Disclosure

How this site is funded

It is not. There are no affiliate links, no advertising, no sponsored content and no paid placements anywhere on this site. No manufacturer or retailer has paid for a mention, and none has been offered one.

If that ever changes, this page changes with it, and any page carrying a paid link will say so before you reach the link.

What has been tested

That is why there are no scores, no star ratings and no "best" lists. A ranking implies a comparison that has not happened. What the site does instead is tell you the number your room needs, and which units claim to meet it.

Where the numbers come from

Two kinds. Figures computed by this site, from daily weather readings it stores and processes, which say so and show the range they cover. And figures taken from somewhere else, which name the source and the date it was read.

Where a figure is provisional, meaning the method is sound but the underlying coefficient has not yet been checked against a published source, the page says so in plain words rather than in a footnote. Treat anything marked that way as a size band rather than a specification.

When this site is wrong

It will be, sooner or later. Planning law changes, price caps move and manufacturers revise their specifications. Corrections are made on the page that was wrong, and anything with a legal or safety consequence carries the date it was last checked.