A

AFUE (Annual Fuel Utilization Efficiency)

A measurement of the annual efficiency with which a water heater converts fuel into usable hot water.

Anode Rod

A sacrificial metal rod that protects the inner tank from corrosion.

Altitude Adjustment

A calibration that compensates for reduced oxygen levels at higher altitudes, ensuring optimal combustion.

Anti-Scald Valve

A temperature control device that prevents excessively hot water from reaching taps.

B

BTU (British Thermal Unit)

The standard unit for measuring heating capacity; higher BTU indicates higher heating power.

Burner

The component where gas mixes with air and ignites to heat the water.

Bypass Valve

A valve allowing water flow to be redirected for maintenance or circulation adjustments.

C

Carbon Monoxide (CO)

A byproduct of incomplete combustion; modern systems include sensors and safety cutoffs to prevent CO hazards.

Combustion Air Supply

The air required for the gas to burn efficiently; improper supply reduces performance and increases emissions.

Combustion Chamber

An enclosed space where fuel and air mix and ignite to produce heat.

Condensing Technology

Captures and reuses latent heat from exhaust gases, improving energy efficiency by up to 15%.

Controller Board (PCB)

The electronic board that manages ignition, gas flow, safety sensors, and user settings.

D

Direct Vent System

A sealed combustion system that draws air from outside and exhausts flue gases outdoors.

Dip Tube

Delivers incoming cold water to the bottom of the tank for efficient heating.

Draw Efficiency

Indicates how effectively a heater can supply hot water under continuous use.

E

Energy Factor (EF)

An earlier efficiency rating replaced by UEF; it measures daily energy consumption versus output.

Electronic Ignition

A modern ignition system that replaces the standing pilot, improving efficiency and safety.

Exhaust Fan

A fan-assisted system that ensures safe removal of combustion gases and supports variable flue designs.

Expansion Tank

Absorbs pressure fluctuations due to thermal expansion of water.

F

Flame Sensor

A safety device that detects the presence of a burner flame and stops gas flow if no flame is present.

Flue Pipe

The exhaust passage that channels combustion gases out of the building.

Flow Rate

The amount of hot water delivered per minute, measured in liters per minute (L/min) or gallons per minute (GPM).

Fuzzy Logic Control

A control algorithm that adjusts combustion parameters dynamically based on load and temperature.

G

Gas Pressure Regulator

Controls the gas pressure entering the water heater for stable combustion.

Gas Valve

Regulates the volume of gas supplied to the burner according to demand and safety input.

GPM (Gallons Per Minute)

Measures the water heater’s output capacity.

Gas Conversion Kit

A set of parts used to convert between natural gas and LPG (liquefied petroleum gas) operation.

H

Heat Exchanger

Transfers heat from combustion gases to the water, typically made of copper, stainless steel, or aluminum alloy.

Heat Load

The total thermal energy required to raise water temperature to a desired level.

Hydraulic Block

The water circuit assembly that integrates valves, sensors, and flow regulators.

I

Ignition System

Mechanism that initiates combustion — includes spark ignition, hot surface ignition, or direct ignition.

Inlet Gas Pressure

The measured pressure of gas entering the heater, crucial for correct combustion performance.

Ionization Electrode

Detects and confirms flame presence for safety interlock.

L

Low NOx Burner

A burner design that minimizes nitrogen oxide emissions through advanced air–fuel mixing.

Load Compensation

The ability of the system to adjust heating output based on varying water flow or demand.

M

Manifold Pressure

The pressure of gas distributed to the burners, adjusted for optimal performance.

Modulating Gas Valve

A valve that adjusts gas flow proportionally to demand for steady temperature control.

Mixing Valve

Combines hot and cold water to reach a target outlet temperature.

O

Oxygen Depletion Sensor (ODS)

A safety sensor that shuts down the heater when oxygen levels drop below safe thresholds.

Open Flue System

A venting system that relies on natural draft to remove combustion gases.

P

Pilot Light

A small flame used to ignite the main burner in older systems.

Pressure Relief Valve (TPR Valve)

Prevents excessive pressure buildup in the tank by releasing water automatically.

Primary Heat Exchanger

The main unit responsible for transferring heat from the burner to the water.

Pulse Combustion Technology

An advanced heating method that increases efficiency and reduces noise by using controlled combustion pulses.

R

Recovery Rate

The speed at which a heater can reheat water after it has been depleted, measured in gallons per hour (GPH).

Recirculation System

A design that keeps hot water moving through the plumbing system, reducing wait time at taps.

S

Sealed Combustion System

Isolates the combustion process from indoor air, improving efficiency and indoor safety.

Secondary Heat Exchanger

Used in condensing models to extract additional heat from exhaust gases.

Smart Controller

A digital interface that allows temperature adjustment, diagnostic monitoring, and Wi-Fi connectivity.

Safety Interlock System

A combination of sensors and relays that prevent unsafe operation if any component fails.

Stack Temperature

The temperature of gases leaving the flue; an indicator of efficiency and combustion quality.

T

Tankless Water Heater

Heats water on demand without storing it in a tank, reducing standby heat loss.

Thermocouple

Detects flame presence and stops gas flow when no flame is detected.

Thermostat

Regulates burner operation to maintain set water temperature.

Thermal Efficiency

The ratio of heat output to total fuel energy input, often above 90% in condensing models.

Turbo Fan System

A fan-assisted combustion system that supports horizontal venting and consistent airflow.

U

UEF (Uniform Energy Factor)

The official DOE rating for efficiency, replacing EF, and providing realistic performance under various usage patterns.

Ultra-Low NOx

Refers to systems emitting extremely low nitrogen oxides, meeting stricter environmental standards.

V

Ventilation System

The assembly responsible for safe air intake and exhaust removal.

Variable Speed Fan

Adjusts exhaust airflow dynamically based on burner load and temperature.

W

Water Flow Sensor

Detects water movement and triggers the ignition system in on-demand units.

Water Pressure Regulator

Maintains consistent inlet pressure to protect internal components and ensure steady flow.

Warranty Period

Manufacturer’s coverage for replacement or repair, usually 5–10 years depending on component.

Wi-Fi Control Module

Enables remote monitoring, diagnostics, and operation via mobile applications.

Z

Zero Clearance Installation

A design allowing safe installation with minimal wall clearance.

Zero Cold Water Technology

Pre-heats water in the pipeline to eliminate initial cold bursts.

This glossary explains core concepts and technical terms related to design, efficiency, safety, and performance, providing a comprehensive reference for professionals involved in the manufacture, design, and distribution of gas water heaters.

For information on how these terms apply to our product line and manufacturing processes, please visit our Product and Technical Support section. Macro offers comprehensive OEM and ODM services for high-quality gas water heaters, designed to meet your needs throughout your entire partnership with us.