The best gas hot water heaters deliver plenty of hot water for busy households and recover quickly when everyone showers in the morning. Tankless gas hot water heaters have become popular because they provide continuous hot water and save space. In this comparison, we look at two Rheem tankless models sized for different homes.
Our picks: the Rheem RTG-84XLN-3 (8.4 GPM) for large households and the Rheem RTG-70DVLN-3 (7.0 GPM) for medium-size homes.
Best Gas Hot Water: Top Picks Compared
Our top picks are the Rheem RTG-84XLN-3 8.4 GPM Natural Gas Tankless and the Rheem RTG-70DVLN-3 7.0 GPM Natural Gas Tankless.
Pros
- Exceptional energy efficiency reduces monthly utility bills significantly compared to tank heaters
- Hot Start Programming solves the common tankless water heater problem of initial cold water delays
- Compact 13.5-inch width and wall-mount design saves valuable floor space in tight installations
- Comprehensive warranty protection with 15-year heat exchanger coverage provides long-term peace of mind
- Stainless steel construction and overheat protection ensure reliable performance and durability
Cons
- Professional installation is required, adding to initial setup costs beyond the unit purchase price
- Initial delay before hot water arrives is common with tankless units despite Hot Start Programming
- Outdoor installation only limits flexibility for homes needing indoor water heater placement
The Rheem RTG-84XLN-3 is a high-capacity natural gas tankless water heater designed for large families and multi-bathroom homes. With its 8.4 GPM flow rate and 180,000 BTU output, this unit can handle 3 to 4 simultaneous showers without running out of hot water, making it an excellent choice for households that demand consistent performance.
The standout feature is the Hot Start Programming technology, which keeps the water heater in a ready state to eliminate the cold water bursts that plague traditional tankless units. Combined with the 0.82 Uniform Energy Factor rating, this heater saves up to 34% on energy costs compared to 50-gallon electric tank heaters, delivering both comfort and substantial long-term savings on utility bills.
Build quality is solid with a stainless steel cabinet, durable metal construction, and an exclusive Overheat Film Wrap that protects the heat exchanger. The compact design measures just 13.5 inches wide and 20.75 inches tall, allowing installation in tight spaces where traditional tanks simply won't fit. The digital LED temperature control panel provides precision adjustments within plus/minus 1 degree Fahrenheit.
The main drawback is that professional installation is required and must be performed by a qualified installer, which adds to upfront costs. Additionally, while Hot Start Programming helps, some users report that a slight delay before hot water arrives is still noticeable, though this is inherent to tankless technology. The unit is designed for outdoor installation only, which may not suit all home configurations.
Overall, the Rheem RTG-84XLN-3 delivers reliable, efficient whole-house hot water with excellent warranties and proven customer satisfaction. It's a smart investment for homeowners seeking to eliminate hot water shortages while reducing energy consumption, backed by a robust 15-year heat exchanger warranty.
Model: RTG-84XLN-3
Power Source: Natural Gas
Flow Rate: 8.4 GPM at 35 degrees Fahrenheit temperature rise
Heat Output: 180,000 BTU per hour
Energy Factor: 0.82 UEF
Maximum Temperature: 140 degrees Fahrenheit
Electrical Requirements: 120 volts, 132 watts
Dimensions: 13.5 inches W x 20.75 inches H x 9.4 inches D
Weight: 39.3 pounds
Material: Stainless Steel with metal cabinet
Mount Type: Wall mount
Installation: Outdoor only, professional installation required
Warranty: 1 year labor, 15 years heat exchanger, 5 years parts
Who Should Buy This Unit? The Rheem RTG-84XLN-3 is ideal for large families, multi-bathroom homes, and properties with high hot water demand. If you currently experience running out of hot water during peak usage times or want to reduce energy bills, this tankless heater is a strong choice.
Installation Considerations: This unit requires professional installation by a qualified technician. Budget for installation costs in addition to the unit price. The outdoor-only design means you'll need adequate exterior wall space with proper venting clearance. The compact size helps with tight installations compared to traditional tank heaters.
Energy Savings: The 0.82 UEF rating delivers significant savings compared to standard 50-gallon electric tank heaters, potentially reducing energy costs by up to 34%. The on-demand heating technology means you only pay for hot water when you actually use it.
Performance Expectations: Expect continuous hot water for multiple simultaneous uses. The Hot Start Programming reduces but may not completely eliminate the initial cold water delay inherent to tankless units. Once hot water is running, the supply is essentially unlimited.
