Test and data
What the values on this site are, where they come from and how they were cleaned. Each definition lives here once; the other pages link back.
Where the numbers come from
Every model on this site comes from the U.S. EPA dataset “ENERGY STAR Certified Water Heaters” (data.energystar.gov, dataset pbpq-swnu), rows updated October 27, 2026 and read on October 28, 2026. The values in the dataset are the results of the Department of Energy test for water heaters (10 CFR Part 430, Subpart B, Appendix E), as certified by the listing companies. We do not test anything ourselves.
The list covers certified models only. Standard electric-resistance tanks, most atmospheric gas tanks and electric tankless heaters are not certified and do not appear. Counts on this site therefore read “of the certified models listed here”, never “of all water heaters”. The site covers the US market: 179 rows marked for Canada only were left out.
How to read a page
Type and maker pages open with the facts that set that group apart, then one chart, then a table with one row per rating set. Inside each row, the model numbers sit behind a “model numbers” toggle, grouped by brand. Notes in copper italics under a set name mark a record that the opening paragraph does not already state.
Rating sets
Many heaters are sold under several brand names with identical certified values. A rating set groups model numbers whose category, heat-pump subtype, draw pattern, rated volume, first-hour rating, max flow, UEF or solar UEF, annual energy and gas input are all the same. The 1,138 model numbers on the list form 187 rating sets. The key is exact: two sets that differ by 1 kWh/yr are separate sets.
Ranks (“the 2nd highest of 58”) count rating sets, so a design sold under eight names counts once. Shares (“88% of model numbers”) count model numbers. Medians on this site are taken over rating sets, again so that each distinct heater counts once. Ranks are competition ranks: tied sets share a rank, and the text says how many are tied.
An asterisk (*) in a model number is the listing’s wildcard for a variant character, such as a color or a fuel letter. Model numbers keep it; names in running text drop it.
The measures
- First-hour rating
- Gallons of hot water a storage heater delivers in one hour of the DOE test, starting from a full, heated tank and counting the water it reheats during that hour. Storage types only.
- Max flow at a 67 °F rise
- The flow a tankless unit sustains in the DOE test while heating 58 °F water to 125 °F. It is not the brochure flow at a smaller rise, and it is never compared with a first-hour rating.
- Rated volume
- The storage volume measured in the test, not the nominal size on the label; a heater sold as 50 gallons often rates 45 to 47.
- Draw pattern
- The DOE usage profile the UEF test uses, set by the first-hour rating (below 18 gal very small, 18 to under 51 low, 51 to under 75 medium, 75 or more high) or, for tankless units, by max flow (below 1.7, 1.7 to under 2.8, 2.8 to under 4, 4 gal/min or more). All 1,138 kept models match these bins.
- UEF
- Uniform Energy Factor: hot-water energy delivered divided by energy used over the 24-hour test. Comparable only within one draw pattern. A heat-pump UEF and a gas UEF are on different scales and are never compared as a ratio.
- Annual energy
- kWh per year (heat pumps) or therms per year (gas) at the test conditions for the model’s draw pattern. It is not a forecast for any household and is never converted into money.
- Solar UEF
- The solar uniform energy factor from the SRCC OG-300 rating, as reported in the dataset. A usable value survives for 27 solar sets; we show the values but do not rank them.
- Compressor cut-off
- The lowest air temperature at which a heat pump’s compressor still runs, as listed. A set shows a value only when all its model numbers list the same one; 90 of the 101 heat-pump sets do.
- First-hour output per rated gallon
- Our own index: first-hour rating divided by rated volume, for storage heaters. It shows how far a heater’s first hour reaches beyond its stored volume. It is not a DOE or ENERGY STAR figure.
- Partner
- The company named as ENERGY STAR partner on the listing, that is, the company that certified the model. It says nothing about who owns a brand or builds a heater; we write “listed by”, never “made by”.
Cleaning rules
Each rule sets an implausible value to empty. If that leaves a core value empty, the model is dropped (next table). Counts are rows of the source file.
| Rule | Rows |
|---|---|
| Storage volume of 0 or 1 gal (placeholder on tankless rows) set to empty | 242 |
| Tank height or diameter of 0 or 1 in set to empty | 214 |
| Solar UEF of 50 or more set to empty (99 is a repeated placeholder) | 27 |
| Tankless max flow that needs more heat than the listed gas input supplies: flow and input set to empty | 23 |
| Heat-pump compressor cut-off of 1 °F (a repeated placeholder) or outside −40 to 70 °F set to empty | 110 |
| Gas use below 50 therms/yr set to empty | 2 |
| Recovery efficiency outside a plausible range set to empty (heat pump and gas) | 27 |
| Reason | Rows |
|---|---|
| Canada-only market | 179 |
| Solar: no usable solar UEF after the placeholder rule | 27 |
| Tankless: max flow and input voided by the energy-balance rule | 23 |
| Exact duplicate rows | 3 |
| Gas: no usable gas use | 2 |
| Other missing core values | 2 |
One effect worth knowing: the compressor cut-off rule removes most values on the CO2 split systems listed by the A.O. Smith Corporation, where “1 °F” appears as a placeholder. The energy-balance rule removes a block of propane tankless versions whose listed flow is higher than their listed input could supply.
What this site does not do
No prices, operating costs or financial incentives, and no sizing advice: the site reports certified test values and compares them where the test allows. It is not affiliated with or endorsed by EPA, DOE or ENERGY STAR and uses no ENERGY STAR mark.
Licence and attribution
The EPA data license states that EPA data is by default in the public domain and gives no warranty for accuracy. Attribution as used in every footer: “Data: U.S. EPA ENERGY STAR Certified Water Heaters dataset (data.energystar.gov, pbpq-swnu), certified models as of 2026-10-27. This site is not affiliated with or endorsed by EPA or ENERGY STAR.”