An "H-style cap" is a chimney top constructed from chimney pipes shaped like the letter H. It is an age-old method of regulating draft in situations where prevailing winds or turbulences cause downdraft and backpuffing. Although the H cap has a distinct advantage over most other downdraft caps, it fell out of favor because of its bulky design. It is found mostly in marine use but has been regaining popularity due to its energy-saving functionality. The H-cap stabilizes the draft rather than increasing it. Other downdraft caps are based on the Venturi effect, solving downdraft problems by increasing the updraft constantly resulting in much higher fuel consumption.