Having very long chapters upwards of 20 pages is actually detrimental for an average reader tires quickly and may not want to hold onto the book longer. What does that mean? He or she will never buy a novel or book written by you again, the last thing you need.
It is better to have 100 chapters of three pages each rather than 3 chapters of 100 pages each or 6 chapters of 50 pages each. The more the chapters your book contains the better, but for goodness sake, keep them short!