Understanding the Functionality of Tankless Water Heaters

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On-Demand Heating Systems

For large households, more than one tankless unit may be required to fulfill their hot water needs.
©istockphoto.com/Justin Horrocks

Before delving into how tankless water heaters operate, it’s important to first comprehend the mechanism of standard tank heaters. Traditional heating systems consist of a large tank that houses and heats water. To provide hot water on demand, the tank constantly heats the water to maintain a consistent temperature. This process leads to standby heat loss, meaning energy is consumed to keep the water hot even when it’s not being used. For more information on tank heaters, refer to the article, How Water Heaters Work.

Tankless systems, also known as on-demand water heaters, avoid energy waste by only heating incoming water as it is required. This is the factor that makes tankless systems more efficient than traditional heaters. More details on this aspect will be covered later.

In order to provide you with hot water, tankless water heaters use a powerful heat exchanger to increase the temperature. A heat exchanger is an apparatus that transfers heat from one source to another. Other examples of heat exchangers are found in your air conditioner, refrigerator, and car radiator. In the case of a tankless water heater, it transfers heat produced by electric coils or a gas-fired burner to the water that comes out of your faucet. The exchanger is activated when water flows into it. When you turn on the hot water tap, the incoming water travels through the activated exchanger, which heats the cold water to your desired temperature. At this point, all you need is soap and shampoo to have a refreshing shower experience.

Tankless systems come in two variations, point-of-use heaters and whole-house heaters. Point-of-use systems are compact and heat water for a single or a couple of outlets, such as a kitchen sink. Due to their size, they can be installed beneath a cabinet or in a closet. They’re beneficial because they can be placed closer to the outlet and prevent water loss due to lag time. Lag time refers to the amount of time it takes for the hot water to reach your faucet. For large households, the lag time can be significant, taking several minutes. This implies that even though your water heating bill may decrease, your water consumption will increase, which is a factor to consider when deciding whether or not to switch to a tankless system. Whole-house systems are more expensive, larger, and can cater to more than one outlet simultaneously.

Tankless water heaters are available in electric, propane, or natural gas models. Point-of-use models are typically electric, while whole-house systems use either natural gas or propane. Which model and heating source to opt for depends on various factors. Further details on these factors will be covered in the next section, enabling you to make an informed decision when purchasing your tankless heater.


1. What is a tankless water heater?

A tankless water heater, also known as on-demand water heater, is a device that heats water as it passes through the unit, without the need for a storage tank. It uses a heat exchanger to instantly heat the water when you turn on the hot water tap.

2. How does a tankless water heater work?

When you turn on the hot water tap, cold water enters the unit and passes through a heat exchanger. The heat exchanger is activated by a flow sensor and a computer chip that controls the gas burner or electric heating elements. The water is heated instantly and delivered to your faucet or shower. Tankless water heaters can provide a continuous supply of hot water as long as there is demand for it.

3. What are the advantages of a tankless water heater?

One of the main advantages of a tankless water heater is that it provides hot water on demand, without the need for a storage tank that can take up valuable space in your home. It is also more energy-efficient than a traditional water heater, as it only heats water when it is needed, resulting in lower energy bills. In addition, tankless water heaters have a longer lifespan than traditional water heaters, as they are less prone to rust and corrosion.

4. Are there any disadvantages to a tankless water heater?

One potential disadvantage of a tankless water heater is that it may not be able to provide enough hot water for large households or during peak demand periods. If multiple hot water taps are being used simultaneously, the unit may struggle to keep up with the demand. Another disadvantage is that tankless water heaters may require more frequent maintenance than traditional water heaters, as mineral buildup can occur in the heat exchanger.

5. How do I choose the right size of tankless water heater?

The size of the tankless water heater you need will depend on your hot water usage and the number of people in your household. A professional plumber can assess your needs and recommend the appropriate size of unit for your home. It is important to choose a unit with a high enough flow rate to meet your hot water demands, but not so high that you end up oversizing the unit and wasting energy and money.

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