Replacing a bulky 50-gallon storage tank with a gas-fired tankless water heater is one of the most impactful upgrades you can make to your home’s energy efficiency and daily comfort. The promise of endless hot water without the standby heat loss of a traditional tank is compelling, but choosing the right unit for your home’s specific flow demands, gas supply, and installation location requires careful consideration of BTU output, gallon-per-minute ratings, and the real-world temperature rise in your region.
I’m Mohammad Maruf — the founder and writer behind Drink4Good. I’ve spent years analyzing tankless water heater specifications, comparing copper versus stainless steel heat exchangers, and evaluating the trade-offs between condensing and non-condensing designs to help homeowners make informed, lasting decisions.
Finding the right model can be overwhelming, which is why this guide breaks down the top contenders, matching each to a specific household need so you can confidently choose the best 50 gallon gas water heater replacement or tankless alternative for your home.
How To Choose The Best Tankless Gas Water Heater
Selecting a tankless water heater isn’t just about picking the highest BTU rating. You need to match the unit’s flow rate — measured in gallons per minute (GPM) — to your household’s simultaneous fixture usage, accounting for your incoming groundwater temperature. A unit that works perfectly in Florida may struggle to deliver enough hot water during a Minnesota winter.
Calculate Your Required GPM
Add up the flow rates of all fixtures you might use at once. A typical shower uses 1.5–2.5 GPM, a kitchen faucet 1.0–1.5 GPM, and a washing machine 1.5–2.0 GPM. A 4–5 GPM unit can handle two showers and a sink, while a 7–9 GPM unit supports three bathrooms plus appliances. Undersizing leads to disappointing temperature drops.
BTU Output and Temperature Rise
BTU (British Thermal Unit) measures the heater’s power. Higher BTU ratings allow the unit to raise water temperature by more degrees — critical in cold climates where ground water can be 40–50°F. The required temperature rise is your desired output temperature (usually 120°F) minus your incoming water temperature. A higher BTU unit will maintain flow rate through a larger rise.
Condensing vs. Non-Condensing
Non-condensing units are simpler and less expensive upfront but require dedicated stainless steel venting and lose some efficiency through exhaust heat. Condensing models capture that exhaust heat for higher UEF ratings (often above 0.95) and can use standard PVC venting, but they cost more initially and require a condensate drain line. For colder climates, the energy savings of a condensing model can offset the higher purchase price over time.
Quick Comparison
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| Model | Category | Best For | Key Spec | Amazon |
|---|---|---|---|---|
| Rinnai RX199iN | Premium Condensing | Large families, 7+ fixtures | 11.1 GPM, UEF 0.98 | Amazon |
| Rheem RTG-95DVLN-3 | High-Capacity Non-Condensing | High simultaneous demand | 9.5 GPM, 199,900 BTU | Amazon |
| Rinnai RX130iN | Mid-Size Condensing | Versatile indoor/outdoor install | 7.1 GPM, UEF 0.97 | Amazon |
| Westinghouse 7.9 GPM Indoor | Smart Non-Condensing | WiFi control & stable temps | 7.9 GPM, 180,000 BTU | Amazon |
| Westinghouse 8.1 GPM Outdoor | Outdoor Smart Unit | Outdoor installations | 8.1 GPM, 180,000 BTU | Amazon |
| Rheem RTG-70DVLN-3 | Mid-Range Non-Condensing | 2-3 bathroom homes | 7.0 GPM, 160,000 BTU | Amazon |
| Noritz NR50ODNG | Compact Outdoor | Smaller homes, outdoor install | 5.0 GPM, 120,000 BTU | Amazon |
| APUS 190,000 BTU Outdoor | High-Flow Outdoor | Whole-home outdoor demand | 8.1 GPM, 190,000 BTU | Amazon |
| GASLAND Gasmart E | High-BTU Non-Condensing | High BTU, budget-conscious | 7.6 GPM, 199,000 BTU | Amazon |
| MIZUDO Natural Gas | Indoor/Outdoor Convertible | Flexible placement options | 5.1 GPM, 120,000 BTU | Amazon |
| APUS Propane Tankless | Propane with Recirc Pump | Propane homes, instant hot water | 6.8 GPM, 140,000 BTU | Amazon |
In‑Depth Reviews
1. Rinnai RX199iN Condensing Smart Sense
The Rinnai RX199iN is the highest-flow unit in this comparison, delivering up to 11.1 GPM — enough to run seven fixtures simultaneously without a noticeable pressure drop. Its condensing design with a UEF rating of 0.98 means it captures nearly all the heat from combustion, making it one of the most efficient residential gas water heaters available. The Smart Sense gas control system automatically detects whether you’re supplying natural gas or propane, eliminating the need for a conversion kit.
