| Anode Rod: A sacrificial rod made of aluminum or magnesium with a steel core designed to protect the tank from rusting. The rod attracts corrosive elements, therefore deteriorating over time instead of the tank. |
| Anti-Scald Valve: A device that mixes cold water with the outgoing hot water to ensure that the water reaching the faucet is at a safe temperature. |
| BTU (British Thermal Unit): The amount of heat energy required to raise the temperature of one pound of water by one degree Fahrenheit at sea level. |
| Check Valve: A valve that allows water to flow in one direction but prevents it from flowing in the opposite direction. |
| Circulating Pump: A device that moves hot water from the heater to fixtures and appliances, and then returns cooled water back to the heater. |
| Closed System: A water heating system where the water is reheated and recirculated within the system rather than being drained away. |
| Combustion Chamber: The part of a gas water heater where the burner heats the heat exchanger, which in turn heats the water. |
| Condensing Water Heater: This type of water heater uses the heat from the exhaust gases to further heat the water, increasing efficiency. |
| Corrosion: The gradual destruction of metal by chemical reactions, often a significant issue in water heaters due to the constant contact with water. |
| Desuperheater: A device that uses waste heat from an air conditioner, heat pump, or geothermal system to heat water. |
| Dip Tube: The tube inside a water heater tank that lets cold water flow from the top of the tank to the bottom, ensuring that the water gets heated evenly. |
| Direct Vent: A type of venting system that draws air for combustion from outside and exhausts combustion gases directly outside. |
| Drain Valve: A valve located near the bottom of the water heater that allows for the tank to be drained during maintenance or replacement. |
| Drain-Water Heat Recovery: A system that captures heat from the hot water that goes down the drain and uses it to preheat incoming cold water, improving efficiency. |
| Efficiency Rating: The measure of a water heater’s overall energy efficiency. It is determined by comparing the energy supplied in heated water to the energy input of the water heater. |
| Energy Factor (EF): This metric measures a water heater’s overall efficiency by comparing the amount of hot water produced per unit of fuel consumed over a typical day. |
| Expansion Tank: A tank used to protect closed water heating systems and domestic hot water systems from excessive pressure. The tank contains air and water separated by a diaphragm. |
| First Hour Rating (FHR): A measure of how much hot water a heater will deliver during a busy hour (such as first thing in the morning). It is calculated by adding the amount of hot water in a tank to the amount of incoming cold water that can be heated in an hour. |
| Flow Rate: The speed at which water can move through a system, usually measured in gallons per minute (GPM). |
| Flue: A passage that allows combustion gases from the water heater to be vented outside. |
| Gas Control Valve: A device that controls the flow of gas to the burner in a gas water heater. |
| Gravity System: A type of hot water system where hot water rises naturally without the need for pumps. |
| Heat Exchanger: A device that transfers heat from one source (like a burner) to another source (like water) without the two ever coming in direct contact. |
| Heat Pump: A type of water heater that uses electricity to move heat from one place to another instead of generating heat directly, which can be more energy-efficient. |
| High-Efficiency Water Heater: A water heater model designed to operate at a higher energy factor, and therefore be more cost-effective, than standard models. |
| Hot Water Return Line: In a circulating system, the pipe that brings cooled water back to the heater to be reheated. |
| Hybrid Water Heater: A water heater that combines the technology of tank and tankless models or a heat pump system with a traditional storage tank. |
| Hydrogen Sulfide: A compound often responsible for a “rotten egg” smell in water, which can cause corrosion in a water heater. |
| Immersion Element: A device that is immersed in the water in the tank and heats it directly. |
| Indirect Water Heater: A water heater that utilizes the home’s space heating system to heat the water. |
| Insulation: Material used to reduce heat loss in a water heater. |
| Low NOx (Nitrogen Oxides): An environmental standard for water heaters that emit low levels of nitrogen oxides, which contribute to smog. |
| Mixing Valve: A valve that mixes hot water with cold water to ensure safe, consistent water temperature at the faucet. |
| Multi-Point Water Heater: A water heater that is designed to supply hot water to multiple fixtures simultaneously. |
| On-Demand Water Heater: Another term for a tankless water heater, which heats water as it is needed rather than storing hot water in a tank. |
| Oxygen-Depletion Sensor (ODS): A safety device on certain gas water heaters that shuts off the gas supply if the oxygen level in the room falls too low. |
| Pilot Light: A small gas flame that ignites the gas burner in a water heater. |
| Point-of-Use Water Heater: A compact water heater designed to supply hot water to a specific application, like a sink or shower, located close to the use point to reduce the wait time for hot water. |
| Recovery Rate: The amount of water in gallons that a water heater can heat in one hour, starting with cold water. |
| Relief Valve: A safety device that releases pressure if the pressure or temperature inside the tank gets too high. |
| Retrofit: The modification of a water heater system to improve energy efficiency. |
| Scale: A buildup of minerals, usually calcium or magnesium, on water heater elements and the interior of the tank. |
| Sealed Combustion: A type of combustion system that takes in outside air for combustion and vents combustion gases directly outside. |
| Sediment: Mineral deposits that naturally occur in water and can build up in the bottom of a water heater tank, potentially leading to issues with water heater performance. |
| Shut-Off Valve: A valve that allows the water supply to be cut off, often used during maintenance or repairs. |
| Solar Water Heater: A system that uses energy from the sun to heat water. It usually involves solar collectors and a storage tank. |
| Stagnant Water: Water that is allowed to sit in pipes or a tank without being circulated or heated, potentially leading to bacterial growth. |
| Standby Heat Loss: This is the energy wasted to keep a tank full of hot water at the ready, even when it’s not being used. |
| Tankless Water Heater: A type of water heater that heats water directly without the use of a storage tank. |
| Thermal Expansion: The increase in water volume that occurs as it is heated in a closed system, which can lead to increased pressure. |
| Thermocouple: A safety device that shuts off the gas if the pilot light goes out. |
| Uniform Energy Factor (UEF): It’s a newer, standardized metric that more accurately represents a water heater’s efficiency by categorizing the water heaters into four different classes each with its own UEF metrics. |
| Vacation Mode: A setting on some water heaters that maintains a lower water temperature while you are away to save energy, while preventing the water from freezing. |
| Venting: The process of removing by-products of combustion (like carbon dioxide and water vapor) out of the home. |
| Water Hammer: A loud noise that occurs when the flow of water is suddenly shut off, causing the pipes to bang against the wall or each other. |
| Water Heater Blanket: An insulating cover that can be wrapped around a water heater tank to reduce standby heat loss. |
| Water Pressure: The amount of force that water has when moving through pipes. |
| Watt: A unit of power used to measure the heating power of an electric water heater. |
| Wi-Fi Connected Water Heaters: Modern water heaters that can be controlled remotely using a smartphone app, providing data on usage and allowing for remote adjustments. |
| Zone System: A heating system where different areas (or “zones”) can be set to different temperatures. |