When gas-fired water heater exhaust fumes spill back into the water heater or home. Backdrafting can present a very serious hazard for your home and your family. Melted plastic on the draft hood, moisture on top of the hot water storage tank, and corrosion on top of the tank are all signs of backdraft. Causes of backdraft include (but aren’t limited to) lack of a draft hood, sharp turn at the draft vent, or bent vent connectors.


Component inside of gas-fired water heaters that produce a flame. In gas-fired tank-type heaters, the burner heats the hot water storage tank; in tankless water heaters, the burner heats the heat exchanger.

Circulation Pump

A closed-loop plumbing system that recirculates warm water throughout a home. Along with point-of-use water heaters, circulation pumps are a solution for large homes in which it takes a long time for hot water to reach appliances and fixtures located far away from the water heater.

Cold-Water Inlet Pipe

Pipe that carries cold water into a water heater system.

Cold-Water Valve

Valve that switches the cold-water inlet pipe on and off.

Dip Tube

Pipe that deposits cold water into the hot water storage tank.

Draft Hood

Round, funnel shaped piece of metal that wraps around the vent pipe above gas-fired water heaters. Draft hoods prevent combustion exhaust from spilling into the home or back into the water heater.

Drain Cock

Water spigot located at the bottom of hot water storage tanks used to flush the tank.

Electrical Resistance Heating Elements

Rods inside of electric tank-type water heaters that convert electrical energy into heat.

Flow Sensor

Sensor inside of tankless water heaters attached to the cold-water inlet pipe. Flow sensors turn on the tankless water heater system when they detect cold water flowing into the system.

Flue Baffle

Tube that runs from the burner to the vent of gas-fired tank-type water heaters that helps remove exhaust and by-products that result from the combustion process.

Gas Control Valve

Valve attached to gas pipe that turns the flow of gas on or off.

Heat Exchanger

Component of tankless water heaters that heats up cold water by means of a heating coil.

Hot-Water Outlet Pipe

Pipe that carries hot water out of the water heater and into the home’s hot water pipes.

Hot Water Storage Tank

Cylindrical tank, typically made of steel and lined with glass, that stores hot water in tank-type water heaters.

Lag Time

Time it takes for hot water to reach the appropriate appliance or fixture.

Pilot Light

Component of gas-fired water heaters that ignites the burner.

Point-of-Use Tankless Water Heaters

Tankless water heaters that attach directly to a fixture or appliance. Often used in large homes where lag time is an issue. Can also be used for appliances or fixtures that aren’t attached to the home’s hot water system.

Sacrificial Anode Rod

Magnesium rod found in tank-type water heaters that corrodes in place of the tank or other internal components. Anode rods should be inspected about once a year and replaced once they have fully corroded.

Supply and Delivery Pipes

General term for both cold-water inlet pipe and hot-water outlet pipe.

Tank Water Heater

A type of water heater that includes a hot water storage tank.

Tankless Water Heater (Also known as Instantaneous or On-Demand Water Heaters)

A type of water heater that does not include a hot water storage tank. Instead, tankless water heaters heat water as it passes through a heat exchanger. High-end gas-fired tankless water heaters have minimal lag time, which is why they are often referred to as ‘on-demand’ or ‘instantaneous’.

Thermostatic Mixing Valve

Valve that prevents scalding by adding cold water to a stream of hot water.

T&P Deposit Pipe

Pipe that releases water when the pressure or temperature inside of a hot water storage tank is too high. T&P deposit pipes typically run alongside the tank and end about six inches above the floor of the home.

T&P Valve

Safety valve located at the top of hot water storage tanks. This valve monitors pressure and temperature in the tank. The valve will expel water through the T&P deposit pipe when the pressure or temperature within the tank is too high.

Water Heater Exhaust Vent

Vent found coming out of gas-fired water heaters that carry combustion by-products outside of the home.

Water Heater Thermostat

Device that sets and regulates temperature. In tankless water heaters, the thermostat regulates the temperature of the water leaving the tank; in tank-type water heaters, it regulates the temperature of water within the tank.