Tankless Water Heaters Buying Guide
Tankless water heaters, (also called instantaneous or demand water heaters), provide hot water only as it is needed. Traditional storage water heaters produce standby heated water, and the energy used to do so costs you money. We don't heat our homes while vacationing; we heat them when it is needed. Similarly, a tankless water heater
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 electric tankless water heater
Typically, tankless water heaters provide hot water at a rate of 2 to 5 gallons per minute. Typically, gas-fired tankless water heaters will produce higher flow rates than electric ones. Some smaller models, however, cannot supply enough hot water for simultaneous, multiple uses in large households. For example, taking a shower and running the dishwasher at the same time can stretch a tankless water heater to its limit. To overcome this problem, you can install multiple heaters, connected in parallel for simultaneous demands of hot water. You can also install separate water heaters for specific appliances that use a lot of hot water in your home.
Common Applications in the Home:
- 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
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The EcoSense by Rheem ECO-180XN Natural gas "On Demand" Tankless Water Heater
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Fuel Type
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 (like Eemax Tankless Water Heaters
Voltage
Many retailers sell units that will accommodate 110V, 120V, 208V, 220V, 240V, and 277V.
Amperage
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 natural gas
Next, you will need to consider venting requirements for your specific installation scenario. There are a few important things to keep in mind when purchasing the gas venting accessories
- Be sure that you purchase 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 gas venting "kits". It is recommended that customers evaluate the needs of their specific installation to ensure that they will be getting all of the necessary gas venting accessories. Depending on where you will be installing the tankless water heater, a pre-made kit will probably not meet your needs. Ensure that you measure out the vent route and consider where the discharge will go, consider the necessary clearances, and consider ample access to air for combustion; then buy the 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 the water at one bathroom sink (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:
Typical Flow Rates in Gallons per Minute (gpm) | |||||||
| Fixture Type | Lavatory | Bathtub | Shower | Kitchen Sink | Pantry Sink | Laundry Sink | Dish-washer |
| Flow Rates | 0.5 | 2.0 – 4.0 | 1.5 – 3.0 | 1.0 – 1.5 | 1.5 – 2.5 | 2.5 – 3.0 | 1.0 – 3.0 |
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
A larger unit, like the Stiebel Eltron Tempra 36
| Temperature Rise Based on Flow Rate, Up to 125°F | |||
| Flow Rate | 1.5 gpm | 2.25 gpm | 3.0 gpm |
| Tempra 12 | 54°F | 36°F | 27°F |
| Tempra 36 | 92°F | 92°F | 82°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 12
Next, you should look at your ambient incoming water temperature. If you live in a cold climate, like New York, your incoming water temperature will likely be much lower than if you live in a warm climate, like Florida. 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.
 60° F Incoming Water |  |  2 gpm Shower | |  110° F Desired Output Water Temperature |  |  You will need a tankless water heater that produces a 50°F temperature rise at 2 gpm. |
Application
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:
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:
Thermostatic
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:
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:
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:
Installation and Maintenance
Proper installation and maintenance of your tankless water heater can optimize its energy efficiency.
Proper installation depends on many factors. These factors 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:
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