One method of producing hot water for domestic use in a home is via a gas fired water heater. The water is heated in much the same way as a pot of water is heated on a gas
stove. Every gas fired water heater must be installed in a safe manner and must be installed with a provision to discharge the products of combustion from the burning gas. Discharge of the products
of combustion is via a metal flue pipe which is highlighted in the photo. The purpose of the flue pipe is to harmlessly direct and discharge the toxic flue gasses into the chimney. These combustion
gasses contain toxic carbon monoxide.
Hot air rises, therefore, the flue pipe must rise upward towards the chimney to discharge the hot combustion gasses, the vent pipe must not slope
downward. Flues that slope downward cause the discharge of toxic carbon monoxide into the areas surrounding the water heater. Conditions such as this require prompt repair.