im asuming you have a hot air furnace...you will need to find the area where your air filter is an its probably in that area and your in no danger, it can get to the burner area...if you cant find the filter, call an hvac tech...good luck
My dog was playing with a tennis ball and the ball accidentally fell inside of the regular vents that go to the gas furnace and I'm pretty scared of what could happen if its not removed. I can hear the ball jump up and hit the top of the aluminum vent in my basement so I'm guessing there is some sort of gate that wont let the ball fall inside the gas furnace itself, but I'm still concerned! please help me!
The ball did not fall inside the cool air vent but the vent where the hot air comes out and I just went down stair and saw that the ball is basically on top of the furnace.
Here's a picture of how my furnace sort of looks like and I believe ball is right around where the darkest red arrow is in the picture.
http://www.thegasfurnace.com/wp-content/uploads/2009/12/Furnace.jpg
See if you can get your vacuum cleaner hose in far enough to suck it back. If not you could always get a pipe cleaning company to come in and clean the pipes for you. Who knows what else you might find. Hope this helps you and good luck.
Richard