Gas Water Heaters: Review and Buying Tips

Are you searching for the best gas water heaters?

Compare tank-type vs. tankless heating, explore the main components, differences, and advantages, learn how they work, discover the top manufacturers, find a buying and sizing guide, and get installation and maintenance tips. Plus, explore the gas vs. electric options with pros and cons.

Gas water heaters: Things to consider

  1. Types
  2. Storage tank-type
  3. Tankless
  4. Tank vs. tankless
  5. Gas vs. electric
  6. Sizing tips


Gas-powered water heaters come in several types, each with its own set of advantages and considerations. Here are some of the most common types:

  • Storage tank
  • Tankless
  • Combination type (used for both heating the potable water and space)

Tank-type gas water heaters

Gas water heaterGas water heater

Gas water heaters with a storage tank-type are the most common and popular type in North America. The main purpose of the storage water tank is to store hot water, and it usually comes with the capacity ranging from as low as 2 gallons to over 100 gallons. Heaters with a smaller capacity such as 20 gallons and less, are mainly designed for point-of-use service and a single application.

Larger heaters are built for the whole-house use, and those with a capacity from 50 to 80 gallons are the most popular - they provide a sufficient amount of hot water for families with 4-5 members. Most of the tank-type models are designed simply with the average energy efficiency of 0.60, while the advanced models come with condensing technology and have ultra-high energy factors. A great example is Vertex from AO Smith.

AO Smith Vertex (sold by Amazon) is the best tank-type from this manufacturer and it comes with an efficiency of over 90%, stainless steel heat exchanger and environment-friendly gas burner.

Most of the available gas water heaters utilize natural gas, but if this fuel source is not available, the unit can be converted to use propane gas instead.

Water heating with tank-type heaters is the most popular in North America, while tankless heaters are mainly used in Germany, Italy, France, UK, and Japan.

How does it work

Gas tank-type water heaterGas tank-type water heater - Inside

Hot water is always ready in tank-type heaters. Even when there is no demand for hot water a tank-type heater must cycle periodically to maintain the set temperature. If the water temperature inside the heater's tank drops below the set value, the thermostat sends a signal to the gas control valve to open.

Then, the pilot flame lights the gas inside the combustion chamber, which then heats the water. When small draws are made, the gas burner does not usually fire.

Cold water is coming into the tank through the inlet pipe or dip tube, while the hot water rises up and goes to the open hot water tap through the outlet pipe.

Products of gas combustion are then traveling through the venting system and out, either naturally or forced by the blower.

Selecting the right size of the gas water heater should be done by considering your family size and other factors. Keep in mind that the tank has about 70% of the usable space, so if you have a 50-gallon gas model, the tank can store 35 gallons.

A detailed explanation of how tank-type and tankless gas water heaters work can be found in this article.

Where to use gas water heaters with the storage tank

Tank-type and gas-powered water heaters for the whole house heating can be found in sizes from 20 gallons to over 100 gallons. These heaters can be used in residential, commercial applications, and manufactured or mobile homes.

The residential heater is usually installed in a garage, attics, basements or utility rooms, and its location depends on the room space and installation requirements. Tank-type gas hot water heaters cannot be installed in the bathroom or bedrooms and must be installed indoor as close as possible to the outside wall or chimney.

Venting options

Based on how flue gases are vented out, gas hot water heaters are designed as atmospheric, direct, power or power-direct vented units. They must be installed per codes and manufacturer's instructions.

Each type is designed for different house type, and location of the unit has to take into account the type.

Atmospheric vented models are the most common type. The vent runs vertically, above the roof-line and are using the vertical standard B type vent or masonry chimney.

Direct vented (DV) heaters do not use the electrically powered blower and chimney. They have a sealed combustion chamber and two pipes; one for extracting gases out and one for air intake, from the outside.

Power vented (PV) units utilize a blower to move the flue gases out. This type is more flexible than the atmospherically vented heaters, as the vent can run vertically or horizontally and through the roof or wall. The heater can also be at the certain distance from the termination point, but it is more expensive.

Power direct vent models (PDV) are used in homes that lack sufficient air for gas combustion. Since the inside air cannot be used for combustion, the air is drawn from outside using a vent pipe while the electric blower moves the flue gases out. They are also used in homes that require flexible installation, such as when longer vents are required. The venting pipes can run either horizontally or vertically.

For more information on venting types, layout, problems, and installation tips, refer to the resource provided here.


The most popular manufacturers of tank-type gas hot water heaters are:

Note: AO Smith, Rheem and Bradford White manufacturers from this list are the largest manufacturers in North America while other manufacturers or brands are their subsidiaries or re-brands.

Main components

When comparing the above brands, you will see that they have many similar parts. Of course, the quality varies. The elements shown below can be found in the majority of today's gas water heaters:

Tankless-type gas water heaters

Rinnai tankless water heaterTankless

In the last decade or so, gas-powered tankless water heaters have become increasingly popular. The main advantages are endless hot water, on-demand heating, small and compact size as well as wall mounted installation.

Tankless gas water heaters can provide hot water for any home size or application, but it depends on the model and installation options. They can work as a single unit where some brands such as Noritz NRC1111, can provide the high flow rate of 11 gallons per minute and function as the multi-system (some manufacturers offer features to connect up to 24 units into one system).

Tankless heaters are also use natural gas and propane (LPG) gas as the tank-type. These on-demand units are more energy-efficient than conventional tank-type heaters, as they don't have a standby heat loss. They produce fewer greenhouse gases, and that is why they are called "green."

