If I close my bathroom door and then turn on the ventilation fan, the air being sucked out of the heating vent has a crawlspace odor (I've been down there many times, so I recognize the smell).
I suspect there is a leak in the heating ducts in the crawlspace. However, when I went down there to take a quick look around, I didn't see anything obvious.
Is there a good way to locate the leak(s) quickly? I thought about injecting smoke into the heating system and look for the smoke in the crawlspace. But that would also fill my house with smoke. I suppose I could turn on the heat and go over every inch of ducts in the crawlspace to feel for warm air, but this could take a long time and I may not catch all the leaks.