The one in the tenants place is getting really bad. The quote for a new
system from the pros was multiple kilodollars. There's an ad in the local
bargain hunter for one; I called, and a guy with a thick middle-eastern
(greek?) accent told me a _very_ nice price to "get it out of his garage".
Said it was pulled from his house working, drained, and put in the garage.
Was used about two years, or maybe that was it was pulled two years ago -
very thick accent.

This is an oil-fired hot-water furnace.

Now I'm a mechanical guy, and furnaces can't be all that complicated, but
I've never looked at one before. What should I be looking for and asking
questions about? For his price I'm won't be making a big mistake, but it
would be nice to know more than I do before I go over there.

Um, it's made of metal. That counts, eh?