I am a new owner of an old (1944) house.
I have forced hot air. I can't for the life of me find the air intake. I was told to look for a large grate, about twice the size of all of the other house grates, however none are that large. Moreover, they all seem to be blowing out hot air. There is a vent very close to my heating unit in the basement, but luckily that one also seems to be blowing out air, or that would be really bad (stale basement air as air intake, very poor house circulation).
I had a guy over who used to contract (for a different reason, he was not there to look for this problem), and after a quick look, he suggested during a renovation some prior owners may have drywalled over it.. that sounds like a horrible thing to do.
Is there a way I can systematically find my air intake? At this point I'm going to have to light an incense and stick it near each vent or something. And what if I don't have one?
OK! I did the incense test and have good news and maybe bad news. The good news is that, unless I'm reading the "incense flow" wrong, every room has an output and an input. One vent in each room appears to be blowing hot air out, and one vent in each room appears cold to the touch and incense flows in.
The bad news is that there also appears to be a return vent right in the basement where the furnace is: http://imgur.com/a/5qXCv. Wouldn't that be recycling nasty dirty basement air and then pushing it out into the house?