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How Does a Gas Water Heater Work? (How Instant Gas Geyser Works)

Tankless continuous flow through hot water heater systems are the most popular type of gas hot water heater. 

The reasons are simple -- they never run out of hot water and they are energy efficient. 

But how does a flow through hot water heater work (how instant gas geyser works)?

How Does a Gas Water Heater Work - Simplified Summaries

A tankless gas water heater works when you open a hot water tap and a sensor detects the flow. The gas burner fires and the heat exchanger warms the flowing water.

A gas water heater tank works by heating water and storing it until needed. Hot water is drawn from the top of the tank and replaced with cold water at the bottom, based on the fact that warm water rises. When the tank water temperaure drops below the thermostat set-point, the water heater works by having the burner run until the temperature recovers to the set-point.

How Does a Gas Flow Through Hot Water Heater Work - How Instant Gas Geyser Works

How Does a Gas Water Heater Work

A tankless gas continuous flow through hot water heater works (instant gas geyser works) when you open a hot water tap and a sensor detects the water flow.  When the flow through hot water heater is working (instant gas geyser working), the gas burner fires and the heat exchanger works to heat the water.

Some tankless instantaneous gas hot water systems work (instant gas geyser working) with a secondary heat exchanger to pre-heat the water, using heat from the flow through hot water heater exhaust gases.

A thermostat works to regulate the amount of gas that goes to the flow through hot water heater burner, maintaining the pre-set water temperature.

Continuous Flow Through Hot Water Heater - Tankless, Instant, or Instantaneous Gas Geyser?

Before we go further, let’s clear up the confusion on the terminology. People use all four terms to describe this type of instantaneous gas hot water systems, as all four expressions are very descriptive of this popular style of flow through hot water heater. 

But, no matter what you call them, they are great gas hot water systems.  

In fact, there are seven reasons that you should consider going with a tankless flow through hot water heater. 

Now, back to how they work…

Computer Controls How a Gas Flow Through Hot Water Heater Works

At the heart of most modern tankless continuous flow through hot water heaters is an Electronic Control Unit (ECU) that controls how the gas flow through hot water heater works (how instant gas geyser works).  The ECU controls all of the functions of the instantaneous gas hot water systems (instant gas geyser working) including temperature control, ignition, gas flow and modulation. 

It is also responsible for the safety aspects, with a flame sensor and automatic gas cut-off, in the event of a problem.

How a Tankless Gas Hot Water Systems Works (How Instant Gas Geyser Works) Getting Started

Tankless instantaneous gas hot water systems works (how instant gas geyser works) 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 hot water heater and the heating process begins.  Don’t worry, a slow leaking tap is not enough flow to start the unit and get the gas water heater working.

Some instantaneous gas hot water systems models have a combustion fan that draws in air for the combustion process. 

At the same time, the ECU starts the flow of gas and triggers the igniter. 

The igniter sparks until the flame sensor detects a flame. 

In the event that the flow through hot water heater fails to light within a few seconds, the ECU shuts down the gas flow to prevent any unsafe accumulation of gas.

Heating the Water in a Tankless Flow Through Hot Water Heater

The gas burner applies heat to the heat exchanger, that the water flows through in the flow through hot water heater, when the gas water heater is working (instant gas geyser is working). The course of the water is typically a serpentine pattern, allowing the water to absorb as much heat as possible from the walls of the heat exchanger as the water flows through the flow through hot water heater.

Some flow through hot water heater models have a secondary heat exchanger to pre-heat the water, using the heat from the burner exhaust gases. 

This type of continuous flow through hot water heater is often referred to as a “condensing” model. 

The advantage of how these gas water heaters work is that they provide even greater energy efficiency, however, the purchase price is a bit more than for the standard flow through hot water heater models.   

Even many non-condensing models are now 6 Star rated or better.

Controlling the Flow Through Hot Water Heater Temperature

remote control how a gas water heater works

As the flow rate and temperature of the incoming water can vary, the ECU modulates the amount of gas that goes to the burner, turning it up or down, as the gas flow through hot water heater works (instant gas geyser working). This modulation of the gas and burner intensity is what keeps the water at a set temperature. 

This functionality is based on input from a water temperature sensor on the exit side of the heat exchanger. 

Some continuous flow through hot water heaters have temperature controllers that allow the user to pick a temperature lower than the factory pre-set. 

Theses controllers can be located on the flow through hot water heater itself, wired to a remote location -- like a kitchen or bathroom -- or even wireless (see image). 

The ECU takes the input from the controller to further modulate the gas flow and burner intensity (instant gas geyser working), keeping the water at the user’s desired temperature.

Most flow through hot water heaters come with their maximum temperature pre-set in the factory.

This is a safety precaution to help prevent possible scalding. 50°C is typical for residential applications.

Flow Through Hot Water Heater Power Supply

water turbine helps a gas water heater work

To power the sparking igniter, in order to ignite the gas, most continuous flow through hot water heaters are connected to your home’s power supply. 

However, there are some flow through hot water heaters 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 flow through hot water heater that just use a simple battery.

The turbine and battery powered units have a distinct advantage over the connected models, inasmuch as they will operate (instant gas geyser working) even during a power outage. 

The disadvantage of the turbine powered type is that the entire unit is physically larger than a comparable plug-in model, as well as more expensive.

