How we rank products

Every ranking on this site is calculated, not hand-picked. Here is the whole method.

1. Specs come from the manufacturer

We enter only figures published on an official ENERGY STAR certified-product record and we link the record we used under every product. If a figure isn't published we show "Not listed" instead of guessing.

2. Each spec is scaled from 0 to 1

Each criterion has a fixed reference range, from a "weakest reasonable" value to a "best in class" value (for example 3.20 to 4.50 uniform energy factor for 240-volt heat pump water heaters). A product's figure is placed on that range and clamped between 0 and 1, so scores stay meaningful as products are added. Yes/no features count as 1 or 0. The ranges are listed below.

3. Weights decide what matters most

Each category lists its criteria and weights on the page. The score is the weighted average, multiplied by 10:

score = 10 × Σ(weight × scaled value) ÷ Σ(weight)

4. How missing data is scored

If a spec isn't published, the product scores at the lowest value any product in that category actually published, so an unpublished figure never outranks a published one. The page marks each such cell with an asterisk. Yes/no features that aren't stated count as no. Nothing is ever scored at the category average. Connected-capable is scored as Yes only when the official ENERGY STAR record marks that field as Yes. Unstated counts as no.

5. Prices and ratings switch on automatically

When our retailer feeds supply a current price or customer rating for at least 60% of products in a category, two more criteria join the formula: Price / value (20%) and Customer rating (15%, discounted when there are few reviews). Until then we show "Check price" and never estimate a price.

6. What the score can't tell you

Specs don't capture installation cost, how loud a heat pump compressor is in your utility room, or whether your gas line can feed a tankless unit. Uniform energy factor and first-hour rating are the official ENERGY STAR figures, which can differ from older energy-factor or brochure first-hour claims. When we divide certified annual energy use by certified storage volume, or maximum GPM by gas input, we label those figures computed. Use the score to shortlist, then read the pros, cons, safety notes and sources. When we add hands-on testing notes, we label them clearly.

7. Money never changes the order

We earn affiliate commissions from some retailers. Commission rates are not an input to the formula, and no brand can pay for placement. See our affiliate disclosure.

Criteria by category

240-Volt Heat Pump Water Heaters

• Uniform energy factor: 36% · range 3.2 → 4.5
• First-hour rating: 28% · range 55 → 101 gallons
• Certified storage volume: 18% · range 36 → 82 gallons
• Connected capable: 18% · yes/no

120-Volt Heat Pump Water Heaters

• Uniform energy factor: 40% · range 2.8 → 3.5
• First-hour rating: 36% · range 45 → 94 gallons
• Certified storage volume: 24% · range 36 → 82 gallons

Gas Tankless Water Heaters

• Uniform energy factor: 34% · range 0.95 → 0.98
• Maximum flow: 32% · range 3.8 → 6 GPM
• Minimum activation flow: 18% · range 1 → 0.1 GPM
• Connected capable: 16% · yes/no