I agree that you should call the dealer. They get paid to answer questions. You could have also just looked on line.
Scroll down to see the frame dimensions on these 2 links.
24 inch:
http://www.bernina.com/en-US/Product...FQeBaQodazoHgA
20 inch:
http://www.bernina.com/en-US/Product...g/BERNINA-Q-20
You need at least 3 feet in front of the frame and if you are going to do pantos, you need 3' in back too. You probably want at least 2' in back to allow for the machine movement. You also need 3 feet on the side with the cranks.