How Does a Gas Water Heater Work -  Gas Water Heater Operation

The gas water heater works (instant gas geyser working) when cold water flows through the hot water heater after a hot water tap is opened inside your home.  The gas water heater operation starts when the water flow is detected by a sensor that ignites the gas burner, to heat the water in the heat exchanger. 

During flow through hot water heater operation (instant gas geyser working), the water typically flow through the hot water heater in a serpentine pattern through the heat exchanger, absorbing as much heat as possible. The result is hot water flowing from your tap.

An electronic control unit modulates the gas burner to maintain a set water temperature.

This is the simple explanation of how does a gas water heater work.

Many Manufacturers & Models of Flow Through Hot Water Heater

Please note that there are many manufacturers and even more models of tankless continuous flow through hot water heater, including both LPG and natural gas. Therefore, there can be variations in features, functionality and operation (instant gas geyser working) from the general descriptions provided above. 

You should always consult the specific manufacturer’s information when making a purchase selection or other decision. 

You should also always consult your owner's manual for advice on safe operation and maintenance.

Instant Gas Hot Water Systems Prices - Instantaneous Hot Water Price

Instant (instantaneous) gas hot water systems prices are typically from around $700 to $1575*. The instantaneous hot water heater price difference depends on the flow rate which is, in turn, dependent on the number of showerheads and taps.

Gas hot water tank prices typically range in cost from around $830 for a 135L to $1475 for a 360L, for gas hot water tank prices (gas hot water systems prices).

Efficiency star ratings also influence the instant water heater price, with higher star ratings typically cost more in both types.

*Note that instant (instantaneous) gas hot water system prices (instant water heater price) are indicative only, as of July 2019

Hot Water System Sizing?

Don't Calculate by Number of People or Bathrooms

The sizing information available is very confusing because manufacturers, and others, are trying to provide a simplified answer to a complicated question. 

Some suggest that you calculate by the number of bathrooms in your home while others say to go by the number of people in your family. 

Also, in many cases, their recommendations are based on the worst case scenarios, assuming higher consumption than your actual water use.

Buying Too Large Wastes Money

The result is that many people end up buying a larger system than they actually need. 

This costs them extra money when they buy the hot water system and will increase the ongoing operating costs, in many instances.

Factors to Really Consider

Simultaneous use is one of the fundamental determining factors.  

The number of people in your home combined with how and when they use hot water is the key. 

  • Do they all take showers at the same general time of day? 

  • Do they take showers simultaneously in different bathrooms?

  • Do the showers have WELS 3 Star Rated Showerheads (maximum 9L/Min) or standard 18 to 25L/Min showerheads?

  • Do some prefer baths, which use more hot water? Is the bath or spa oversized, requiring even more hot water?

  • Do you run the washing machine, using hot or warm water, while people are showering?

  •  Is your dishwasher connected to the cold or hot water? If hot, do you use it while hot water is being used elsewhere?

Showers Are the Key - Water Saving Shower Head

Showers use the most hot water in a home.  People generally shower for 5 to 10 minutes. Assuming you have a 3 Star water saving shower head and you mix in some cold water with the hot, the typical hot water consumption would probably be in the 7 litres per minute range. 

If you also assume an 8 minute shower, water saving shower head will consume about 56 litres of hot water per shower or a family of four would consume 224 litres. 

The use of WELS (Water Efficiency Labelling and Standards) 3 star rated water saving shower head is an important factor in saving water and energy whilst reducing the size and cost of the hot water system required.

Hot Water Tank ExampleRinnai HOTFLO 170 gas hot water system

In the above example, if all four people take their showers in the morning, you would only need a storage hot water system with 224 litre first hour capacity, regardless of how many take showers at exactly the same time.  

This all presumes that you are not using any other hot water devices at the time.  

The use of additional hot water, after the shower period, would depend on the hot water system’s recovery time required to achieve full temperature.  

So, with a larger family or house guests, a bit of scheduling may be required to avoid the need for a larger unit.

Off Peak Electric Issues

Off peak electric storage units are a completely different story. 

Inasmuch as they only heat water at night, they need to be quite large to make sure you don’t run out of water during the day. 

So, some of the electric savings is offset by the fact that you need to heat a larger tank. 

The bigger tank would also cost more to purchase.

Tankless Flow Through Hot Water Heater Example

Bosch 21e tankless gas hot water systemFor a tankless continuous flow unit, it would depend on how many showers are being used simultaneously. 

Using the example above, if it’s two showers, then you only need a unit with a minimum flow rate of 14L/min. 

If you have 3 people showering at exactly the same time, you would need a minimum 21L/min.  

This does assume that you are not using other hot water devices simultaneously. 

Recovery time is not an issue with continuous flow units, so even a large family with guests would not run out of hot water.

Compare Gas Hot Water Heater Systems Prices

Now you can compare prices for all the major brands of gas hot water systems including Rinnai, Bosch, Kelvinator, Rheem, Dux and AquaMAX.

Click on your category of interest to compare prices:

Tankless Continuous Flow Gas Hot Water Systems Prices

Gas Storage Tank Hot Water Systems Prices

Gas Boosted Solar Hot Water Systems Prices

 

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The information in this article is derived from various sources and is believed to be correct at the time of publication. However, the information may not be error free and may not be applicable in all circumstances.