More advanced gas water heaters are using condensing technology, which increases energy efficiency to over 90% and provides significant savings. A great example is Rinnai RUR98. 

When you buy Rinnai RUR98 (sold on Amazon) you will get a superior device with the efficiency of 96%, the most innovative electronics, recirculation, Wi-Fi connectivity and more.

Tankless water heaters are much smaller than the above tank-type and are usually wall-mounted. Instead of heating water stored inside the tank, they use on-demand technology that utilizes heat exchangers, delivering an endless supply of hot water when needed. Efficiency is much higher.

Main components

  • Heat exchanger - most of the tankless heaters have one exchanger while condensing have two
  • Power or direct venting
  • Gas burner
  • Gas valve
  • Electrodes for lighting
  • Electronic board
  • Control panel
  • Sensors (flow, temperature...)

Tankless water heaters, also known as on-demand water heaters, have a relatively simple but efficient design. They consist of several key components that work together to provide hot water whenever it's needed.

Here are the main components of a tankless water heater:

  • Water Inlet: Cold water enters the tankless water heater through a dedicated inlet pipe. This incoming water flows through the unit to be heated as it moves through the system.
  • Flow Sensor: The flow sensor is a crucial component that detects when hot water is needed. It senses the water flow rate and activates the heating element when there is a demand for hot water. If there is no flow, the heater remains off to conserve energy.
  • Heat Exchanger: The heart of the tankless water heater is the heat exchanger. This component is responsible for heating the incoming cold water. There are two main types of heat exchangers: 

Coil-Type Heat Exchanger: In this design, the water passes through a coil of heated pipes or elements. As water flows through the coil, it absorbs heat from the heating elements, raising its temperature.

Plate-Type Heat Exchanger: This design uses a series of plates with small channels. Cold water passes through one set of channels, while hot water or a heating element passes through the adjacent channels. Heat is transferred from one side to the other through the plates.

  • Burner or Heating Element: For gas-powered tankless water heaters, there is a gas burner that ignites when hot water is needed. It heats the water as it flows through the heat exchanger. Electric tankless water heaters use heating elements similar to those found in traditional electric water heaters to heat the water.
  • Temperature Control and Safety Devices: Tankless water heaters are equipped with temperature sensors and control systems to maintain the desired hot water temperature. Safety devices, such as pressure relief valves and overheat protection, are also included to ensure safe operation.
  • Venting System (Gas Heaters): In gas-powered tankless water heaters, there is a venting system to remove combustion gases and byproducts. The type of venting (direct vent, power vent, or ventless) depends on the specific model and installation requirements.
  • Water Outlet: The heated water exits the tankless water heater through a dedicated outlet pipe, ready for distribution to faucets, showers, or appliances.
  • Digital Controller/Display: Many tankless water heaters have a digital controller or display that allows users to set and monitor the desired water temperature, check for error codes, and adjust settings.
  • Air Intake (Gas Heaters): For gas tankless water heaters, there is an air intake that provides oxygen for combustion. It's essential to ensure proper airflow for efficient and safe operation.


Tank vs. tankless

  • Water tank heaters are cheaper than tankless while installation and venting costs are lower.
  • Some tank-type units do not require electricity.
  • Flow rates are higher on storage tanks.
  • Tankless provides endless and fresh supply of hot water.
  • Tankless are smaller, wall mounted and do not occupy floor space. Some tankless models can be installed in the bathroom or kitchen.
  • Tankless have low operating costs.
  • Indoor and outdoor models are available.
  • Energy efficiency is higher on tankless.
  • An advanced electronic system for the precise temperature control and diagnostics.

More about tank vs. tankless here.

Gas vs. electric

  • Gas heats water faster.
  • Gas-powered quick-recovery water heaters offer more capacity for the same tank size.
  • Gas models are Energy Star compliant.
  • Gas heaters have lower operating costs.
  • Some gas models do not require electricity to operate.
  • Electric models are more straightforward and cheaper.
  • Electric units have lower installation costs.
  • Electric models are safer.
  • There is no venting in electric models.
  • Electric has higher energy efficiency but is not Energy Star.

Sizing tips

When you are choosing a gas water heater, it is essential to do proper sizing, so the unit can meet the needs/demand of the whole household. The size of the water heater (capacity in gallons) depends on the number of people in your home and how many applications are to be used at the same time.

Check the Energy Guide label of the gas water heater to determine the First-Hour Rating (FHR). It is essential to have the FHR number higher to get enough hot water during the peak hour. The first-hour rating is the measure of how much hot water the unit will deliver during the peak time.

If your family consists of 1-2 people, a 40-gallon unit is sufficient. For 3-5 people, choose a 50-gallon unit, and for more people, select a water heater with 60 gallons or more.

Use the sizing chart below to see how much water is used per application:

  • Shower - 10 gallons
  • Bath - 20 gallons
  • Dishwasher - 6 gallons
  • Washing machine - 7 gallons
  • Shaving - 2 gallons


When searching for the gas water heaters, the recommendation is to look for the high energy factor - EF or UEF, Energy Star approved models and high first-hour delivery or water flow rate (GPM). They save energy, work efficiently, and provide savings with lower consumption, government grants, and utility company rebates.

When comparing gas vs. electric, gas powered heaters are a better solution as they heat water faster, have a higher recovery rate, cost less to operate, and offer a better selection of products.


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