Installation is versatile thanks to Rinnai’s Versa Vent system, which allows indoor or outdoor placement using the same unit. The RX199iN also includes a Quick Flush feature that simplifies periodic descaling. Owners report reliable performance in homes with three or more bathrooms and high-demand appliances, with many noting the substantial reduction in fuel costs compared to a traditional 50-gallon tank.
This unit does require a dedicated 120V electrical outlet and professional installation is recommended for ensuring proper gas line sizing and venting. The 5-year parts and labor warranty provides solid long-term coverage, and the optional Controlr module adds WiFi control for remote temperature adjustments.
Why it’s great
- Industry-leading 11.1 GPM flow supports large families with multiple bathrooms
- UEF 0.98 efficiency delivers maximum energy savings and qualifies for potential rebates
- Versa Vent allows flexible indoor or outdoor installation with the same unit
Good to know
- Higher upfront cost than non-condensing models
- Requires a condensate drain line and 120V electrical supply
2. Rheem RTG-95DVLN-3 Non-Condensing
With a massive 199,900 BTU input and 9.5 GPM flow rating, the Rheem RTG-95DVLN-3 is built for homes that demand serious hot water output. This non-condensing indoor unit is designed for 2–3 bathroom households running simultaneous showers, laundry, and dishwashing. Rheem’s Hot-Start programming minimizes the cold water burst between uses, so back-to-back showers stay consistent.
The compact metal cabinet measures just 13.5 inches wide, saving floor space compared to a tank system. It requires standard 3/4-inch NPT water connections and a dedicated stainless steel venting system (not included). Owners appreciate the simple LED display and straightforward temperature adjustment, though some note the internal fan can be audible from adjacent rooms if not well-isolated.
One trade-off with non-condensing design is a slightly lower UEF rating — this unit sits around 0.82 — meaning some heat is lost through the exhaust. However, for homeowners in moderate climates who don’t need the highest possible efficiency, the lower purchase price and simpler installation without a condensate line make it an attractive value.
Why it’s great
- High 9.5 GPM flow and 199,900 BTU handle peak household demand easily
- Compact 13.5-inch width frees up valuable floor space
- Hot-Start programming reduces cold water bursts between consecutive uses
Good to know
- UEF 0.82 means less energy efficiency compared to condensing models
- Requires professional installation with dedicated stainless steel venting
3. Rinnai RX130iN Condensing Smart Sense
The Rinnai RX130iN offers the same innovative Smart Sense gas control and Versa Vent compatibility as its larger sibling but with a 7.1 GPM flow rate — ideal for homes with up to four fixtures running simultaneously. Its condensing design achieves a UEF of 0.97, placing it among the most efficient mid-capacity tankless water heaters on the market.
One standout feature is the ability to install the same unit indoors or outdoors, using PVC venting indoors with the Versa Vent system or a simple vent cap for outdoor mounting. This flexibility is valuable for homeowners with limited interior space or those converting a utility closet. The 5-year labor and parts warranty provides solid protection for a purchase that requires professional hookup.
Users report excellent performance in cold climates, with one owner in alpine conditions noting it maintained two showers and a dishwasher simultaneously with outdoor temperatures around 10°F. The propane/natural gas autodetection eliminates guesswork. The only common complaint is that the flush valves and pressure relief valve are sold separately, adding around to the initial setup.