Long-Term Value: With a 15-year heat exchanger warranty and 5-year parts warranty, this unit is built for longevity. The stainless steel construction and overheat protection ensure reliable performance for many years of use.
Pros
- Delivers continuous hot water supply for multiple simultaneous uses without depletion
- Highly energy efficient with 0.82 UEF rating and minimal monthly gas consumption
- Compact footprint and wall-mount installation saves significant floor space
- Hot Start Programming keeps unit ready-state, eliminating annoying cold water delays
- Comprehensive safety features including freeze protection and flame failure detection
Cons
- Initial water temperature can take time to reach desired heat at the tap
- Requires professional installation for proper venting and gas line connections
- Needs periodic maintenance with vinegar flushing in hard water areas to prevent scaling
The Rheem RTG-70DVLN-3 is a high-performance natural gas tankless water heater designed for large families and multi-bathroom homes that demand continuous hot water without the bulk of traditional tank systems. This unit delivers 7.0 GPM flow rate at a 35 degree Fahrenheit temperature rise, supporting 2-3 simultaneous showers or water points with its 160,000 BTU output. It's an excellent replacement for aging tank water heaters, particularly for households tired of running out of hot water during peak usage times.
What sets this Rheem unit apart is its combination of efficiency and user-focused engineering. The exclusive Hot Start Programming keeps the heater in a ready state, virtually eliminating cold water bursts that plague some tankless systems between uses. The 0.82 Uniform Energy Factor means you'll see real savings on your gas bills, with users reporting increases of only $2-3 monthly compared to previous electric heaters. The integrated digital LED display offers precise temperature control with plus or minus 1 degree adjustments, giving you consistent water temperature exactly as you prefer it.
Build quality is solid throughout, with a stainless steel construction and wall-mount design that occupies minimal space compared to bulky tank heaters. The compact 13.5-inch width and 24.2-inch height fit into tight spaces while maintaining industry-leading installation clearance. The Overheat Film Wrap provides heat exchanger protection, and LeakGuard Leak Detection monitors for internal leaks both large and small, offering valuable peace of mind against potential water damage. The unit operates at just 132 watts and includes universal venting compatibility plus half-inch gas line compatibility for flexible installation options.
One honest drawback is that some users report a slight delay in reaching desired water temperature at the tap, particularly for the first use after a period of inactivity. This is inherent to how tankless systems work and can be partially mitigated by the Hot Start feature. In hard water areas, the unit requires biannual vinegar flushing to maintain optimal performance and prevent mineral scaling, adding a small maintenance requirement that tank heaters don't demand.
The Rheem RTG-70DVLN-3 is backed by an impressive warranty including 15 years on the heat exchanger and 5 years on parts, reflecting the manufacturer's confidence in durability. For households ready to eliminate hot water shortages and reduce energy consumption, this tankless system delivers reliable performance and genuine long-term value. It's particularly well-suited for families with multiple bathrooms or high simultaneous water demand.
Performance Metrics: Flow Rate: 7.0 GPM at 35 degree Fahrenheit temperature rise. Heat Output: 160,000 BTU/hr. Maximum Temperature: 140 degrees Fahrenheit. Energy Factor: 0.82 UEF (saves up to 34% vs. 50-gallon electric tanks).
Physical Specifications: Dimensions: 13.5 inches width by 24.2 inches height by 10.27 inches depth. Weight: 46.5 pounds. Mount Type: Wall. Material: Stainless Steel. Color: Gray.
Electrical and Fuel: Power Source: Natural Gas. Wattage: 132 watts. Voltage: 120 volts. Gas Line Compatibility: 1/2 inch. Venting: Universal compatibility with direct vent system.
Features: Integrated Digital LED Display. Hot Start Programming. High Energy Efficiency. Integrated Leak Detection and Prevention. Freeze Protection. Flame Failure Protection. Temperature Control: Plus or minus 1 degree precision adjustment.
Warranty: 1 Year Labor. 15 Years Heat Exchanger. 5 Years Parts.
Who Should Buy This Unit: The Rheem RTG-70DVLN-3 is ideal for families of 3 or more living in homes with multiple bathrooms or high simultaneous water demand. It's perfect for households currently using electric tank heaters who want to reduce energy consumption and eliminate hot water shortages. The compact design makes it suitable for apartments, condos, and homes with limited utility space.
Installation Considerations: This is not a DIY-friendly product for most homeowners. Professional installation is strongly recommended to ensure proper gas line connections, venting configuration, and local code compliance. Budget for professional installation costs in addition to the unit price. Confirm your home has natural gas service and adequate venting options before purchasing.
