Tankless Water Heaters Buying Guide

Tankless water heaters, (also called instantaneous or tankless water heater is used only when there is a demand for hot water.

How Does It Work?

Tankless water heaters heat water directly without the use of a storage tank. Therefore, they avoid the standby heat losses associated with storage water heaters. When a hot water tap is turned on, cold water travels through a pipe into the unit. In an gas tankless water heater, a gas burner heats the water. As a result, tankless water heaters deliver a constant supply of hot water. You don't need to wait for a storage tank to fill up!  Typically, tankless water heaters provide hot water at a rate of 2 to 5 gallons per minute, and opt for a heater that runs two applications at once. 

Common Applications

* Remote BBQ or outdoor sink. * Poolhouse or pool shower. * Remote bathrooms or hot tubs. * To serve as a booster, eliminating long pipe runs, for solar water heating systems, dishwashers, and sanitation. For homes that use 41 gallons or less of hot water daily, tankless water heaters can be 24% to 34% more energy efficient than conventional storage tank water heaters. They can be 8%  to 14% more energy efficient for homes that use a lot of hot water (roughly 86 gallons per day). You can achieve an even greater energy savings of 27%  to 50% if you install a tankless water heater at each hot water outlet.

Selecting a Tankless Water Heater

Fuel Types

The first thing that you'll need to decide when selecting a tankless water heater is the fuel type. You will need to select between an electric heater from companies such as Aquastar's.


Many retailers sell units that will accommodate 110V, 120V, 208V, 220V, 240V, and 277V.


Different electric tankless water heaters will have various requirements in amp draw. You will want to ensure that you can support the electrical demands of yours.

Circuit Breaker

* You must ensure that you have a circuit or circuits that will support your electric tankless water heater. It may be necessary to put yours on its own circuit or circuits. * You should consult with a qualified, licensed electrician for more information.

Venting Requirements

You will first need to identify whether your gas type is Category III stainless steel (UL1738 certified) venting. "Type B" venting accessories are not acceptable. Also, be sure to check local building code to ensure that your specific needs will be completely met. * Additionally, many tankless water heater manufacturers offer appropriate gas venting pieces.

Location, Size, and Demand

When deciding which tankless water heater to purchase, you will want to consider where you will need hot water. Are you looking for a unit that will heat one shower (single point application), an entire bathroom (multipoint application), or an entire house, apartment or condo (whole house application)? It is important to recognize the number of fixtures that will require hot water. Each fixture will have its own demands. The chart below illustrates the typical flow rates (demand) for some standard fixtures: The flow rate is especially important, since tankless water heaters will generate a temperature rise based on the flow rate demanded. For example, a Stiebel Eltron Tempra 12, running on 240 Volt power, will raise the water temperature by 54°F at 1.5 gpm, 36°F at 2.25 gpm, and 27°F at 3.0 gpm, above the ambient incoming water temperature, up to 125°F. A larger unit, like the Stiebel Eltron Tempra 36, running on 240 Volt power, will raise the water temperature by 92°F at 1.5 gpm, 92°F at 2.25 gpm, and 82°F at 3.0 gpm, above the ambient incoming water temperature, up to 125°F. This means that if you are using a 1.5 gpm shower and a 1.5 gpm kitchen sink simultaneously, a total demand of 3.0 gpm, the Stiebel Eltron Tempra 36 will raise the temperature 82°F. Next, you should look at your ambient incoming water temperature. If you live in a cold climate, like New York's, your incoming water temperature will likely be much lower than if you live in a warm climate, like Florida's. Your best bet is to find out how much temperature rise you will need in order for your hot water to reach the desired heat. If the ambient incoming water temperature for your shower is 65°F, you are using a 2.0 gpm shower, and you want to raise that temperature to 115°F, you will want to look for a tankless water heater that will provide at least a 50°F temperature rise at 2.0 gpm (115°F - 65°F = 50°F). However, if you anticipate additional simultaneous demand, such as the hot water from a sink being used while someone is showering, you will need to add the sinks gpm to the shower's gpm in order to determine your overall gpm demand and then find the temperature rise necessary to meet your overall needs.


You may have a specific application in mind for your tankless water heater. Here are a few examples of the different models and their functionality for a specific application:

Single Point Application

A single point application is one where only one fixture will require an electric tankless water heater. Here are some examples of single point electric tankless water heaters: * Eemax Single Point * Stiebel Eltron Single Point

Flow Controlled

The "Flow Controlled" range of water heaters from Eemax are ideally suited to serve two points, like two sinks, in close proximity. Here is an example of flow-controlled electric tankless water heaters: * Eemax Flow Controlled


The thermostatic tankless water heater serves as a booster for temperature loss from long pipe runs, dishwashers, and sanitation. Thermostatic units are good for applications where precise temperature control is essential, such as schools, hospitals and laboratories. Here are some examples of thermostatic electric tankless water heaters: * Eemax Thermostatic *

Whole House

Larger whole house units are designed to serve an entire house, apartment, condo, or cabin, where multiple points of use will exist. Here are some examples of whole house electric tankless water heaters: *
Eemax EX280T2T Series Three * Stiebel Eltron Tempra Series * Stiebel Eltron Tempra Series * Rheem Indoor

Whole House: Outdoor Use

Larger Whole House units are designed to serve an entire house, apartment, condo, or cabin, where multiple points of use will exist. Here are some examples of Whole House Electric Tankless Water Heaters for Outdoor use: * Rheem Outdoor

Installation and Maintenance

Proper installation and maintenance of your tankless water heater can optimize its energy efficiency. But it depends on many factors, which include climate and local building code requirements. You should have a qualified, licensed plumbing and heating contractor install your tankless water heater. Do the following when selecting a contractor: * Request cost estimates in writing. * Ask for references. * Check the company with your local Better Business Bureau. * Confirm the company will obtain a local permit, if necessary, and understands local building codes. Be sure you contractor first consults the manufacturer’s installation and instruction materials. Manufacturers usually provide the necessary installation and instruction manuals with the product. Your contractor should also contact your municipality for information about obtaining a permit, if necessary, and about local water heater installation codes. Periodic water heater maintenance can significantly extend your water heater's life and minimize loss of efficiency. Read your owner's manual for specific maintenance recommendations.

Popular Manufacturers

There are many manufacturers of tankless water heater, including those below: * CPO * Eemax * Stiebel * Bradford * Rheem

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