Why it’s great
- UEF 0.97 efficiency delivers near-maximum energy recovery
- Versa Vent allows indoor or outdoor installation with minimal parts
- Automatic gas type detection supports natural gas or propane
Good to know
- Flush valves and pressure relief valve must be purchased separately
- Optional WiFi module adds cost but enables app control
4. Westinghouse Smart Tankless 7.9 GPM Indoor
Westinghouse brings smart home integration to the tankless water heater category with this 180,000 BTU indoor unit that delivers 7.9 GPM. The built-in WiFi capability allows you to adjust the output temperature and monitor system status directly from your smartphone, which is convenient for preheating before a shower or checking diagnostics remotely.
Advanced self-modulating technology maintains water temperature within ±1°F, which effectively eliminates the cold bursts that can occur when another fixture turns on. The non-condensing design keeps the purchase price accessible, and the compact wall-mounted profile fits neatly into a utility room or garage. CSA certification and integrated freeze protection make it suitable for installations in unheated indoor spaces.
Owners consistently mention the straightforward installation process, with several DIY users reporting successful swaps in under three hours using the included step-by-step instructions. The unit requires standard 3/4-inch NPT connections and a dedicated 120V outlet. One trade-off is that the residential warranty details should be verified before purchase — some users found the registration process necessary for full coverage.
Why it’s great
- WiFi app control for remote temperature adjustment and monitoring
- ±1°F temperature stability prevents cold water bursts
- Compact design with straightforward DIY-friendly installation
Good to know
- Non-condensing design loses some efficiency through exhaust
- Warranty registration may require submission of proof of purchase
5. Westinghouse Smart Tankless 8.1 GPM Outdoor
This outdoor version of Westinghouse’s smart tankless heater shares the same 180,000 BTU power and ±1°F temperature control as the indoor model, but adds weather-resistant construction designed for exterior wall mounting. At 8.1 GPM, it can comfortably support 3–5 fixtures, making it a strong option for homes where indoor space is at a premium.
The outdoor design eliminates the need for venting through the roof or wall, which can significantly reduce installation complexity and cost. It includes a wired control panel for on-unit adjustments and supports WiFi connectivity through the same smartphone app. Integrated freeze protection and a variable-speed combustion fan ensure reliable operation even when temperatures drop.
Users praise the quiet fan operation — one owner described it as barely audible from inside the house. The unit requires 3/4-inch NPT water and gas connections and a 120V AC power source. It works well for vacation properties and cabins where year-round outdoor durability is essential, though some owners recommend adding heat tape and foam insulation for extreme northern climates.
Why it’s great
- Outdoor installation saves indoor space and eliminates venting costs
- 8.1 GPM supports multiple simultaneous fixtures
- Quiet operation with weather-resistant construction
Good to know
- Requires exterior wall space and a 120V outlet
- Additional weatherproofing may be needed in extreme cold climates
6. Rheem RTG-70DVLN-3 Non-Condensing
The Rheem RTG-70DVLN-3 sits at a sweet spot for 2–3 bathroom homes, delivering 7.0 GPM and 160,000 BTU. It’s a non-condensing indoor unit that offers reliable performance without the higher price tag of condensing technology. The Hot-Start programming is particularly useful for families who take consecutive showers in the morning.
Installation requires dedicated stainless steel venting and a 120V power source. The unit includes an altitude adjustment setting, which is essential for homes above 2,000 feet to ensure proper combustion. Owners report good performance even with older, undersized copper piping — the internal flow regulation compensates for lower line pressures.
The 15-year heat exchanger warranty is noteworthy for a non-condensing unit at this price tier, signaling Rheem’s confidence in the oxygen-free copper heat exchanger’s durability. Some users note that the venting pipe is a specialized requirement that can be harder to source locally, so planning ahead for materials is recommended.
