Two pools, run end to end

Example A — a family pool in a humid climate

Inputs: a 30 by 15 ft rectangle, 4.5 ft average depth, held at 82 °F in Atlanta, GA, April through September, typical suburban wind exposure, no cover.

Evaporation is 64% of the loss here, which is typical for a humid Southeastern location — high, but not extreme, because the air itself carries a fair amount of moisture most of the season. A heat pump run at this pool's default cover-free, typically-exposed configuration costs $692 for the season, against $1,616 for natural gas at GA's published rate. This is a pool where the equipment choice, not the site conditions, is doing most of the work in the cost comparison.

Example B — a larger pool in a hot, dry climate

Inputs: a 36 by 18 ft rectangle, 5.0 ft average depth, held at 86 °F in Las Vegas, NV, March through October — a near year-round desert season — open wind exposure, no cover.

This is the case worth sitting with. The air in Las Vegas, NV is hot for most of this season, which sounds like it should mean easy, cheap heating. It does not: evaporation is 83% of the loss, 19 points higher than Example A, because dry desert air pulls moisture off the water surface aggressively regardless of air temperature. Combined with a longer season and an open, unsheltered site, the heat pump season cost reaches $6,539 — an order of magnitude above Example A, on a pool only about 44% larger in surface area.

Adding a bubble cover for 14 hours a day to this exact pool cuts net heat to supply to 261.97 million Btu and the heat-pump season cost to $2,271 — a reduction of 65%. In a climate this dry, a cover is not a marginal nicety; it is close to the single most consequential purchase available, cheaper than any heater upgrade and larger in effect than switching fuels.

What the two pools ask of the equipment

Cost is not the only thing that diverges. Example A's required heater output is 150,268 Btu/h; Example B's is 428,207 Btu/h — 2.8× larger, which is a bigger gap than the 1.4× difference in surface area alone would suggest, because Example B is also carrying a longer season and a higher setpoint into the same sizing calculation. A heat pump sized for Example A's load would not come close to covering Example B's; installing "the same heater, just bigger" is not a shortcut past the sizing page's two-question method, it is that method run on different inputs.

The season-average coefficient of performance tells a related story. Example A's heat pump runs at a season COP of 4.55; Example B's at 4.99 — higher, not lower, despite Example B costing far more to run overall, because Example B's season spends more of its time in warm air where a heat pump's coefficient of performance is close to its rated figure. The heat pump page derates any nameplate against real air temperature; these two examples show why a quoted COP means very different things in a mild-winter desert season and a humid six-month season that still dips into a cooler April.

What the contrast is actually showing

Neither example is a "typical" pool — they were chosen to be different from each other on purpose, the way the climate page's full comparison does at larger scale. The lesson is the one the price drivers page makes with a single pool: air temperature alone is a poor predictor of heating cost, humidity and wind exposure move the number more than most people expect, and the fix for a bad site — a cover, a windbreak, a shorter season — usually costs less than the equipment upgrade the bill seems to be asking for.

Run your own pool, your own climate and your own season on the main calculator. These two examples exist to show the method working end to end, not to stand in for your yard.