> I wish I knew a site like this on every subject.

For water heaters, this was helpful to me once: http://waterheatertimer.org

It is not a pretty site (author only knows of HTML tables?), but for me it fulfilled the:

> Somebody took a whole lot of know-how about [x], organized it, published it online

The site at first looks like just affiliate links, but has a lot of useful info buried like:

http://waterheatertimer.org/How-it-works.html

http://waterheatertimer.org/How-to-troubleshoot-electric-pro...