Gas Water Heaters Review
Buying Guide

Searching for the gas water heaters? Compare the tank-type heaters vs. tankless heating, and explore the main components, differences, and advantages. Who are the top manufacturers?


There are two types of gas water heaters:

Tank-type gas water heaters

ao smith gas water heaterGas hot water heaters with the storage tank are designed to provide a large volume of hot water. 50-gallon tank size is one of the most popular sizes as it provides sufficient amount of hot water for the family size of 4 to 5.

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.

This type of water heating is the most popular in North America, while tankless heaters are mainly used in Germany, Italy, France, UK, Japan...

How tank-type water heater works

Hot water is always ready in the tank-type heaters. Even when there is no demand for hot water (i.e. the tap is open) 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 the signal to the gas control valve to open.

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

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

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

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

Where to use gas water heaters with the storage tank

Tank-type, gas powered water heaters 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 will usually be installed in a garage, attic, basement or technical room, but it 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.

Gas water heaters types

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

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

Direct vented 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 the air intake.

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


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

The first three manufacturers from the above list are the largest manufacturers in North America while other manufacturers or brands are their subsidiaries or re-brand.

The main components

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

  • Metal tank with the glass lining for protection

  • Foam insulation to reduce the stand-by heat loss

  • Draft diverter on atmospheric type heaters

  • Power vent on power vent models

  • Flue baffle

  • Gas control valve with the thermostat

  • Pilot light

  • Thermocouple

  • Dip tube

  • Anode rod

  • Drain valve

  • TPR valve

  • Burner assembly

Tankless type gas water heaters

vaillant gas water heaters tanklessGas powered tankless water heaters in last decade or so, are getting more and more on popularity. Their main advantages are an endless hot water, on-demand heating, small and compact size and 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 the single unit; some brands, such as Noritz, can provide high 11 gallons per minute or work as the multi-system (some manufacturers offer features to connect up to 24 units into one system).
Tankless heaters are also using 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 the energy efficiency to over 90% and provides great savings.

The 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...)


Tank vs tankless

  • Water tank heaters are cheaper than tankless and the installation and venting costs are lower.

  • Some tank-type units do not require electricity.

  • Flow rates are higher on storage tanks.

  • Tankless provide an endless fresh water supply.

  • Tankless are smaller, wall mounted and do not occupy floor space. Some tankless models can be installed in the bathroom, kitchen...

  • Low operating costs.

  • Indoor and outdoor models available.

  • Energy efficiency is higher.

  • Advanced electronic system for the precise temperature control and troubleshooting.


When searching for the gas water heaters, my recommendation is to look for the high efficiency and Energy Star approved models. They save energy, do the work efficiently and provide savings with the 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 higher recovery rate, costs less to operate and offer a wider line of products.


Pictures are courtesy of A.O. Smith and Vaillant

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