Every gas pool heater gets a score from 0 to 100% built from four factors, which maps onto the 5-point rating shown on the site (a 0% score would be 1.5 stars; a perfect score, 5). Each factor is scored against fixed reference points, not against the other products in the list, so adding a new model never moves another model’s rating. Heaters are grouped by size, under 250,000 BTU/h and 250,000 and up, and heating input has its own scale for each group.
| Factor | Measures | Weight |
|---|---|---|
| Value | price per 1,000 BTU/h of input | 35% |
| Heating input | gas input, BTU/h | 25% |
| Efficiency | thermal efficiency | 20% |
| Warranty | residential warranty | 20% |
Where the numbers come from
Gas input, thermal efficiency, heat exchanger, venting, warranty and the rest come from the maker’s product page, spec sheet or installation manual, or the maker’s own copy on its Amazon listing. Prices are checked at Amazon and the maker’s own store, and the lowest is used. Where a model comes in natural gas and propane versions, they share one listing.
The factors
Value is the current price divided by the gas input in thousands of BTU/h, on a log scale, so halving the price per 1,000 BTU/h always earns the same points. Small heaters cost more per BTU, so each size has its own scale: under 250,000 BTU/h, $24 per 1,000 BTU/h scores zero and $12 full marks; for 250,000 and up, $20 scores zero and $9 full marks.
Heating input is the maximum gas input: for heaters under 250,000 BTU/h, 100,000 scores zero and 200,000 full marks; for 250,000 and up, 250,000 scores zero and 400,000 full marks.
Efficiency is the certified thermal efficiency: 80% scores zero and 86% full marks. Most gas heaters are 82 to 84% efficient, so a couple of points separate them; condensing heaters, at about 95%, get full marks.
Warranty is the length of the residential warranty on the heater: 1 year scores zero and 3 years full marks. Several makers give a shorter warranty, or none, to heaters bought online or installed by the owner; where a term depends on how the heater is bought or installed, the product page says so. Longer heat exchanger warranties are listed but not scored.
What isn’t scored
Low NOx certification, heat exchanger material, ignition, venting, controls and weight are listed but not scored. Independent tests are listed where they exist, but there are too few to score.
Missing data
If a figure isn’t published, that factor gets the neutral middle score (50) and the product page marks it as estimated.
Ties and discontinued models
Products are ranked by score within each group. Discontinued models stay listed but rank below every current model and can be hidden with the “Hide discontinued” filter.