With HVAC, we have a lot of potential tags, so before taking my own guess at what the wiki's should say, I thought I'd solicit the group. Here's a list of the current tags that I think could use some clarification, and my best guess of how we should be using them:
If everyone is in agreement with this, then I can start by updating the wiki's to help differentiate the furnace from the central heating system, and the air conditioner from air conditioning, etc. Then I'll slowly retag some of the older questions (so that new questions aren't lost in a sea of edits). Of course any help is always appreciated.