How Does A Tankless Water Heater Work? – Forbes Advisor

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A water heater is an increasingly popular alternative to conventional water heaters, such as storage heaters. While standard water heaters contain and store the water, instantaneous water heaters, as the name suggests, are able to produce hot water on demand without storing it beforehand.

How do instant water heaters work?

Instantaneous water heaters use electricity or gas to heat cold water almost immediately after entering the device. If the water heater is operated with gas, the water is heated with a gas burner, while it is operated with electricity, the water is heated with electrical resistance heating registers.

For water heater owners, this means essentially unlimited supply of hot water at around two to five gallons per minute.

Getting started with a water heater

If you are thinking of swapping out your traditional water heater for a water heater, consider the temperature of the groundwater in your residential area. If you live in the northernmost part of the United States, you can expect your average water supply to be between 35 and 40 degrees Fahrenheit. If you live in the southernmost part of the country, expect about 70 degrees Fahrenheit.

You should then calculate the difference between the coldest average groundwater temperature in your area and your ideal starting temperature for the water your water heater is supplying (in most cases you want this to be between 100 and 115 degrees Fahrenheit).

Then determine the required flow rate of your water heater, which is measured in gallons per minute. To calculate the amount of flow required for your home, add up the gallons per minute needed for each device that is powered by your water heater and that you may be using at the same time (e.g. you are going to take a shower). The result is the flow rate required for your home.

Additionally, you should consider the pros and cons of a water heater before investing in one.

Advantages of the instantaneous water heater


  • Instantaneous water heaters are much more compact than conventional water heaters and thus save space in your home.
  • Instantaneous water heaters can provide an almost endless supply of hot water in a matter of minutes, so you can easily do all the tasks that require hot water.
  • Most instant water heaters have a front-facing control panel that you can use to control their settings. If you have a gas-powered water heater, this means the ability to adjust the gas value, and with electric water heaters, it means controlling electricity consumption. Many users appreciate this feature as it allows them to manage their water, heat and electricity bills.


  • Instantaneous water heaters can reduce your energy costs in the long run compared to a traditional water heater.
  • A water heater lasts up to 20 years, which is longer than a conventional water heater. This means a reduction in the amount of waste that ends up in a landfill.

Disadvantages of the water heater

Risk of abuse

  • With an instantaneous water heater, you run the risk of incorrectly calculating your desired flow rate. Underestimating this number can cause serious inconvenience to your home. For example, if you have a dishwasher and a washing machine running at the same time and you have misjudged your daily hot water needs, it may mean that you and other household members are not allowed to have a hot shower.
  • Also, overloading the system can cause the system to shut down completely, which can result in the home not having hot water for hours (or longer).

Performance problems

  • Instantaneous water heaters may not function properly if their air supply is blocked and the heater cannot vent. In addition to endangering your hot water supply, this situation represents a serious fire hazard.
  • Sometimes a gas-fired instantaneous water heater does not ignite properly, usually because the gas supply to the heaters is low. While this problem can usually be resolved by closing all open gas valves, it can be uncomfortable for users.

Mineral build-up

  • While this isn’t unique to water heaters (it also happens with standard water heaters), mineral build-up can be a problem. Heat causes the calcium and magnesium in water to form a scaly substance that grows over time. If improperly handled, the deposit can affect the performance of tankless water.
  • To avoid problems with mineral deposits, owners of instant water heaters must regularly check their water supply and change the water filter regularly.


  • A water heater costs significantly more than a standard water heater, with a national average of around $ 2,200.
  • In most cases, you will need to have a plumber install your water heater, which can cost up to $ 450.
  • To compensate for the possibility of system overload, some homeowners (especially those with large houses) are given two or even three water heaters, which is too expensive for some.

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