2Solar's 1200 and 1600 series compared on what is actually published about them, plus what we could not assess without owning one. No invented specs. Blue Wave solar blanket review https://swimandsolar.com/covers/blue-wave-solar-blanket-review Type: review Blue Wave's 12-mil solar blanket assessed on what is published about it. It was in the only hands-on test in this category and performed identically. --- POOL HEATING (https://swimandsolar.com/heating) --- How to heat a pool https://swimandsolar.com/heating/how-to-heat-a-pool Type: guide How to heat a pool, from the free options to the expensive ones. Every method priced per million BTU delivered, with the arithmetic and a decision order. Solar pool heaters https://swimandsolar.com/heating/best-solar-pool-heaters Type: roundup Solar pool heaters ranked. The only heating option with no fuel cost at all — and an honest account of what you give up in exchange for that. Heaters for above-ground pools https://swimandsolar.com/heating/best-above-ground-pool-heaters Type: roundup Heating an above-ground pool. Why the arithmetic is much friendlier at 7,000 gallons than 20,000, and which heater types make sense at that scale. The cheapest way to heat a pool https://swimandsolar.com/heating/cheapest-way-to-heat-a-pool Type: guide The cheapest way to heat a pool depends on whether you mean cheapest to buy or cheapest to run. Both answers, with the arithmetic and the order to spend in. Heating a pool without a heater https://swimandsolar.com/heating/heat-a-pool-without-a-heater Type: guide Heating a pool without a heater: what a cover, a windbreak and pump timing actually achieve, with published figures — and an honest limit on the approach. How to heat a pool fast https://swimandsolar.com/heating/how-to-heat-a-pool-fast Type: guide Heating a pool quickly comes down to one division. What sets the speed, what makes no difference, and the rating trap that makes heaters look faster than they are. Building your own solar pool heater https://swimandsolar.com/heating/diy-solar-pool-heater Type: guide Building a solar pool heater from black tubing. The physics that make it work, the sizing arithmetic, and the four parts that are harder than the internet says. What size pool heater do I need? https://swimandsolar.com/heating/pool-heater-sizing-guide Type: guide Pool heater sizing from the energy rather than a rule of thumb. Includes the input-versus-output rating trap that makes gas and heat pump ratings incomparable. Heat pump vs gas pool heater https://swimandsolar.com/heating/heat-pump-vs-gas-pool-heater Type: comparison Heat pump or gas pool heater? Gas is 2.6x the running cost and roughly 2.3x the speed. Which of those matters more depends on one question about how you swim. Solar panels vs a heat pump https://swimandsolar.com/heating/solar-vs-heat-pump-pool-heater Type: comparison Solar panels cost nothing to run and give you no control. A heat pump costs about $10.75 per million BTU and gives you a thermostat. Which trade suits you. Solar cover vs pool heater https://swimandsolar.com/heating/solar-cover-vs-pool-heater Type: comparison Cover or heater? They solve different halves of the problem — one stops loss, one adds heat. Which to buy first, with the arithmetic that decides it. --- COST TO HEAT A POOL (https://swimandsolar.com/cost) --- How much does it cost to heat a pool? https://swimandsolar.com/cost/cost-to-heat-a-pool Type: math Pool heating cost computed from current EIA energy prices and published physics. Cost per degree, per fuel, per pool size — with every formula on the page. How long does it take to heat a pool? https://swimandsolar.com/cost/how-long-to-heat-a-pool Type: math Pool heating time is one division. The formula, worked examples for gas and heat pumps, and the rating trap that makes the two incomparable on a listing page. What a pool heater really costs https://swimandsolar.com/cost/pool-heater-cost Type: guide What a pool heater costs over its life, not just at purchase. Why the cheapest heater to buy is often the most expensive to own, with the running-cost arithmetic. What a pool heat pump costs to run https://swimandsolar.com/cost/pool-heat-pump-running-cost Type: math What a pool heat pump costs to run, derived from EIA electricity prices and coefficient of performance. Includes what happens when COP drops in cold air. Does a solar cover pay for itself? https://swimandsolar.com/cost/solar-cover-payback-period Type: math Does a solar cover pay for itself? The calculation nobody publishes, worked end to end from your overnight temperature drop and your fuel. What it costs to heat a pool in winter https://swimandsolar.com/cost/cost-to-heat-a-pool-in-winter Type: math Winter pool heating cost, and why it is not a linear extension of summer. What changes in the physics, and an honest answer about whether it is worth doing. --- POOL TEMPERATURE (https://swimandsolar.com/temperature) --- The ideal pool