Gas water heater buying guide
Finding the right gas water heater starts with understanding your options. Tank size, efficiency, venting and installation requirements all play a role in selecting the best model for your customer’s home.
This guide explains the different types of gas water heaters, what to know before installation, key parts and accessories, and the features that can help improve performance and energy savings.
Types of gas water heaters
Gas water heaters come in several sizes, each designed for different budgets, hot water needs and installation requirements.
Standard efficiency tank water heaters
Standard gas water heaters store hot water in an insulated tank and use a gas burner to keep it heated. They're a reliable, cost-effective choice for many homes and are often the easiest option when replacing an existing gas water heater.
Best for:
Replacing an older gas water heater
Homes with average hot water use
Lower upfront costs
Existing atmospheric vent systems
High-efficiency (condensing) tank water heaters
High-efficiency gas water heaters capture more heat before it leaves the unit, helping reduce energy use over time. While they typically cost more upfront, the improved efficiency can lead to lower utility bills.
Best for:
Homeowners looking to save energy
Homes with higher hot water demand
New construction
Long-term operating savings
Tankless gas water heaters
Tankless gas water heaters heat water only when it's needed instead of storing it in a tank. Because they don't run out of stored hot water (as long as they’re properly sized), they're a popular option for larger households and homes with high hot water demand.
Best for:
Larger families
Homes with limited space
New construction and remodels
Continuous hot water
Gas water heater code requirements
Residential
Residential gas water heater installations must meet local plumbing, gas and mechanical codes to help ensure safe and reliable operation. While specific requirements vary by geography, most installations require:
Approved venting
Drain pan in certain locations
Proper combustion air
Commercial
Because commercial gas water heater systems are often designed to support higher hot water demand, they may have additional plumbing, gas and energy code requirements. Depending on the application, these installations may include:
Larger gas supply
Higher recovery rates
Multiple water heaters configured together
Recirculation systems
Additional code requirements
Low NOx vs. Ultra-Low NOx
Some states and municipalities, particularly western states, require water heaters that produce fewer nitrogen oxide (NOx) emissions.
Low NOx models meet many local air quality standards.
Ultra-Low NOx models reduce emissions even further and may be required in certain areas.
Gas water heater installation and placement
Choosing the right location can make installation easier and simplify future maintenance.
Space requirements
Leave enough room around the water heater to access the burner, controls, anode rod, and other serviceable parts. As the industry standard size of water heaters has grown substantially over time, it’s more important than ever to follow the manufacturer's recommended clearances.
Gas line requirements
Before installing a new gas water heater, make sure the existing gas line can supply enough fuel. Higher-capacity and high-efficiency models may require larger gas piping.
Natural gas vs. propane
Gas water heaters are designed to run on either natural gas or propane (LP). Be sure to choose the correct fuel type for the installation.
Condensate management
High-efficiency condensing models create condensate that must be drained properly — and a properly installed condensate pump may be needed to move the condensate to an approved drain location, particularly when gravity drainage isn't possible. Depending on local code, a condensate neutralizer may also be required.
Water connections
Check the hot and cold water connections to make sure they align with the new unit’s specs and inspect shutoff valves for any signs of wear or leaks that could be problematic. Thoroughly assessing the entire plumbing layout before installation helps to ensure smooth installation and replacement, when necessary.
Sizing gas water heaters
Choosing the right size gas water heater helps ensure a reliable supply of hot water while maximizing energy efficiency. For tank water heaters, consider the household size and the unit's First Hour Rating (FHR), which estimates how much hot water the heater can deliver during peak demand. For tankless gas water heaters, sizing is based on the required flow rate (gallons per minute) and the temperature rise needed to deliver hot water to one or more fixtures at the same time. Selecting the right size helps prevent running out of hot water while avoiding unnecessary energy use.
Replacing an electric water heater
Switching from an electric water heater to a gas water heater usually requires adding a gas line, installing venting, and confirming there's enough combustion air for safe operation.
New construction
Installing a gas water heater during new construction allows you to plan gas piping, venting, and plumbing for easier installation and future service.
Gas water heater venting
Proper venting removes combustion gases safely and helps your water heater perform as intended.
Atmospheric venting
Atmospheric vent water heaters use a natural draft to vent exhaust gases through a vertical vent or chimney. They're a cost-effective option for replacing existing standard gas water heaters in homes with compatible venting already in place, often making installation simpler and more affordable.
Power venting
Power vent water heaters use a fan to push exhaust gases through vent piping, providing greater installation flexibility than atmospheric vent models. Since many models allow for horizontal venting, power vent water heaters are a good choice for finished basements, remodeling projects or homes where a traditional vertical vent isn't practical — especially when longer vent runs are needed.
Direct venting
Direct vent water heaters pull combustion air from outside and vent exhaust through a sealed system, making them a good option for tightly sealed homes or spaces with limited indoor air. They're commonly installed in areas where bringing in outside air helps support safe, efficient operation. Depending on the model, direct vent systems may also accommodate horizontal vent runs when vertical venting isn't ideal.
