Answering FAQs About Electric Tankless Water Heater

water heater

Buyer’s Guide

How to choose the right electric tankless water heater?

The water heater’s power is measured in kilowatts (kW), which usually refers to the power of the electric heating tube in the water heater. The greater the power, the more heat that can be generated.  This means less heating time is required and there is a higher load on the wire.

The power of common water heaters on the market are 6.5kW, 9kW, 14kW, 18kW, 27kW, etc.

When purchasing an electric tankless water heater, you can choose your preferred power level for what you need, the number of faucets, and the water consumption habits.

Normally, the climate in the southern US is warmer and the requirements for the heat load (power) of the water heater are lower. From an economic point of view, 14kW water heaters can meet the requirements of comfortable bathing. In the northern US, the water temperature is lower, especially in winter when the heat load (power) of the water heater is required to be large enough to meet the requirements of comfortable bathing, so families farther north should choose an 18kW water heater.

If you have multiple showers, choose a high-power capacity water heater or try to install multiple water heaters.

If you have a large house, install an on-demand water heater at each hot water outlet, which will provide more constant hot water while achieving energy savings of 27%–50%.

Whether the water heater can be used or not depends mainly on the local inlet water temperature and water flow -- usually measured in gallons per minute (GPM).


Average GPM Usage for Common Appliances




Low Flow Faucet



Bathroom Faucet



Kitchen Faucet






*The flow rate for each symbol is represented in the GPM (gallons-per-minute) column of the table above. The Range column indicates variations in GPM for faucets and showers based on manufacturer and style.

Temperature Map

First, determine your average inlet water temperature by finding your location on the map and noting the color.

For example, the average inlet water temperature in Colorado is 47°F while the average inlet water temperature in most of Louisiana is 67°F.


Next, determine how many applications your tankless water heater can run simultaneously by matching your color to the table below.


KW Inlet Temp(°F) GPM Approx Usage Outlet Temperature(°F)
6.5 41 0.7  Low Flow Faucet 104
50 0.8  Low Flow Faucet
59 0.9  Low Flow Faucet
68 1.2  Bathroom Faucet
77 1.5  Kitchen Faucet
8 41 0.7  Low Flow Faucet 108
50 0.9  Low Flow Faucet
59 1.0  Bathroom Faucet
68 1.3  Bathroom Faucet
77 1.6  Kitchen Faucet
9 41 0.9  Low Flow Faucet 108
50 1.0  Bathroom Faucet
59 1.2  Bathroom Faucet
68 1.5  Kitchen Faucet
77 2.0  Shower
14 41 1.4  Kitchen Faucet 108
50 1.6  Kitchen Faucet
59 1.9  Kitchen Faucet
68 2.3  Shower
77 2.4  Shower
18 41 1.7  Kitchen Faucet 108
50 2.0  Shower
59 2.4  Shower
68 2.9  Shower
77 3.8  Shower
27 41 2.5  Shower 108
50 2.9  Shower
59 3.5  Shower
68 4.3  Shower
77 5.5  Shower

For example 1, suppose I am in California and I need a water heater for a bathroom. The inlet water temperature in my area is 72°F so I need to buy a 14kW water heater to meet my needs.

For example 2, suppose I am in California, and I have two bathrooms. Usually, my friend and I have a shower at the same time, so I need to buy two 14kW water heaters, one for each bathroom.

Will one tankless water heater be enough to heat my entire house?

Maybe. You must choose the proper model to suit your home’s hot water needs, which is based upon the maximum flow of hot water you need at any one time. You can buy tankless water heaters that are capable of handling one shower at a time and others that can sustain a maximum of two showers operating at the same time.

What If I live in a cold climate in the winter? 

The inlet water temperature varies from season to season, so it is advisable to choose a more powerful water heater to meet the hot water demand in winter. Smaller machines may be sufficient in the summer, but may encounter conditions that are not hot enough in the winter.

Feel free to contact us via if you have any questions on selecting the size of the tankless water heater. We'll be able to provide recommendations of the size of tankless for your unique climate.

Can this be installed on an exterior wall of my house?

The models need to be installed indoors. If you are referring to one of the foundation walls yes it can be installed but please be aware of any freezing in your area, you may have to have a layer of insulation between the wall and unit to prevent any damage by freezing temperatures. The benefit of tankless electric water heaters is that there is no venting required and can be mounted in most places of the home that are easily accessed for maintenance. If you have any further questions you can call our technical support line at 1-725-333-0437.