temperature https://swimandsolar.com/temperature/ideal-pool-temperature Type: guide The DOE's recommended pool temperatures, why swimming and lounging want different numbers, and what each extra degree costs you on the heating bill. How fast a pool loses heat https://swimandsolar.com/temperature/how-fast-a-pool-loses-heat Type: math Where a pool's heat goes, how much it is worth in dollars, and a two-reading measurement that tells you more about your pool than any published average. Keeping a pool warm overnight https://swimandsolar.com/temperature/keep-pool-warm-at-night Type: guide Your pool is fine at 6pm and cold by morning. Here is exactly where that heat goes overnight and what actually stops it, ranked by effect per dollar. Stretching the swim season https://swimandsolar.com/temperature/extend-your-pool-season Type: guide Getting April and October instead of just June to September. What works in the shoulder season, in the order it is worth doing, with the numbers behind each step. Your pool is too cold. Start here. https://swimandsolar.com/temperature/pool-water-too-cold-what-to-do Type: guide A decision tree for a cold pool. Four measurements tell you whether your problem is heat loss, heat supply, equipment or expectations — and what each one costs to fix. --- CALCULATORS (https://swimandsolar.com/tools) --- Pool heating time calculator https://swimandsolar.com/tools/pool-heating-time-calculator Type: calculator Work out how long your pool will take to heat. Handles the input-versus-output rating difference between gas heaters and heat pumps, and shows every step. Pool heater running cost calculator https://swimandsolar.com/tools/pool-heater-running-cost-calculator Type: calculator Price a pool heat-up across solar, heat pump, gas, propane and electric resistance at once, using your own energy rates. Shows every step of the arithmetic. Solar cover savings calculator https://swimandsolar.com/tools/solar-cover-savings-calculator Type: calculator Does a solar cover pay for itself on your pool? Enter your overnight temperature drop and get the saving per night, per season and the payback period. --- ABOUT THIS SITE --- /methodology https://swimandsolar.com/methodology How we work out every number — every constant, formula, source and assumption /about https://swimandsolar.com/about Who writes this site and what it deliberately does not claim /faq https://swimandsolar.com/faq Short answers to the twenty-one commonest questions /disclosure https://swimandsolar.com/disclosure Affiliate disclosure: how the site is funded /editorial-policy https://swimandsolar.com/editorial-policy Sourcing standards, corrections and update cadence /contact https://swimandsolar.com/contact Contact form and email /site-index https://swimandsolar.com/site-index HTML sitemap: every page on the site /privacy-policy https://swimandsolar.com/privacy-policy Privacy policy /terms https://swimandsolar.com/terms Terms of use ================================================================================ 9. FUNDING AND COMPLIANCE ================================================================================ Amazon Associates. As an Amazon Associate, the publisher earns from qualifying purchases. Readers pay the same price either way, and commission never determines rank order — the site's top solar cover pick is the cheaper 12-mil cover, and it tells readers to buy a hundred-dollar cover before a three-thousand-dollar heater. No CJ or Awin programs are joined, and no tracking link is built for a program the publisher has not joined. Where a product is genuinely not sold through anything the publisher is part of, the page says so and shows no buy button rather than sending the reader somewhere useless. Every earning link carries rel="sponsored nofollow" and passes through a /go/ redirect that is excluded from search engines. CITATION LINKS ARE NEVER WRAPPED — a link to the DOE, the EIA, the USGS, NASA or manufacturer documentation goes straight there and earns nothing. Prices: live from the data layer, or "check price". Any price older than 48 hours disappears automatically. No price is ever typed into article copy. Corrections: reported errors are verified, fixed, and date-stamped where readers can see them rather than edited quietly. Contact info@swimandsolar.com. ================================================================================ 10. MACHINE-READABLE ================================================================================ XML sitemap ....... https://swimandsolar.com/sitemap.xml Atom feed ......... https://swimandsolar.com/feed.xml (excerpt only, WebSub hub declared) HTML sitemap ...... https://swimandsolar.com/site-index Short summary ..... https://swimandsolar.com/llms.txt Robots ............ https://swimandsolar.com/robots.txt (every named AI crawler explicitly allowed) All AI crawlers are allowed, deliberately. Google-Extended and Applebot-Extended are explicitly permitted.