Maintenance Requirements: In areas with hard water, plan to flush the unit with distilled white vinegar twice yearly to prevent mineral buildup and maintain efficiency. This is a simple process but requires commitment. Soft water areas may need flushing less frequently. Regular inspection of the LeakGuard system is recommended as part of routine home maintenance.
Comparison Context: Compared to traditional tank heaters, this unit costs more upfront but delivers lower operating costs, unlimited hot water supply, and space savings. Compared to other tankless systems, Rheem's reputation for reliability and the Hot Start feature that eliminates cold water delays make this a strong value choice. The 15-year heat exchanger warranty is longer than many competitors offer.
Our Best Gas Hot Water Picks Reviewed
The Rheem RTG-84XLN-3 (8.4 GPM) and the Rheem RTG-70DVLN-3 (7.0 GPM) suit different buyers, and the comparison below shows where each one wins.
- Rheem RTG-84XLN-3 (8.4 GPM): This model delivers up to 8.4 gallons per minute with a 180,000 BTU output. It is ideal for larger homes with several bathrooms and high hot water demand.
- Rheem RTG-70DVLN-3 (7.0 GPM): This model supports two to three simultaneous showers with a compact wall-mount design and a 0.82 UEF efficiency rating. It suits most medium-size households.
How to Size a Gas Hot Water Heater
Estimate peak demand by adding the flow rates of fixtures you use at the same time:
- Shower: about 2 GPM.
- Kitchen faucet: about 1.5 GPM.
- Dishwasher: about 1 to 1.5 GPM.
- Washing machine: about 1.5 to 2 GPM.
If your peak demand is around 6 GPM, the 7.0 GPM model is a good fit. If it is higher, or if you live in a cold climate with very cold incoming water, the 8.4 GPM model provides more headroom.
How to Choose the Best Gas Hot Water Heater
The right choice comes down to flow rate, BTU input, efficiency, and venting and gas line.
- Flow Rate: Choose a unit that meets your peak demand with some extra capacity.
- BTU Input: Higher BTU input supports higher flow rates and colder incoming water.
- Efficiency: Higher UEF ratings mean lower gas use.
- Venting and Gas Line: Tankless gas hot water units require proper venting and an adequate gas supply.
- Installation Space: Wall-mounted units free up floor space compared with tank heaters.
Maintenance Tips
- Flush the system annually to prevent scale buildup.
- Clean the inlet filter regularly.
- Keep vents clear of debris.
- Schedule professional service as recommended.
For more options, read our guides to the best gas hot water heater review and the best tankless hot water picks.
Comparing the Two Models
The Rheem RTG-84XLN-3 is rated up to 8.4 gallons per minute and suits larger households with several bathrooms. It is designed for outdoor installation, which saves indoor space. The Rheem RTG-70DVLN-3 is rated up to 7.0 gallons per minute and uses direct venting for indoor installation.
Choosing Indoor or Outdoor
Outdoor models avoid indoor venting but need a mild climate or freeze protection. Indoor models need proper venting but stay protected from the weather.
Permits and Professional Installation
Gas water heaters need a correctly sized gas line, approved venting, and often a permit and inspection. A licensed plumber or gas fitter should handle installation. Install a carbon monoxide detector near any gas appliance.
Common Mistakes to Avoid
Do not install an outdoor model where freezing is common without protection. Avoid undersized gas lines, and size by peak demand when choosing gas hot water equipment.
Final Verdict on the Best Gas Hot Water
Among the best gas hot water heaters from Rheem, the RTG-84XLN-3 is the best choice for large households, thanks to its 8.4 GPM flow and 180,000 BTU output. For medium-size homes, the RTG-70DVLN-3 offers 7.0 GPM, a compact design, and a 0.82 UEF rating.
Gas Hot Water FAQs
Common questions from buyers include “What size tankless gas heater do I need?”, “Does climate affect performance?”, and “Are tankless gas heaters efficient?”.
What size tankless gas heater do I need?
Add the flow rates of fixtures used at the same time, and choose a unit that exceeds that number.
Does climate affect performance?
Yes. Colder incoming water reduces the flow rate a unit can heat.
Are tankless gas heaters efficient?
Yes. They avoid standby heat loss and often have high UEF ratings.
Do I need a bigger gas line?
Tankless units often need a larger gas supply than tank heaters. Check with a professional.
How often should I flush a tankless heater?
About once a year, or more often in hard water areas.
For more home gear, browse our best water heaters category.
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