What is the power consumption of Airthereal electric tankless water heater?

The instantaneous power consumption while the hot water is running is quite high (up to 9kW, 14kW, or 18kW depending on which model you’re looking at on the product page). However, when no hot water is being used, the power consumption is 0 (or a minuscule amount to run an LED light or something). The total power consumption over the course of several days or longer should be much lower than a tank heater but the short-term power usage while the heater is making hot water will be much higher than a tank heater. It’s just that the unit sits idle most of the time while a tank heater will use power fairly frequently even when no hot water is needed as the water in the tank cools off over time and needs to be re-heated fairly constantly.

Is hot water from the water heater safe to drink?

Please DO NOT directly drink the water from the water heater. The water from the faucets must have drinking water quality and untreated plumbing might have a bacteria risk, thus it is advised to not use heated water for drinking.

Does it work well with hard water?

Yeah, it’ll work great until it doesn’t. Hard water doesn’t affect the ability to heat the water. Over time, anythingattached to hard water can become damagedby hard water. You will need to flush the unit after 6 months to remove any mineralr calcium deposits. If minor then flush out once a year.



Why is the hot water not constant?

There are some affecting factors, which are water flow, the inlet water temperature, and the set temperature. Generally speaking, the power of the water heater may not fully satisfy the environment of your home. Maybe the inlet water temperature is too cold, or if you set a much higher temperature or the water flow in your home is quite large, the water heater is not strong enough to provide enough constant hot water.

What to do if there is no hot water?

If there is no hot water coming from your electric tankless water heater, please check the following points:

  1. Check if the machine is correctly installed and powered on: 
    1. Connected to the power supply, there is no beep sound or display, you may have a faulty breaker or unit may be wired incorrectly. Make sure the breakers at main electrical panel are ON;
    2. Check the wiring, the indicator L1 is connected to the neutral wire, L2 is connected to the live wire, and the other symbol indicates the ground wire. See the pic below:
  2. After powering on, check if the buttons respond well.
  3. Check if there is an error code on the screen. If so, follow the user manual instructions to eliminate it.


Failure Analysis



Leakage of electricity.

Contact Airthereal support for assistance.


Temperature exceeds 149°F/ 65°C.

A. Select a lower power level or turn down the temperature.

B. Increase water flow.


Water inlet temperature sensor failure

Contact Airthereal support for assistance.


Water outlet temperature sensor failure

Contact Airthereal support for assistance.


Water flow sensor got stuck.

Contact Airthereal for assistance.


4. System overloading: If there is no hot water but cold water, probably it's because too many faucets are being run at once. To overcome this problem, try to use one hot water appliance or install more tankless water heaters to meet your needs.


What yearly maintenance is required on this unit?

The estimated lifespan of Airthereal electric tankless water heaters is 5-8 years (depending on the daily usage).

Note: Do not attempt to repair this water heater yourself if the unit is not working properly.

Call a technician for assistance. The power supply always needs to be shut off before these operations are carried out.

To ensure consistent Maximum performance of the unit, it is recommended to follow these instructions:

  1. Periodically remove scale and dirt that may build up at the aerator of the faucet or in the shower head.
  2. There is a built-in filter at the inlet connection which should be cleaned from time to time. Please cut the water supply before cleaning this filter. You can then reverse the inlet and outlet pipe connection (connect each pipe to the opposite connection) and open the faucet to manually flush the filter by opening the faucet to its max. After flushing the filter in this way, remember to reverse the pipes back to the normal connections.
  3. If the water heater is not used for a long time (more than 3 months), please clean the water inlet waterway first in the state of power off (Not using it for a long time will cause oxidation of the water pipe, and dirty water will flow out), air and impurities must be removed before use.

Important Note

  1. Any maintenance performed on the water heater unit may introduce air into pipes. It is important to purge all the air out before powering on again. Failure to do so could cause serious damage to the heating element.
  2. If you have a water supply with high levels of mineralization (hard water), you should increase the frequency of your maintenance. Check the descaler device regularly to see if it is functional.
  3. Do not use paint thinner, alcohol, petrol, or any other chemical solutions to clean the unit. Use only a damp cloth with mild detergent to wipe away any dirt or debris.


If you don’t see the tankless water heater problem you’re having here, or if you need technical support with your water heater, please call us at 1-725-333-0437 or email us at

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