Home AppliancesWater Heater

What Is an On-Demand Water Heater?

Water Heater 6

An on-demand water heater, also known as a tankless, instantaneous, or demand-type water heater, is a device that instantly heats water as it flows through it. Unlike traditional water heaters with storage tanks, on-demand water heaters do not store hot water and therefore do not have standby heat loss, which is the energy wasted by heating water only to store it in a tank. These water heaters can be powered by gas or electricity and are available in various sizes and capacities.


An on-demand water heater, also known as a tankless or instantaneous water heater, is a device that heats water instantly as it flows through it. Unlike traditional water heaters, it doesn’t store hot water, but heats it directly when needed. This can lead to energy efficiency, lower utility bills, a continuous hot water supply, and space savings due to its compact size. However, it may have higher upfront costs and a limited flow rate compared to traditional tank water heaters.

How Does It Work?

On-demand water heaters work by directly heating water when it is needed. When a hot water tap is turned on, cold water flows into the heater. A flow sensor activates the heating element, which can be either gas jets or electric coils. The water then passes through a series of coils or pipes that are heated by the energy source, thereby heating the water. The heated water then exits the heater and travels through the pipes to the tap or appliance that requires hot water.

Intelligent electronic controls in tankless heaters allow for precise temperature control. The temperature is adjusted according to the rate of water flowing through the heat exchanger, and efficiency is optimized by modulating the amount of gas or electricity supplied to control the heat produced.

Advantages of On-Demand Water Heaters

On-demand water heaters offer several benefits:

  1. Energy efficiency: On-demand water heaters only heat water when it’s needed, making them more energy-efficient than traditional storage tank water heaters.
  2. Lower utility bills: Due to their energy efficiency, on-demand water heaters can lower your utility bills.
  3. Endless hot water supply: They provide hot water on demand, eliminating the issue of running out of hot water stored in a tank.
  4. Compact size: They are small and can be wall-mounted, saving valuable space in your home.
  5. Long lifespan: Tankless water heaters typically have a longer lifespan than traditional storage tank water heaters.

Disadvantages of On-Demand Water Heaters

Despite their advantages, on-demand water heaters come with their own set of challenges:

  1. Higher upfront costs: They are generally more expensive to buy and install than traditional tank water heaters.
  2. Limited flow rate: They can only heat a certain amount of water at a time, which may cause issues if multiple hot water applications are running simultaneously.
  3. Inconsistent water temperatures: Due to the on-demand heating process, water temperatures can vary depending on the flow rate and simultaneous hot water usage.

What to Consider When Purchasing an On-Demand Water Heater

When purchasing an on-demand water heater, consider the size, fuel type, energy efficiency, installation requirements, point-of-use vs. whole-house, special features, outdoor vs. indoor installation, warranty, and cost.


In conclusion, on-demand water heaters are an energy-efficient solution for hot water supply in homes. They offer numerous advantages such as energy savings, endless hot water supply, and compact size. However, they may have higher upfront costs and may require modifications to your home’s wiring, water lines, and gas lines. Therefore, it’s important to weigh the pros and cons before deciding if an on-demand water heater is the right choice for you.

Frequently Asked Questions

What is the average lifespan of an on-demand water heater?

The average lifespan of an on-demand water heater is around 20 years, which is significantly longer than the typical 10-15 years for conventional tank water heaters.

Do on-demand water heaters require regular maintenance?

Yes, on-demand water heaters require regular maintenance to ensure they operate efficiently. This includes descaling the heat exchanger and checking the system for leaks.

How quickly can an on-demand water heater heat water?

An on-demand water heater can heat water almost instantly. However, the exact time may vary depending on the size of the heater and the temperature of the incoming water.

Can an on-demand water heater be used in a large household?

Yes, but it’s important to choose a model with a high enough flow rate to meet the hot water demands of a large household. Multiple on-demand water heaters can also be installed for simultaneous usage in different parts of the house.

Is it possible to install an on-demand water heater by myself?

While it’s technically possible to install an on-demand water heater by yourself, it’s generally recommended to hire a professional. This is because the installation can involve complex tasks such as modifying gas lines and electrical wiring, which can be hazardous if not done correctly.

Leave a Comment

Your email address will not be published. Required fields are marked *