Actually, a chimney isnt required. Locate your window, and build your cooking hob, JUST BELOW the window. The window sill, being 2ft ABOVE the gas hob. ALL YOUR FUMES WILL RISE UP AND VENTILATE THROUGH THE WINDOW.
Always not possible.. especially if following vaastu..which dictates east facing while cooking. Many a time the window might be on some other wall. Then the chimney is the only solution