Every mini tank water heater gets a score from 0 to 100% built from five 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 tank size: 2.5 to 4 gallons, 6 to 10 gallons and 12 to 20 gallons.
| Factor | Measures | Weight |
|---|---|---|
| Value | price per gallon of tank, scaled by size group | 30% |
| Warranty | tank (leak) warranty 60%, parts warranty 40% | 30% |
| Heating power | element wattage, which sets how fast the tank reheats | 15% |
| Features | plug-in cord, relief valve and wall bracket included | 15% |
| Tank size | gallons, within its size group | 10% |
Where the numbers come from
Tank size, element wattage, electrical connection, included parts and warranty come from the maker’s specification sheet or manual where one is published, and otherwise from the maker’s own copy on a retail listing. Where the two disagree, the maker’s sheet is used and the product page notes it. Prices are checked at Amazon, and the lowest price at a store the page links to is used.
The factors
Value is the current price divided by the tank’s capacity in gallons, on a log scale, so halving the price always counts the same. Small tanks always cost more per gallon, so each size group has its own scale: from $90 a gallon (zero) to $40 (full marks) for 2.5 to 4 gallons, $50 to $20 for 6 to 10 gallons, and $30 to $12 for 12 to 20 gallons.
Warranty is 60% the tank (leak) warranty, scored from 1 year (zero) to 8 years (full marks), and 40% the parts warranty, scored from none to 6 years.
Heating power is the element’s wattage: 1,300 W scores zero and 2,000 W full marks. On the same 120 V circuit, more watts reheat the tank faster.
Features is 40% for a cord that plugs into a standard outlet, 35% for an included temperature and pressure relief valve, and 25% for an included wall bracket.
Tank size places the tank within its group: 2.5 to 4 gallons, 6 to 10 gallons and 12 to 20 gallons each run from zero at the smallest to full marks at the largest.
What isn’t scored
Recovery time, thermostat range, dimensions, weight, water connection size and release date are listed but not scored. Makers state recovery at different temperature rises, so the figures can’t be compared directly.
Missing data
Warranty is the factor that separates these heaters most, so a maker that doesn’t publish one gets no warranty counted: that factor scores zero and is marked estimated. A tank warranty published without a parts warranty counts the parts share as zero. Features work the same way: a feature the maker doesn’t mention counts as absent, and a heater whose listing names none of them scores zero for features, marked estimated. Any other figure that isn’t published gets the neutral middle score (50), marked estimated on the product page.
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.