Every 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. Water heaters are ranked within their nominal tank size (40–50, 65 and 80 gallons).
| Factor | Measures | Weight |
|---|---|---|
| Efficiency | certified Uniform Energy Factor | 35% |
| Hot water | certified first-hour rating, for its size | 20% |
| Warranty | tank, parts and labor cover | 20% |
| Cold rooms | lowest room temperature the heat pump runs in | 15% |
| Noise | sound level while the heat pump runs | 10% |
Where the numbers come from
The Uniform Energy Factor, first-hour rating, yearly energy use, measured tank volume, compressor cut-off temperature and, where given, sound level are DOE test results published in ENERGY STAR’s certified heat pump water heater data. Each product page links its listing. The warranty, circuit, backup element, room size, weight and features come from the maker’s spec sheet, installation manual or warranty terms.
Many brands sell the same water heater under their own names, so identical certified numbers across brands are expected. Each product page lists the twins it found (“Also sold as”). The warranty, where it’s sold and who supports it can still differ.
The factors
Efficiency is the certified Uniform Energy Factor (UEF): how many units of heat reach the water for each unit of electricity, over a standard day of use. A standard electric tank rates a little under 1. A UEF of 3.0 scores zero and 4.4 full marks.
Hot water is the certified first-hour rating: how many gallons of hot water the heater delivers in an hour starting with a full tank. It shows whether a tank keeps up with back-to-back showers. A bigger tank always delivers more, so each size has its own scale:
| Size | First-hour rating, scoring 0 → 100 |
|---|---|
| 40–50 gallons | 50 → 75 gallons |
| 65 gallons | 60 → 85 gallons |
| 80 gallons | 75 → 100 gallons |
Warranty combines the tank warranty (45%: 6 years scores zero, 12 years full marks), the parts warranty (40%: 3 years scores zero, 10 years full marks) and any labor cover (15%: none scores zero, 3 years full marks). A heat pump has a compressor, fan and controls that a plain tank doesn’t, so parts cover matters as much as the tank. A term the maker doesn’t state counts as the neutral middle, and the factor is marked estimated.
Cold rooms is the lowest room temperature at which the heat pump keeps running before the heater switches to its backup element, which uses three to four times the electricity. It decides whether an unheated garage or basement works through the winter. The certified compressor cut-off is used; where ENERGY STAR lists none, or one that can’t be right, the maker’s stated operating minimum is used and the factor is marked estimated. 45 °F scores zero and 20 °F full marks.
Noise is the sound level while the heat pump runs, from ENERGY STAR where listed, otherwise from the maker: 56 dB(A) scores zero and 40 dB(A) full marks. It matters most for a heater near a bedroom or living space.
What isn’t scored
Price. Most heat pump water heaters are sold through Home Depot, Lowe’s and plumbing suppliers, whose prices couldn’t be checked and change often with rebates. Prices are shown where they could be checked, with the date, but a model without one isn’t marked down. Utility rebates and the federal tax credit also change the real cost a great deal from one home to the next.
Yearly energy use (kWh) is shown but not scored, because ENERGY STAR tests each model under one of two draw patterns depending on its first-hour rating, so the figures only compare between models with the same pattern. UEF is the like-for-like measure.
120 V or 240 V is shown and filterable but not scored. A 120 V plug-in model avoids new wiring; a 240 V model recovers faster.
Wi-Fi, a demand-response port, leak detection and modes are listed but not scored. Independent tests are rare for these products, so none are scored.
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 size. Discontinued models stay listed but rank below every current model and can be hidden with the “Hide discontinued” filter.