Why it’s great
- 15-year heat exchanger warranty provides long-term peace of mind
- 7.0 GPM meets the needs of most 2–3 bathroom households
- Altitude adjustment ensures proper combustion at higher elevations
Good to know
- Requires specialized stainless steel venting pipe
- Non-condensing design sacrifices some efficiency for lower initial cost
7. Noritz NR50ODNG Outdoor
The Noritz NR50ODNG is a proven, no-frills outdoor unit that prioritizes reliability and simplicity. With a 5.0 GPM flow rate and 120,000 BTU output, it’s best suited for smaller homes, apartments, or as a dedicated unit for specific zones. Its outdoor installation eliminates venting concerns entirely — just mount it on an exterior wall and connect gas and water lines.
One of the most appealing aspects of this model is its energy efficiency in real-world use. Long-term owners report natural gas bills dropping by roughly 50% compared to their old 50-gallon tank systems. The compact 33-pound weight makes it one of the easiest units to mount during installation. Noritz is a brand frequently recommended by professional plumbers for its parts availability and straightforward design.
The minimum operating temperature is 115°F, which is warmer than some competitors that go down to 99°F. For warm climates where you prefer cooler shower temperatures, this could mean less gas savings. The optional remote controller must be purchased separately and restricts temperature range after initial setup from 140°F down to 115–120°F.
Why it’s great
- Outdoor installation eliminates venting complexity and cost
- Lightweight 33-pound design is easy to handle during setup
- Proven reliability with broad parts availability at local supply houses
Good to know
- Minimum outlet temperature of 115°F is not ideal for warmer climates
- Remote controller sold separately and may limit temperature range
8. APUS 190,000 BTU Outdoor Natural Gas
APUS brings an impressive combination of high flow and smart features to this outdoor unit. With 190,000 BTU output and 8.1 GPM, it can handle three showers plus two faucets simultaneously — making it one of the most capable outdoor tankless units in this comparison. The ultra-low 0.79 GPM minimum activation flow is a standout, allowing the heater to fire even in homes with weak water pressure.
Smart temperature control works through the Tuya app or a wired controller, giving you ±1°F precision from 95°F to 149°F. The 100% oxygen-free copper heat exchanger uses intelligent staged combustion to boost energy savings by up to 20% compared to standard non-condensing units. Outdoor durability is addressed with a 10-level wind resistance rating and electric anti-freeze protection.
The unit is relatively compact at 22.48 × 15.51 × 6.54 inches, and the standard 3/4-inch NPT water and gas connections simplify integration with most home systems. Owners especially appreciate the quiet operation — one user noted it’s quieter than their previous tank heater. The 2-year full warranty covers all components, though outdoor installations in extreme climates may benefit from additional insulation on exposed pipes.
Why it’s great
- 8.1 GPM and 190,000 BTU handle three showers plus two faucets
- Ultra-low 0.79 GPM minimum activation works with weak water pressure
- 10-level wind resistance and anti-freeze protection for outdoor durability
Good to know
- Requires a separate valve body for installation in some configurations
- WiFi control via Tuya app may require a reliable network connection
9. GASLAND Gasmart E 199,000 BTU Natural Gas
The GASLAND Gasmart E packs 199,000 BTU into a surprisingly compact package, delivering 7.6 GPM for whole-house coverage. It’s a non-condensing indoor unit rated with a UEF of 0.8, which is 34% more efficient than a standard 50-gallon tank heater. The CSA certification covers safety standards and includes overheat, flame-out, and freeze protection.
Installation requires a 3-inch venting system (sold separately) and professional gas line hookup. The unit uses an oxygen-free copper heat exchanger and an iron outer body. Customer support is based in the US, and the manufacturer offers a 1-year replacement policy if the unit fails. The included mounting kit and adapter simplify wall installation.
Owners report good performance for families of four, with ample hot water for a large garden tub plus daily showers. One common installation challenge is the uneven inlet and outlet spacing, which can complicate line connections — careful measurement before cutting pipes is advised. The unit is not Energy Star certified, so it may not qualify for local utility rebates.
