Rheem Tankless Water Heaters Buyer's Guide

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What is a tankless water heater?

A tankless water heater is a water heater that heats water without the use of a storage tank. Because a tankless water heater creates hot water only when needed, tankless water heaters do not experience the standby heat losses associated with tank-based water heaters and are able to provide an endless supply of hot water.

Rheem RTG-95DVLP Tankless Water Heater

How do tankless water heaters work?

Activated by Cold Water From Your Hot Water Tap

When your hot water tap is opened, cold water enters the water heater and triggers the heating elements or burners.

Cold Water Becomes Hot in Just Seconds

The cold water passes through the heat exchanger, which has become very hot due to its placement directly above the heating elements or burners. Heat is transferred from the heat exchanger, usually made of solid copper, to the water. As you change the water flow, a water valve or thermostat controls the heating elements or burner flame to maintain a constant water temperature. The amount of energy used is always proportional to the volume of hot water being used.

Shuts Down When Your Hot Water Tap is Turned Off

When the hot water tap is turned off, the heating system also turns off.

Why go tankless?

In short, tankless water heaters provide endless hot water, save you money almost immediately and stay effective for a long time.

Here is a list of reasons why more and more people are choosing to go tankless:

Endless supply of hot water – Tankless water heaters heat water instantly, so you'll never run out of hot water as you might with a tank-based water heater.

Energy-saving – Tankless water heaters only consume energy when you're using hot water instead of continuously, as tank-based water heaters do. This energy efficiency can save you up to 56% on water heating energy costs.

Government Tax Credits – Buyers of tankless water heaters with Energy Factors (EF) of at least 0.80 can qualify for federal tax credits.
Space-saving – Tankless water heaters are typically much smaller than tank-based water heaters, because they don't need to hold 40+ gallons of water in them. Most tankless water heaters can be hung on a wall.

Built To Last – Tankless water heaters are built to last 20 or more years versus just two to nine years for tank-based water heaters.

Maintains efficiency longer – A tankless water heater maintains its efficiency throughout the lifetime of the unit. Storage tank water heaters decrease in efficiency over time due to mineral build-up inside the tank. This is due to the fact that storage tank water heaters store hot water, giving minerals a chance to settle and bake from the heat onto the walls of the tank and onto the heating element in electric models, thereby reducing heat transfer.

Environmentally-friendly – Unlike traditional tank-based water heaters, tankless water heaters are almost completely recyclable and do not have to go to a land fill when their time is up.

Non-corrosive – A tankless water heater will not develop a corrosive leak like a storage tank water heater might, saving you from expensive water damage in your home.

Note: A tankless water heater can leak if it is exposed to freezing temperatures or has a manufacturing defect.

How do I select a tankless water heater?

In selecting the right tankless water heater for your needs, you should focus primarily on three things:

1) Flow Rate
2) Fuel Source
3) Gas-Specific or Electric-Specific Requirements

Flow Rate

How many hot water applications do you need to support?

If you plan on supporting two or more major hot water applications simultaneously (e.g.: showers/baths, washing laundry w/ hot water), you'll be primarily focused on choosing a gas tankless water heater, as gas tankless water heaters are able to heat a greater volume of water than electric water heaters.

If you only intend on supporting one major hot water application (such as a shower or washing machine) or up to two minor applications (such as a sink), you can consider either a gas-powered or an electric water heater.

Depending on your application needs, you'll need to find a tankless water heater with an appropriate flow rate. (i.e.: the volume of hot water the water heater is able to produce, typically measured in gallons / minute or GPM)

Here are estimated flow rate requirements for common hot water applications:

Note: If you live in a cold climate, you'll need a water heater that supports higher flow rates than those listed above. Call CPO Rheem at 1-800-714-9833 if you need assistance determining your flow rate requirements.

Fuel Source

Gas or Electric?

Go gas for greater flow rates and superior energy efficiency

If you're looking to purchase a tankless water heater to provide hot water to an entire home or business, we strongly recommend that you go with a gas-powered unit, as they typically provide greater flow rates and are more energy efficient than electric units. For instance, if you'd like to be able to support two showers at the same time, you're best served going with a gas tankless water heater.

Be prepared to invest a little more time planning and installing if you're going to get a gas tankless water heater, however, because you'll have to consider venting, clearances, gas sizing and combustion air requirements before you're able to choose a specific water heater.

Learn more about Gas-Specific Requirements

Go electric for ease of installation and light / moderate usage requirements

Electric units are generally best in smaller environments such as a guest home or small apartment, or where it may be difficult to meet the venting, clearances, gas sizing and combustion air requirements associated with gas tankless water heaters. Some people opt for an electric tankless water heater because they don't have access to natural gas and don't want to deal with propane containers. Generally, electric tankless water heaters are much easier to install than gas tankless water heaters, because the only significant requirement to meet is having the correct amperage. Keep in mind, however, that most electric tankless water heaters only support one major application (such as a shower) at a time.

