Gas Hot Water System: How Does Instantaneous Hot Water Work?
How does a gas hot water system work?
An instantaneous hot water works by heating the water as it passes through the unit.
Also called an LPG instantaneous hot water system, an instantaneous hot water heater is the most popular type of gas hot water system in Australia.
The reasons are simple — an LPG instantaneous hot water system never runs out of hot water and they are energy efficient.
But how does a continuous hot water system work?
How Does a Gas Hot Water System Work?
An LPG instantaneous hot water works when you open a hot water tap and a sensor detects the water flow.
When the continuous hot water system is working, the gas burner fires and the heat exchanger works to heat the water. See image.
Some models of tankless LPG instantaneous hot water work with a secondary heat exchanger to pre-heat the water, using heat from the continuous flow hot water heater exhaust gases.
A thermostat works to regulate the amount of gas that goes to the gas hot water system burner, maintaining the pre-set water temperature.
The gas burner fires and the heat exchanger warms the flowing water.
Computer Controlled Gas Hot Water System
At the heart of an LPG instantaneous hot water system is an Electronic Control Unit (ECU) that controls how the gas flows through the continuous hot water system.
The ECU controls all of the functions of a modern gas hot water system, including temperature control, ignition, gas flow, and modulation.
It is also responsible for safety, with a flame sensor and automatic gas cut-off in the event of a problem.
Gas Hot Water System Getting Started
When you turn on a hot water tap anywhere in your home, a flow sensor connected to the ECU detects the water flow through the gas hot water system, and the heating begins.
A slow leaking tap is not enough flow to start the gas hot water system.
However, leaky water pipelines and continuous hot water system repairs require immediate inspection.
Some LPG instantaneous hot water system models have a combustion fan that draws air for combustion.
At the same time, the ECU starts the gas flow via a solenoid gas valve and triggers the igniter.
The igniter sparks until the flame sensor detects a flame.
If the gas flow fails to light within a few seconds, the ECU shuts down the flow to prevent any unsafe accumulation of gas.
The LPG Instantaneous Hot Water System Process
In an LPG instantaneous hot water system, the gas burner applies heat to the heat exchanger that the water flows through.
The course of the continuous hot water system is typically a serpentine pattern, allowing the water to absorb as much heat as possible from the walls of the heat exchanger.
Some instantaneous hot water models have a secondary heat exchanger to pre-heat the water, using the heat from the burner exhaust gases.
This is often called a “condensing” continuous hot water system model.
The advantage of these gas hot water heaters is that they provide even greater energy efficiency; however they tend to have a higher purchase price than standard instantaneous hot water heater models.
Many non-condensing continuous hot water system models are already 6-star rated.
Controlling the Temperature of a Continuous Flow Hot Water Heater
As the flow rate and temperature of the incoming water can vary, the ECU modulates the amount of gas that goes to continuous hot water system.
This modulation of the gas keeps the instantaneous hot water system at a constant temperature.
This functionality is based on a water temperature sensor on the exit side of the heat exchanger.
Some instantaneous hot water heaters have temperature controllers that allow the user to select a temperature and others are factory pre-set.
These controllers can be located on the flow-through gas hot water system or wired to a remote location like a kitchen or bathroom.
The ECU takes the controller’s input to modulate the gas flow, keeping the continuous hot water system at the user’s desired temperature.
Most models of instantaneous hot water come with their maximum temperature pre-set in the factory.
This is a safety precaution to help prevent possible scalding.
Gas Hot Water Tank
Different from an LPG instantaneous hot water system, a gas hot water tank works by heating water and storing it until needed.
Hot water is drawn from the top of the gas hot water tank and replaced with cold water at the bottom because warm water rises.
When the gas hot water tank water temperature drops below the thermostat set point, the gas hot water tank works by having the burner run until the temperature recovers to the set point.
Power Supply to an LPG Instantaneous Hot Water System
To power the flame igniter, most instantaneous hot water units are connected to your home’s power supply.
However, there are some LPG instantaneous hot water units that use energy created by the water flowing through a small water turbine to provide the power for ignition (see graphic).
Lastly, there are also some continuous hot water system units that just use a simple battery.
The turbine and battery powered continuous hot water system units have a distinct advantage over the connected models, inasmuch as they will operate even during a power outage.
The disadvantage of the turbine powered continuous hot water system is that the entire unit is physically larger than a comparable plug-in model, as well as more expensive.
How a Gas Hot Water System Works – Summary
Cold water flows into the tankless gas hot water system when a hot water tap is opened inside your home.
The water flow is detected by an instantaneous hot water sensor that ignites the gas burner, to heat the water in the heat exchanger.
The water typically follows a serpentine pattern through the continuous hot water system heat exchanger, absorbing as much heat as possible.
An electronic control unit modulates the gas burner to maintain a set water temperature.
This is the simple explanation of how does a gas hot water system work.
Many Manufacturers & Models of Gas Hot Water System
Please note that there are many manufacturers and even more models of gas hot water system, including both LPG and natural gas.
Therefore, there can be variations in features, functionality and operation from the general gas hot water system descriptions provided above.
You should always consult the specific manufacturer’s information when making a gas hot water system purchase selection or other decision.
You should also always consult your owner’s manual for advice on safe gas hot water system operation and maintenance.