A 40-gallon gas water heater can be a practical replacement when you need a similar tank size, but the right choice depends on more than capacity. Check whether your home uses natural gas or propane, confirm the venting setup and available space, and make sure the model is approved for your installation. The options below include standard atmospheric units, a propane model, and a direct-vent heater designed for mobile homes.
Table of Contents
Quick Comparison
| Water heater | Fuel and vent type | Standout details | Best fit |
|---|---|---|---|
| GE RealMAX Choice 40-Gallon Tall Natural Gas Atmospheric Water Heater | Natural gas, atmospheric | Tall 40-gallon tank | Homes set up for a tall atmospheric natural gas unit |
| Rheem Professional Classic 40-Gallon Atmospheric Water Heater | Natural gas, atmospheric | 38,000 Btuh input | Shoppers seeking a specified-input natural gas option |
| A. O. Smith GCR-40LP ProMax Plus | Liquid petroleum gas | Electronic gas valve and corrosion-resistant tank coating | Homes configured for propane |
| Reliance 6-40-MDV400 Mobile Home Direct Vent Water Heater | Gas, direct vent | Mobile-home design, direct pipe system, 2-inch insulation | Compatible mobile-home installations |
Our Picks: Best 40 Gallon Gas Water Heater reviews
GE RealMAX Choice: A Tall Atmospheric Natural Gas Option
The GE RealMAX Choice is a 40-gallon, tall-tank water heater that uses natural gas and atmospheric venting. Those details make it a candidate for a replacement installation that already supports this fuel and vent style. A tank’s capacity alone does not guarantee a fit, so check the unit’s dimensions and the requirements for your existing space before ordering.
The product information supplied for this model is limited to its capacity, tall form, fuel, and vent type. It does not provide details such as burner input or additional construction features, so compare the full manufacturer specifications with your installation needs rather than assuming the models are otherwise alike.
This is the simplest match in the group if you specifically need a tall atmospheric natural gas model. It is not the right choice for a propane connection or an installation that requires direct venting. The listing may also have limited availability, so confirm the seller’s current status before planning a replacement around it.
Pros:
- 40-gallon capacity in a tall design
- Uses natural gas
- Atmospheric venting is clearly identified
Cons:
- Available product details are limited
- Not suitable for propane or direct-vent-only setups
Verdict: Consider the GE if your home needs a tall, atmospheric natural gas heater and the full specifications match your space and venting.
Rheem Professional Classic: Natural Gas with 38,000 Btuh Input
This Rheem Professional Classic is a 40-gallon tall atmospheric water heater for natural gas. Its listed 38,000 Btuh input gives you a useful specification to compare with your existing unit or an installer’s recommendation. The product description also identifies it as a durable model, but it does not provide more detail about the construction or a specific performance comparison.
Like the GE, this unit is aimed at a home with natural-gas service and compatible atmospheric venting. The fuel and vent type matter more than the brand name: this model is not a direct substitute for a propane heater or a direct-vent unit unless the installation is specifically changed and approved by a qualified professional.
The supplied product title includes the word “Side,” but does not explain what that refers to. Confirm the complete model specifications and connection layout before purchase, especially if you are replacing a heater in a tight space.
Pros:
- 40-gallon capacity and tall design
- Natural gas atmospheric configuration
- 38,000 Btuh input is listed for comparison
- Product information describes it as highly durable
Cons:
- Requires compatible natural gas and atmospheric venting
- Some installation details are not clear in the supplied product information
Verdict: The Rheem is a practical candidate when you want a tall, 40-gallon atmospheric natural gas model and its input and connection details suit your setup.
A. O. Smith ProMax Plus: A 40-Gallon Propane Heater
The A. O. Smith GCR-40LP is a 40-gallon heater designed for liquid petroleum gas, commonly called propane. Its fuel type is the key distinction: it should be considered only where the home’s gas supply and installation are set up for propane. Do not choose it as a direct replacement for a natural gas heater based on tank size alone.
The listed features include a Blue Diamond glass coating intended to resist corrosion, a self-powered electronic gas valve, and an internal microprocessor for sensing and control. Its Dynaclean diffuser dip tube is described as helping reduce lime and sediment buildup while supporting hot-water output. These features make the model more detailed on paper than the GE option, though they do not remove the need to confirm fit and installation requirements.
The main limitation is compatibility. This model is for liquid petroleum gas, not a universal gas heater. The supplied listing also indicates it may not currently be available, so check the listing and consider other suitable propane models if you need a replacement soon.
Pros:
- 40-gallon capacity for propane installations
- Blue Diamond glass coating is designed for corrosion resistance
- Self-powered electronic gas valve and internal microprocessor
- Diffuser dip tube is designed to help limit lime and sediment buildup
Cons:
- Not the right fuel type for natural gas service
- Listing availability may be limited
Verdict: Choose the A. O. Smith only if your installation calls for propane and the full model specifications are a match.