Learn more about Electric-Specific Requirements

Natural Gas or Liquid Propane?

If you've decided to go with a gas tankless water heater, your next step is to determine if you'll be using natural gas or propane gas (also known as liquid propane). Generally, tankless water heater manufacturers offer comparable natural gas and liquid propane versions of each water heater model.

The information below may help you determine your gas type:

-propane is delivered by truck or purchased at stores while natural gas is piped into buildings from gas lines.

-natural gas is measured and billed to you in "cost / therm", while propane is measured and billed in "cost / gallon".

Gas-Specific Requirements

Gas Sizing

If you're interested in purchasing a gas tankless water heater, you'll need to make sure your gas line, the pipe through which gas travels when it has reached your house, is compatible with the gas tankless water heater you're interested in. You'll need to ensure that both the diameter of the pipe and the distance of its run are compatible with the product you're considering.

IMPORTANT - Take a look at the installation manual of the specific product you're interested in for more information about its gas sizing requirements. Call your gas company or professional installer if you need help determining the proper sizing.

Combustion Air

Gas tankless water heaters require combustion air. If you're looking at buying an indoor gas tankless water heater, you'll need to consider how combustion air will be delivered to your water heater and how much combustion air is needed. Outdoor gas tankless water heaters usually get more than enough combustion air because they're installed outside, where combustion air is abundant.
How do I calculate if I have enough combustible air?

Multiply the Length by the Width by the Height of the room you're installing your tankless water heater in and add up the total BTUs that will be used (include the furnace if present, etc)
Single-Pipe Systems

If the indoor water heater you're considering does not have a second air pipe to draw combustion air from outside your home, you'll need to use the air within your home as combustion air. The amount of combustion air required (measured in cubic feet) will depend on how powerful your gas tankless water heater is. If you plan to install the gas tankless water heater in a confined area, such as a closet, you will likely need air ducts or additional air inlets.

Whenever possible, you should obtain combustion air from outside the home* - it is cleaner and will keep your gas tankless water heater operating at peak performance.

IMPORTANT - Check the installation manual of the specific product you're interested in for more information about its combustion air requirements.

*Some indoor tankless water heaters such as Rheem's RTGH-95DVLP use a two-pipe system, also known as a direct vent system, to obtain combustion air from outside through a second pipe.


Gas tankless water heater placement is another important factor to consider. Each gas tankless water heater will have different distance requirements between the heater and other parts of your home, as seen in the example above. Some of the clearances you'll need to consider are:

- Operable windows, doors and other fresh air openings
- Adjacent walls or tall bushes (ourdoor water heaters)
- Below gutters, sanitary pipework, eaves or overhangs (ourdoor water heaters)
- Distance above the ground
- From a gas meter, gas regulator, electrical box or another heater

IMPORTANT - Check the installation manual of the specific product you're interested in for more information about clearance requirements.


Gas tankless water heaters require gas exhaust venting to the outside. Some vent horizontally (through a wall), others vent vertically (through a roof or chimney). In most cases, water heaters and venting kits are sold separately.

IMPORTANT - Check the installation manual of the specific product you're interested in for more information about venting options.

Electric-Specific Requirements

If you're looking for an electric tankless water heater, the size of your breaker box and how many amps you have available are the most important factors to consider.

Depending on which electric tankless water heater best fits your home needs, the required amperage will be 150 or 200 amps.

IMPORTANT - Check the installation manual of the specific product you're interested in for more information on amperage requirements.

What are my installation options?

Because a water heater installation requires work to be done with water pipes, (and in many cases, gas lines) it is highly recommended that you hire a plumber to do the job.

Make sure the plumber you're considering has experience installing tankless water heaters, though. Although more and more plumbers are becoming knowledgeable about tankless water heaters, many still exclusively perform tank-based water heater installations.

How much can I expect to save on my monthly bill if I install a tankless water heater?

Test results have shown that a tankless gas water heater costs about 40% less to operate than an electric water heater, and about 30% less than a natural gas water heater.

Rheem tankless gas water heaters are more energy efficient than conventional water heaters, because they eliminate the need to maintain a large supply of heated water. A Rheem tankless water heater operates only when hot water is needed. Regardless of whether you currently have a conventional electric or gas water heater, the Rheem tankless will save money on your energy bills.

The Energy Factor, EF, of all Rheem tankless water heaters is over .81. By comparison, a standard tank type water heater has an EF of around .62, so you can see that they are inherently more efficient than a storage type water heater. A higher EF is only one of many reasons why tankless water heaters cost less to operate. A Rheem tankless water heater has no standing pilot light, no stand by loss, and the burners modulate to maintain maximum efficiency.