Tankless water heaters have become increasingly popular due to their energy efficiency and convenience. Unlike traditional storage tank water heaters, tankless water heaters heat water on-demand, which means they only use energy when hot water is needed. If you’re considering switching to a tankless water heater, you may be wondering how much energy it uses. In this article, we’ll explore the energy usage of tankless water heaters and provide you with all the information you need to make an informed decision.
What is a Tankless Water Heater?
A tankless water heater, also known as an on-demand water heater, is a system that heats water as it passes through a heat exchanger. When a hot water tap is turned on, cold water flows through the unit and is heated by the heat exchanger, providing instant hot water. Tankless water heaters can be powered by electricity, natural gas, or propane.
Energy Efficiency of Tankless Water Heaters
One of the main advantages of tankless water heaters is their energy efficiency. Traditional storage tank water heaters store and heat water continuously, which means they are using energy even when hot water is not needed. In contrast, tankless water heaters only heat water on-demand, which can result in significant energy savings.
According to the U.S. Department of Energy, tankless water heaters can be up to 34% more energy-efficient than storage tank water heaters for households that use less than 41 gallons of hot water per day. For households that use more than 86 gallons of hot water per day, tankless water heaters can be up to 14% more energy-efficient. Additionally, tankless water heaters have a longer lifespan than storage tank water heaters, which means they can provide even more energy savings over time.
Energy Usage of Electric Tankless Water Heaters
Electric tankless water heaters use electricity to heat water on-demand. The amount of energy used by an electric tankless water heater depends on the flow rate of the water and the temperature rise required. The flow rate refers to the amount of water that is passing through the unit, while the temperature rise refers to the difference between the incoming water temperature and the desired hot water temperature.
According to the U.S. Department of Energy, electric tankless water heaters typically use between 10,000 and 15,000 watts of power. This means that if you are using the unit at its maximum flow rate, you can expect it to use between 240 and 360 kilowatt-hours per month.
Energy Usage of Gas Tankless Water Heaters
Gas tankless water heaters use either natural gas or propane to heat water on-demand. The amount of energy used by a gas tankless water heater depends on the flow rate of the water, the temperature rise required, and the type of gas being used.
According to the U.S. Department of Energy, gas tankless water heaters typically use between 19,500 and 199,000 BTUs (British Thermal Units) per hour. This means that if you are using the unit at its maximum flow rate, you can expect it to use between 4 and 40 therms per month. One therm is equivalent to 100,000 BTUs.
Factors That Affect Energy Usage
There are several factors that can affect the energy usage of a tankless water heater, including:
Flow rate:
The higher the flow rate, the more energy the unit will use to heat the water.
Temperature rise:
The greater the temperature rise required, the more energy the unit will use to heat the water.
Climate:
In colder climates, the unit will need to work harder to heat the water, which can result in higher energy usage.
Frequency of use:
The more frequently the unit is used, the more energy it will consume.
Type of fuel:
The type of fuel used by the tankless water heater can also affect its energy usage. Natural gas and propane are generally more energy-efficient than electricity, but they may not be available in all areas.
Size of unit:
The size of the tankless water heater can also affect its energy usage. If the unit is too small for the household’s hot water needs, it may have to work harder to keep up with demand, resulting in higher energy usage.
Maintenance:
Regular maintenance of the tankless water heater can help ensure that it is running efficiently and not using more energy than necessary.
How to Calculate Energy Usage
To calculate the energy usage of a tankless water heater, you will need to know the unit’s flow rate and the temperature rise required. You can then use the following formulas:
For electric tankless water heaters:
Energy usage (in kilowatt-hours) = (watts x hours used) / 1000
For gas tankless water heaters:
Energy usage (in therms) = BTUs per hour x hours used / 100,000
Keep in mind that these formulas only provide an estimate of the energy usage, as there are other factors that can affect energy consumption, such as the climate and frequency of use.
Conclusion
Tankless water heaters are an energy-efficient and convenient way to provide hot water on-demand. The amount of energy they use depends on several factors, including the flow rate, temperature rise, type of fuel, and size of the unit. Generally, electric tankless water heaters use between 10,000 and 15,000 watts of power, while gas tankless water heaters use between 19,500 and 199,000 BTUs per hour. By understanding the factors that affect energy usage and performing regular maintenance, you can help ensure that your tankless water heater is running efficiently and not using more energy than necessary.
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