United States
Registry filings from the U.S. Department of Energy, priced with the tariff your own utility charges.
The first category
Water heaters. The coverage denominator is the Department of Energy's Compliance Certification Database: every basic model manufacturers have on file for the category, across all types — electric storage, gas storage, tankless, heat pump — rather than a shortlist.
Heat pump water heaters are not a separate record type in that database. They are a segment computed from the Uniform Energy Factor a model files. Where this site describes one, it says which threshold it used.
What a page will carry
The annual running cost for a model, computed from the energy figure in its registry filing and the tariff schedule its owner's utility publishes; the same figure over the life of the appliance; and the source and pull date for both inputs. Where the registry does not publish something — warranty terms, physical dimensions for many models, noise — the page says so rather than estimating it.
Not published yet
What is missing: model, comparison and cost pages for this market.
Why: each one waits on a live registry pull and a live tariff lookup. Neither is wired up yet, and a cost page without them would be a guess with a citation stapled to it.
What is here instead: the scope statement above, so that when the pages arrive you can check them against what was promised before they existed.