Atmospheric water heaters, draft hooded,  with metal / steel pipe to a masonry chimney or B-vent chimney (also known as standard, conventional, normal, gravitational) have an exhaust pipe attached directly to the combustion area of the water heater. The exhaust gases leave the water heater through such exhaust pipe without the assistance of a powered blower fan. The method works because exhaust gases are warmer and therefore lighter than surrounding room temperature air and there is natural gravitational forces that push it upwards. This type of water heater works well only in certain configuration of the water heater space – when there is access to a relatively vertical exhaust pipe, or exhaust pipe with steep enough gradient to naturally extract exhaust gases outwards by just gravitational forces.