Gas Hot Water Heaters

Gas powered tank and tankless water heating systems

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Gas hot water heaters are high efficient, high performing and environment friendly systems, a great choice for the homeowners, when buying a brand new or upgrading an existing water heater. Even if you already have an electric, you might want to switch to gas, because of all the benefits and savings natural gas or propane water heating brings.

This review and provided links is about gas water heating, propane and natural gas water heaters, maintenance and tips when buying, covering both storage tank-type and tankless models. We will also review the most popular manufacturers, provide installation and maintenance tips, present most common problems and help you with the troubleshooting.

Natural gas or propane - LP

Either you are buying a tank-type or gas tankless water heater you can use both natural gas and propane - LP, as long as you have this fuel available. The location of the gas hot water heaters in the home may be restricted by access to the fuel supply line.

To run propane water heaters, you need liquid propane, LP, storage tank and regular fuel delivery. The performance is similar to natural gas water heaters.

When comparing natural gas vs. propane, or LP, energy factor EF is almost the same for most brands of gas heaters.

When using natural gas as a fuel option, you can also have a common heating unit that provides heating for your home and hot water delivery.

In both cases, both tank type and tankless gas heaters produce hot water very quickly.

Selecting a gas water heater - Things to consider

Determine the size you need

gas hot water heaters

Free standing, storage or tank gas hot water heaters are usually installed in a designated room, while tankless, such as the popular Rinnai R75LSi, because of its small size and venting options, almost anywhere.

The popular sizes of tank type gas hot water heaters are 40-gallon and 50-gallon as they are sufficient for a family of 4-6 and middle size homes with up to two, three bathrooms. Check out the prices of 50-gallon water heaters here, on

Select the best venting option

Another important factors when buying gas hot water heaters, installing or troubleshooting, are the options your have for the efficient and economical venting.

When gas water heater is running, it requires an air for combustion and igniting, where the air can be used either from the household or from the outside. On the other side, it is also important and for safety reason, conveying the flue outside, either by natural draft or by powered vents.


  • Conventional, atmospheric vent is using chimney.

  • Direct vent, no chimney and blower needed, it vents directly out through the wall by using the provided vents.

  • Power vent is like direct vent but with a help of electrically power vent - blower.

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Gas versus electric water heaters

  • Heating with gas is two times faster than the electric units.

  • Higher recovery rate. 50-gallon gas hot water heater has the average recovery rate of 80-90 GPH while electric 50-gallon size has recovery rate of approximately 60 GPH.

  • It costs less to operate than the electric units.

  • They are high efficient by design.

  • There is a variety of products, from tank heaters, to tankless and combination of gas fired burners and tank type heaters.

  • Ultra efficient, condensing models available.
Money saving tip: If gas hot water heaters are expensive for you, you can always rent one. Renting the water heater gives you a peace of mind and if anything goes wrong with the unit most parts and service are covered.

If planning to switch from an existing heating system to new one, using a natural gas or propane, consider next:

  • It is easy to convert to natural gas hot water heater.

  • If there is no chimney, direct or power vented heaters are your best bet.

  • If the chimney already exist, it has to be checked by a professional, and if it is needed perform cleaning or resizing. Other option is to use direct or power vent system which does not require chimney.

  • It is also very easy to replace an existing and old natural gas water heater with a newer one, but first check the venting options in a home.

  • Older heaters are less energy efficient.

Tank type gas hot water heaters - Main parts

  • Water tank to store the water

  • Glass lining for metal tank protection against corrosion.

  • Draft hood for flue tube installation.

  • Flue Tube to remove the products of combustion out.

  • Dip Tube for bringing the cold water inside the tank.

  • Drain Valve for draining water during maintenance (for example).

  • Gas combustion chamber.

  • Electric blower on power units to remove the gases out.

  • Thermostat to control the temperature of hot water.

When comparing gas water heater parts vs. electric, you will see that gas heaters, both tank type and tankless have much more components where some of them are complex and expensive, like the valve or venting on tankless units.

How tank type works

Once the hot water tap is open, hot water from the top of the tank starts running through the hot water outlet to the faucet or shower. At the same time cold water enters from the bottom through the dip tube.

Thermostat senses the cooler water and turns on the gas at the gas valve and the burner that is mounted at the base of the tank. Thermocouple as a safety element sends the signal to the gas valve to open - only if there is a presence of a pilot flame to lit the gas. Once the flame is established, water is heated and the product of combustion from the combustion chamber are removed through the flue vents out.

More tips when shopping for gas hot water heaters

One third of energy in North American home is accounted for water heating, while showers alone use as much as one-third of all household water. When buying a gas hot water heater, look for one with high energy factor - EF, such as condensing.

Tip: Check out the Energy Factor, EF. If EF is 0.82 or higher on tankless heaters or 0.67 on tank type we are talking about high efficiency heaters. They have a blue tag with a name Energy Star on it. If you buy one Energy Star unit there is a rebate through the government tax credit grants.

Energy factor is used to express the efficiency of natural gas, propane and oil fired heaters; higher better. Don't forget that when selecting an oversize tank heater the energy cost goes up as the standby loss increases.

Which gas water heater to buy?

ao smith high efficiencyIf looking to buy the best tank-type gas heater, buy AO Smith GDHE-50-NG Vertex 100 or Polaris Water Heater, both with approximately 96% energy efficiency, one of the highest EF among gas powered tank heaters.

My recommendation for tankless condensing water heaters is Rinnai RC80HPi that comes with the great EF factor of over 0.9.

In a case of the electric water heaters, only heat pumps, such as RHEEM HP50RH and GE GeoSpring are Energy Star qualified.

Recommendation is to buy high efficient models - they provide higher quality, have better warranties and pay off in the long run.

  • The capacity of gas water tank heaters is based on the number of gallons that will fit in the tank.

  • Tankless models are rated by how many gallons of hot water they produce per minute (GPM). With more applications comes the higher GPM. Here is how much an average home spends hot water.

  • Clothes washer - 3.3 GPM

  • Shower and bathtub - 2.5 GPM

  • Kitchen and bathroom sink - 2.2 GPM

  • Dishwasher - 1.3 GPM

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(All pictures are courtesy of AO Smith and BW)