How does a tankless water heater work

Want to find out how does a tankless water heater work? We have written this article to help you understand what goes on inside a tankless water heater.

You’ll find the right tankless water heater for your household by knowing how a tankless heating system operates and its limitations.

One crucial error that homeowners make when purchasing a tankless device is to correctly scale the unit according to their home’s hot water requirements.

The concept behind a tankless water heater is that instead of continually heating the water contained in a tank, it heats the water when you need to.

Tankless water heaters have been the standard for quite some time in most of Europe and Japan, but they have not gained prominence in the United States until recently.

Read this article to learn how does a tankless water heater work.

How does a tankless water heater work

water heater

Without having a storage tank, tankless water heaters heat water directly. Coldwater flows through a pipe into the machine when a hot water tap is switched on. An electric heater or a gas burner supplies heat to the water.

Thus, tankless water heaters have a continuous supply of hot water—no need to wait for a storage tank with enough hot water to fill up. A tankless water heater’s performance, however, restricts the flow rate.

It’s essential to know how a regular tank heater functions to understand how a tankless water heater work. There’s a large tank in a traditional heating system that holds and heats the water.

The tank continuously heats the water to maintain a steady temperature to give you hot water when you need it.

Due to this feature, tankless heating systems prevent standby heat loss by incoming hot water just when you need it — they are also known as “on-call” water heaters.

What makes a tankless device more effective is removing the standby heat loss, but a little later, we’ll get to that in more detail.

What are the types of tank less water heater?

water heater

Two basic types of tankless water heaters are available – small units are typically mounted right at or near the point of use and larger units that can serve an entire building.

In addition to reducing standby losses from a tank, the smaller models can minimize or eliminate heat losses by piping. Still, multiple units are typically required to serve an entire building.

The smaller ones are useful because, due to lag time, they can be mounted closer to your outlet and reduce water loss. Lag time – the amount of time it takes to hit your faucet for the hot water.

The lag time can be necessary for large buildings, often as long as several minutes.

This means that while your energy consumption bill will go down, the use of water will go up, which is something you should consider when discussing whether or not to go tankless.

Whole-house systems are more significant, more costly, and more than one outlet can work at a time.

Larger, ‘whole house’ tankless water heaters provide hot water for several point-of-use at home. These units eliminates loss of heat from the tank though some heat loss still occurs through hot water piping if it is not insulated.

Fuel Types used in tankless water heater

water heater

You can choose from the battery, propane, or natural gas versions using tankless water heaters. Point-of-use models usually are electric, whereas whole-house systems typically are powered by natural gas or propane.

Usually, electricity or natural gas powers up tankless water heaters. Solar power, geothermal energy, crude oil and propane are also other options. Consumers may choose any fuel types based on availability and prices.

Since they can provide more hot water faster than other types, gas tankless water heaters are usually favored for more extraordinary demanding situations.

Gas is preferred in most parts of the world as it is more readily available and more accessible. However, gas can be a pain to mount, as it may be difficult and costly to achieve the necessary venting.

Electric water heaters without tanks are also efficient, especially where the water demand is average or lower. They usually level off at about 8 GPM, which is generally appropriate for a smaller family but much lower than a gas tankless heater’s capabilities.

Tankless electric water heaters use 30 to 50 percent less energy than traditional tank systems, saving around $100 or more per annum for a typical family, depending on water usage.

Usually, electric tankless water heaters are about 98% or more efficient, whereas tankless water heaters that uses gas are about 80-85% efficient.

According to Energy Star, conversion from a tank-style water heater to a tankless water heater would save a household of four members an average of $100 per year or over $1500 during the system’s lifetime.

Flow rate capability in tankless water heaters

water heater

The next choice homeowners need to consider is the flow rate capability. The flow rate, expressed in Gallons Per Minute (GPM), defines how much water can flow through the heater at any given time and be sufficiently heated.

This calculation, taken literally, tells us how many gallons of water the equipment will heat each minute, then push it to your appliances.

In regions with lower groundwater temperature, water heaters would have to work harder to keep up with the house’s water consumption while reaching the temperature needed.

The GPM calculation is then combined with another measurement called “temperature increase.”

To meet the bathroom sink and shower’s hot water requirements, the flow rate for your prospective tank will need to be at or above 3.2 GPM.

Tankless water heater Vs Tank style water heater

water heater

Key Differences

Tank less water heater
  • Heats water on-demand when a need occurs. As it moves through the appliance, the water is heated.
  • Big but one time investment.
  • Installation requires modifications.
  • Eco-friendly.
  • Design is compact.
  • Suitable size is crucial.
  • Can easily exceed 20 year lifecycle if maintained properly.
Tank style water heater
  • Stores water in the tanker after heating.
  • Economic prices in both purchasing and installation.
  • Frequently leakes and requires repairment.
  • Requires a lot of floor space.
  • Storage capacity ranges between 20 to 80 gallons.
  • Expected life cycle is typically 8 to 12 years.

Maintaining your tankless water heater

water heater

When you know how does a tankless water heater work, its vital to know a thing or two about its maintenance.

Buying a tankless water heater is a perfect way to reduce the associated cost of electricity and benefit from a constant supply of hot water on demand.

However, for you and your mates, as great as a tankless water heater can be, you don’t want to forget the value of preventive maintenance.

All mechanical devices and equipment need to be maintained periodically for maximum longevity and performance, and a tankless water heater is no different.

Knowing why it is essential and what needs to be done will help you prepare for this process.

Some common issues with tankless water heater

water heater

You can help prevent downtime related to maintenance problems by maintaining your tankless water heater. Over months and years, it can also theoretically help increase your system’s lifespan and improve energy efficiency.

Hard water is one of the most critical factors that can result in repairs, but routine system maintenance measures can minimize hard water related issues.

Hard water is full of minerals, and within your appliance, these minerals will result in scaling and other problems.

Although water hardness depends on the location, these same repair and maintenance problems can be faced even by homeowners elsewhere.

Any tap water flowing into your system, after all, has at least trace elements of minerals that can build up over time.

To deal with maintenance, you can schedule service or take a ‘DIY’ approach. The primary form of maintenance for most of these units requires cleaning the system in various ways.

If minerals have caked on the components in the unit, it is essential to make descaling attempts. It’s a smart investment to add an inline filter to minimize buildup significantly.

It is essential to take descaling attempts if minerals have caked up in the components.

Otherwise, general cleaning would be useful. These measures allow the device to run at peak efficiency and reduce energy costs associated with it.

Furthermore, these measures can decrease excessive wear and tear and may potentially help your appliance last longer.

Maintenance process of tankless water heaters


Descaling is expected from time to time if you live in an area with hard water. Descaling is the process involving the removal of the accumulated gunk within your system.

The minerals in the water will settle into your system and make a thick mess over time.

The method of descaling is similar to flushing, but it also requires running a large amount of water-vinegar through the tank. Within your machine, vinegar will break down the mineralized gunk.

You need to rinse or flush after using vinegar for demineralization process for upto 45 minutes. This way the all the matter including vinegar will be removed.


How does a tankless water heater work

Your  should flush your tankless water heater at least once a year to ensure it’s longevity. Depending on the hardness of your water, if it is low quality, you will find it safer to flush it two to three times each year.

Using a sediment trap or softener may also help with the hard water to a degree. Always be sure to check the manual supplied by your manufacturer to follow the specific instruction for your particular water heating system.


Now that you know how does a tankless water heater works, you will find it a lot easier to choose a perfect water heater for your home or office.

A proper routine maintenance will inevitably extend the longevity and proper utilization of your heating system.


Leave a Comment