Sucky ducts

I've been gradually working on improving my home's energy efficiency. Today's rainy weather made for a good day to stay inside, so I decided to check the ventilation ducts. The house was built in 1971, and apparently whoever did the duct work was a lazy, drunken buffoon. It's surprising that any hot air made it all the way to vents. I went through a hell of a lot of tape and duct sealer putty.