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7 Reasons to Choose Tankless Instant Hot Water System

We all try to save water but there are times when all you want is to enjoy a nice, warm, leisurely shower.

Why Choose a Tankless Instant Hot Water System?

  1. A Virtually Endless Supply of Hot Water

  2. They save energy and money

  3. Compact design saves space and looks better

  4. They have reduced emissions, as higher star ratings equate to lower CO2 output

  5. Longer lasting designs

  6. Cleaner and fresher water

  7. Healthier and safer designs inhibits bacteria growth

Instant Hot Water System

What are instant hot water systems?

Rinnai Infinity Gas Hot Water SystemsInstant gas hot water heater systems provide hot water on demand whenever you turn on the tap and you save energy, too.

These units only heat the water as it passes through.

Instant gas hot water systems are wall mounted and compact.

Optional temperature control of your gas hot water in different rooms.

Instantaneous Gas Hot Water Systems is another name for this type

  • Some call them instantaneous or continuous flow whilst still others just call them an instant hot water system

  • You'll never run out of hot water...even when extra guests drop in

  • You save money as these gas water heaters only heat the water you need

  • Optional controllers enable temperature control and auto bath fill

Instantaneous (Instant) Gas Hot Water Systems Prices

Instantaneous (Instant) gas hot water systems are typically priced from around $700 to $1500*.

The price difference depends on the flow rate which is, in turn, dependent on the number of showerheads and taps.

Storage tank style gas hot water heaters range in size from around 130L to 350L, with prices from approximately $800 to $1450*.

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

*Note that prices are indicative only, as of October 2018

Guilty Pleasures in Limited Supply

Let’s admit it... most of us like to indulge occasionally. 

Living in the country and depending on tank water, I do try to wait for a big storm when the rain water tank is overflowing in any case. 

Guilty pleasures

Makes me feel less guilty!

However, I’m not the only one in the family with that idea. 

My wife likes to run a full bath and others are ready to take advantage, too. 

We would have a problem if we were relying on a storage tank water heater, with a limited supply of hot water. 

The problem would be even worse if we had an off-peak electric water heater. 

Somebody would end up very disappointed.

The Solution

The good news is that there is a simple solution to the problem. 

Tankless instantaneous gas hot water systems provide a continuous flow of hot water.

In fact, there are seven reasons that you should consider going tankless:

1. A Virtually Endless Supply of Hot Water

Tankless hot water systemTraditional storage tank hot water heaters can only heat a certain number of litres at a time. 

Most residential hot water heaters are in the 135L to 170L range. 

Off-peak electric units need to be considerably bigger, because they have to last through the whole day. 

Once all of that pre-heated water in the tank is used up, it needs a recovery period to get the fresh contents back up to an acceptable temperature. 

If it runs out mid-shower your only choices are to finish with a cold shower or to stay soapy while you wait for the water to reheat. 

You’d be soapy for quite a while.

With a tankless hot water system, the water is heated as you need it and it can maintain the flow rate indefinitely. 

So, no running out of hot water no matter how many family members line up for the shower.

2. Save Energy

When you eliminate the large tank, you also save all of that energy being used to maintain the temperature of the stored water 24/7. 

In contrast, within tankless hot water systems the burner only needs to run when the hot water is actually needed.

3. Space Savings

Bosch 26e

Removing the bulky storage tank saves space. 

At about the size of a small suitcase, tankless water heaters are a fraction of the size of a traditional storage tank heater.  

The smaller tankless units are also more aesthetically pleasing, as it doesn’t dominate the exterior of your home.

4. Reduced Emissions

Greenhouse gas emissions are reduced through the use of tankless water heaters. 

Tankless hot water heaters come in LPG or natural gas models.

Tankless gas hot water systems produce about a third of the greenhouse gas emissions of electric storage hot water systems.

5. Longer Lasting

Traditional storage tank water heaters have a life span of around 10 to 12 years. 

Tankless hot water systems can last up to 20 years.

6. Cleaner & Fresher Water

Water from a storage tank water heater may pick up bits of rust and scale that build up within the tank. 

Since there's no tank to rust and no water stored with a tankless system, the water stays cleaner and fresher.

7. Healthier & Safer

With tankless systems, you only need to heat the water to 50°C, as the prevention of bacterial growth is NOT an issue with tankless units, as it is with all of the other alternatives that have tanks. 

So, less chance of scalding and no breeding ground for Legionnaires’ disease, or Legionellosis, that is caused by a bacterium, Legionella pneumophila. 

It is a respiratory disease that can cause severe pneumonia and is sometimes fatal.

How a Tankless Water Heater Works

Schematic of continuous flow hot water heaterIn summary:

• Cold water flows into the water heater when a hot water tap is opened inside your home.

• The water flow is detected by a sensor that ignites the gas burner, to heat the water in the heat exchanger.

• The water typically follows a serpentine pattern through the heat exchanger, absorbing as much heat as possible.

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

See all the details on:

How a Tankless Hot Water Heater Works

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

Instant gas hot water system problems...

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

Showers use the most hot water in a home.  People generally shower for 5 to 10 minutes. 

Assuming you have a 3 Star 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, you 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 showerheads 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.

Instantaneous Electric Hot Water System

Instantaneous electric hot water systems suffer from the peak electricity tariffs.

As they are used during the peak hours, with no storage tank, they do not take advantage of off peak rates.

So, virtually all of the use would be during the more expensive peak periods.

Tankless Hot Water 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.


For more information, click to see:

Hot Water Heater System Reviews


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:

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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.