Why it’s great
- High 199,000 BTU output for demanding simultaneous usage
- 34% more efficient than a standard 50-gallon tank water heater
- US-based customer support with a 1-year replacement policy
Good to know
- Uneven inlet/outlet spacing may complicate connection setup
- Not Energy Star certified, so rebates may not be available
10. MIZUDO Natural Gas Tankless (Indoor/Outdoor)
The MIZUDO natural gas tankless offers unique flexibility by allowing both indoor and outdoor installation with the same base unit, using an optional conversion kit. At 5.1 GPM and 120,000 BTU, it’s aimed at smaller households or as a dedicated unit for specific zones. The WiFi and app control via a dedicated mobile application allow remote temperature adjustment and usage monitoring.
Advanced temperature control maintains stability within ±1°F, preventing sudden temperature swings when multiple fixtures are in use. The phosphorous-deoxidized copper heat exchanger and stainless steel combustion chamber are built for longevity. CSA certification covers safety features including freeze protection, dry burn prevention, flame failure detection, and exhaust blockage protection.
Indoor installation requires a 3-inch OD vent pipe system (sold separately), while outdoor installation needs a specific vent cap conversion kit. Owners report straightforward installation with fast heating response, though some note that the included gas fitting is not a standard 1/2-inch MIP and requires an adapter. The 2-year full unit warranty and 5-year heat exchanger coverage provide solid protection.
Why it’s great
- Convertible for indoor or outdoor installation with additional accessory kit
- WiFi app control and ±1°F temperature precision
- Phosphorous-deoxidized copper heat exchanger for durability
Good to know
- Gas fitting is not a standard 1/2-inch MIP — adapter required
- Vent pipe or outdoor conversion kit must be purchased separately
11. APUS Tankless Water Heater Propane 140,000 BTU
This APUS propane tankless heater is an excellent choice for homes without natural gas access. Running on liquid propane, it delivers 140,000 BTU and up to 6.8 GPM — enough for two showers and two sinks simultaneously. The standout feature is the built-in recirculation pump that the manufacturer calls “Zero Cold Water Tech,” eliminating the cold water wait that typically plagues tankless systems.
The unit includes WiFi control via the Tuya app, allowing remote temperature adjustment from 95°F to 140°F and system monitoring. A built-in booster pump can increase flow by up to 130%, ensuring adequate water pressure even in homes with low incoming pressure. The smart season comfort mode automatically adjusts outlet temperature based on incoming water temperature, keeping output consistent year-round.
Indoor installation requires proper venting — the unit ships with a single-wall 2 3/8-inch exhaust pipe that may be smaller than some existing venting systems, so check compatibility before installation. Owners report excellent hot water delivery with the recirculation feature, but note that customer service responsiveness is variable. The 24/7 US support team is available, but some buyers have experienced ignition issues that required professional attention.
Why it’s great
- Built-in recirculation pump provides instant hot water, eliminating wait time
- WiFi control with Tuya app for remote operation and monitoring
- Booster pump enhances flow up to 130% for low-pressure homes
Good to know
- Exhaust pipe size may differ from existing venting — check compatibility
- Customer service responsiveness has received mixed feedback
FAQ
Can a tankless gas water heater replace my existing 50-gallon tank?
How do I know if I need a condensing or non-condensing tankless heater?
Why does my tankless water heater take longer to deliver hot water than my old tank?
Final Thoughts: The Verdict
For most users replacing a 50 gallon gas water heater with a tankless system, the winner is the Rinnai RX199iN because its 11.1 GPM flow and UEF 0.98 efficiency cover the largest households while maximizing energy savings. If you want a smart-enabled unit with intuitive WiFi control and ±1°F stability, grab the Westinghouse 7.9 GPM Indoor. And for outdoor installations where venting simplicity and weather resistance matter most, nothing beats the Westinghouse 8.1 GPM Outdoor.