When the furnace really stops heating
 

- you have a crawl space

- you find duct cut open

- you smell Pot

_ and find beer cans

"YELM, Wash., Jan. 9 (UPI) -- A Washington state woman said a
repairman examining her furnace discovered someone had been living in
the crawlspace beneath her home."

http://www.upi.com/Odd_News/2013/01/09/Repairman-finds-crawlspace-occupied/UPI-59811357764506/#ixzz2HbjpAD00