Reliance Mobile Home Direct Vent: A Specialized Installation Choice
The Reliance 6-40-MDV400 is a 40-gallon direct-vent water heater designed for mobile-home use. The listing specifies a direct pipe system, an aluminum anode rod, and 2-inch insulation. It also gives dimensions of 58-3/4 inches high by 20 inches in diameter, which can help you begin checking the available space.
This model is more specialized than the standard atmospheric options above. Its mobile-home designation and direct-vent arrangement mean you should verify that both the heater and its venting method are approved for your particular home. A similar tank capacity does not make it interchangeable with a conventional atmospheric heater.
The supplied product information does not specify the fuel type, so confirm that detail in the full manufacturer documentation before purchase. The stated dimensions are also only part of a fit check; allow for the required clearances, pipe connections, and access needed for installation.
Pros:
- Designed for mobile-home installations
- Direct-vent design with a direct pipe system
- 2-inch insulation is specified
- Dimensions are listed for initial space planning
Cons:
- Specialized design may not suit a conventional home installation
- Fuel type is not specified in the supplied product information
Verdict: The Reliance is worth considering for a compatible mobile home that requires this direct-vent format, but confirm fuel, clearances, and installation approval first.
How to Choose a 40-Gallon Gas Water Heater
Match the fuel to your home
Natural gas and liquid petroleum gas models are not interchangeable just because they have the same tank capacity. Check the fuel supply used by your current heater and verify the replacement’s fuel type in its complete product documentation. If you are unsure, ask a qualified installer to identify the connection before you order.
Confirm the venting style
Atmospheric and direct-vent models use different venting arrangements. A heater designed for one setup may not work as a replacement for the other. Check the existing vent, the manufacturer’s installation instructions, and local requirements. The GE and Rheem options listed here are atmospheric models, while the Reliance is identified as a mobile-home direct-vent unit.
Measure the space and connections
Measure the height, width, and access path to the installation area. Compare those measurements with the manufacturer’s specifications, and account for the clearances and connections the installation requires. The Reliance listing provides dimensions, but the other product details supplied here do not include full measurements, so look them up before buying.
Think about hot-water use, not just tank size
A 40-gallon tank may be a reasonable replacement when your existing system is similar, but the right capacity depends on how your household uses hot water. Consider when showers, laundry, and dishwashing tend to overlap. Ask an installer to check whether a 40-gallon model and its input are appropriate for your needs rather than relying on capacity alone.
Compare the specifications that matter to your replacement
Look at fuel type, vent type, tank dimensions, input, and connection layout. The Rheem listing specifies 38,000 Btuh, while the A. O. Smith listing describes several gas-control and tank features. The GE listing provides fewer details, so you may need to consult the full specifications before making a direct comparison.
Check installation rules and availability
Water-heater installation can involve fuel, venting, and local code requirements. Confirm that the selected model is permitted for your home and that a qualified installer can work with its configuration. Product availability can change, so check the listing before you make plans or schedule installation.
Frequently Asked Questions
Is a 40-gallon gas water heater enough for a household?
It depends on how much hot water your household uses and whether several fixtures run at once. Consider your busiest periods and have an installer confirm whether a 40-gallon tank is a suitable size for your home.
Can I replace a natural gas heater with a propane model?
Do not assume you can. The A. O. Smith model listed here is designed for liquid petroleum gas, while the GE and Rheem models are identified as natural gas units. Match the heater to your home’s fuel setup and follow the manufacturer’s requirements.
Can an atmospheric heater replace a direct-vent model?
Not automatically. Atmospheric and direct-vent heaters use different venting arrangements. Confirm the replacement’s venting requirements and get professional guidance before changing the type of unit.
What does “tall” mean when comparing water heaters?
It describes the tank’s form, but it does not tell you whether it will fit your installation. Check the model’s complete height and diameter measurements, plus the required clearances and connection locations.
Is the Reliance model suitable for any home?
The listing identifies it as a mobile-home direct-vent water heater, so it is a specialized option. Confirm that your home and venting system are approved for that model before buying.
Which model has the most detailed listed features?
The A. O. Smith listing provides the most detail about tank coating, gas control, microprocessor operation, and its diffuser dip tube. Those features do not make it a fit for every home; it is identified as a propane model, so fuel compatibility comes first.
Final Recommendation
For a standard atmospheric natural gas replacement, compare the GE RealMAX Choice and Rheem Professional Classic against your current unit’s dimensions, venting, and specifications. The Rheem listing provides a 38,000 Btuh input figure, while the GE listing identifies a tall 40-gallon format. Choose the A. O. Smith only for a compatible propane setup, and consider the Reliance only where its mobile-home direct-vent design is appropriate. When fit, fuel, or venting is uncertain, verify the model with a qualified installer before purchasing.