Power direct venting
Power direct vent water heaters combine sealed combustion with a powered fan to provide the greatest flexibility for venting. They're well suited for high-efficiency installations, new construction, and projects with longer or more complex venting requirements. Many models support longer horizontal vent runs, making it easier to accommodate challenging layouts and maximize installation flexibility.
Gas water heater parts and accessories
Knowing the main parts of a gas water heater can help make maintenance and repairs easier.
Anode rods
Anode rods help protect the inside of the tank from corrosion by attracting corrosive minerals before they can damage the tank itself. Because anode rods are designed to sacrifice themselves over time, they should typically be inspected every one to three years and replaced every three to five years, depending on water quality and usage. Homes with hard water, water softeners or high hot water demand may require more frequent inspections. An anode rod may need replacement if the hot water is rust-colored or cloudy, emits a rotten egg odor, or if there’s visible corrosion and significant wear when it’s inspected.
Choosing the right anode rod can help extend the life of a water heater and improve long-term performance.
Anode rod options include:
Magnesium: Excellent corrosion protection
Aluminum: Better suited for hard water
Zinc: Helps reduce sulfur odors
Powered: Long-lasting, maintenance-friendly protection
Heat exchangers
Heat exchangers transfer heat from the burner to the water and play a major role in the efficiency of tankless and high-efficiency gas water heaters. Depending on the model, they may be made from stainless steel or copper to provide durability, corrosion resistance, and reliable performance.
Ignition systems
Gas water heaters use either a standing pilot or an electronic ignition system to light the burner. Standing pilots always remain lit, while electronic ignition systems ignite the burner only when hot water is needed, helping improve energy efficiency, and reduce gas consumption.
Gas control valve
The gas control valve regulates the flow of gas to the burner and helps maintain the desired water temperature. It also incorporates important safety features that help ensure the water heater operates safely and efficiently.
Burners
The burner heats the water inside the tank or heat exchanger. A burner’s design can affect recovery rates, fuel efficiency, and emissions. Many newer models feature advanced burners that deliver improved performance while meeting current emissions standards.
Tank lining
Most gas storage water heaters feature a glass-lined steel tank that helps protect against corrosion and extend the life of the unit. Combined with a properly maintained anode rod, the tank lining provides an important layer of protection against everyday wear. While you can replace components like the anode rod or perform maintenance to remove sediment, the tank lining cannot be repaired or relined once it deteriorates.
T&P relief valve
The T&P relief valve releases pressure if the water heater becomes too hot or pressure builds inside the tank. It should always be installed with an approved discharge pipe and inspected periodically to help ensure proper operation.
Discharge pipe
The discharge pipe carries water safely away from the T&P relief valve if it opens. It should be installed to help prevent injury or water damage if the relief valve activates.
Expansion tank
An expansion tank helps absorb pressure caused by heated water expanding inside a closed plumbing system, but these components eventually fail and require replacement due to issues like internal rubber bladder ruptures, waterlogging caused by lost air charge, and metal corrosion that leads to leaks over time.
Drain pan
A drain pan sits beneath the water heater to help protect floors and surrounding areas from leaks. It's commonly required when a water heater is installed in an attic, closet or other finished space where water damage could occur. To further elevate the unit off the floor for safety compliance or easier drainage, pair these pans with a sturdy water heater stand.
Advanced gas water heater features
Many of today’s gas water heater models include advanced technologies that improve energy efficiency, simplify installation and make maintenance easier. Depending on the model and manufacturer, these features can also help reduce service calls, improve performance and enhance the overall user experience.
Built-in recirculation
This Rinnai SENSEI™ RX Series 199 MBH Smart Indoor Condensing Natural Gas/Propane tankless water heater includes the brand’s Smart Circ™ Intelligent Recirculation™ — a great example of recirculation technology included in some gas water heaters to deliver hot water to fixtures faster while reducing water waste.
Wi-Fi and Bluetooth connectivity
Many gas water heaters, like Rheem’s IKONIC™ water heater, include Wi-Fi and Bluetooth connectivity that allow customers to monitor performance, adjust temperature settings, and receive maintenance alerts through a mobile app.
Leak detection and automatic shutoff
Units with leak detection catch leaks early and may automatically shut off the water supply to help minimize water damage.
Freeze protection
Available on many tankless models, freeze protection helps to protect internal components in colder climates.
Scale prevention technologies
Some units, like this tankless water heater from State, come with built-in scale prevention technology that helps to reduce mineral buildup inside the heat exchanger, improving efficiency and extending its lifespan.
Whether you're replacing an older gas water heater, upgrading to a high-efficiency model or installing a tankless system, shop from Ferguson’s vast water heater collection and choose from top-of-the-line gas tank water heaters, tankless water heaters and replacement parts from trusted brands, along with the accessories needed for installation and maintenance. Ferguson makes it easy to find the right gas water heater for your next project.