Reader support keeps this site open, opinionated, and happily independent. As an Amazon Associate, I earn from qualifying purchases.11 Best 40 Gallon Gas Water Heater | Gas vs Propane Showdown

Check Price on Amazon

The FOGATTI 180S is the powerhouse of this lineup, delivering 180,000 BTU with a maximum flow rate of 8.1 GPM. That capacity comfortably handles three to five simultaneous outlets—think two showers, a dishwasher, and a washing machine running at the same time without a noticeable temperature dip. The four-stage combustion system paired with water servo technology keeps output within a tight temperature range, which matters when you have a teenager taking a 20-minute shower while someone else starts the laundry.

Installation is outdoor-only, which sidesteps the venting cost and complexity of indoor units. The bottom-mounted fan design prevents smoke backflow and improves combustion stability in windy conditions. It works with water pressures as low as 15 PSI, making it viable for well-water systems. The oxygen-free copper heat exchanger and 304 stainless steel burner are built for corrosion resistance, a key factor for outdoor exposure.

Customer feedback highlights instant ignition and consistent temperatures across multiple fixtures. The remote control panel mounts inside the home for convenient temperature adjustment without braving the elements. The 2-year full unit warranty and 5-year heat exchanger coverage provide decent protection, though some users noted difficulty reaching technical support for troubleshooting.

Check Price on Amazon

The CAMPLUX CA528 is an indoor-rated gas tankless water heater that delivers up to 6.4 GPM with a 150,000 BTU burner. It’s designed for whole-house applications with three to five family members, supporting up to three bathrooms and two kitchens simultaneously. The unit uses an oxygen-free copper heat exchanger with a claimed 96.9% efficiency, which translates to better heat extraction from the same gas input compared to stainless steel exchangers.

At 23.43 x 14.92 x 6.69 inches and just over 31 pounds, this unit is compact enough to mount on a wall in a utility closet or basement. It connects to existing 3/4-inch gas and water lines. The self-diagnostic system monitors for mineral buildup, which can extend the lifespan beyond a decade if your water hardness is managed. The six-point safety system includes freeze protection, dry-fire prevention, and flame failure detection with a response time faster than UL standards.

Real-world owner feedback confirms it replaces a 40-gallon tank heater with a noticeable drop in gas bills—some users reported their bill halved. The main trade-off is that the unit requires power to operate (no hot water during a blackout), and the indoor installation requires a 3-inch Category III vent system that can add significant cost if not already in place.

Check Price on Amazon

The propane version of the CAMPLUX Climatech 5 delivers identical 150,000 BTU output and up to 6.4 GPM but is designed for outdoor installation only. This makes it a strong choice for homes without indoor mechanical room space or where running a vent stack would be cost-prohibitive. The unit connects to standard 3/4-inch NPT water fittings and does not require venting, which simplifies the install significantly.

The burner uses a three-speed automatic flame adjustment system paired with a high-precision gas proportional valve. The result is consistent output within a tight temperature range even when multiple fixtures are opened. The CSA certification covers freeze protection, dry-fire prevention, and flame failure detection. The unit also includes a wired remote control that can be mounted indoors for convenient temperature adjustment.

Buyers report that this unit handles the hot water needs of a typical three-bedroom home without issue. Some noted that it works well with low water pressure (as low as 24 PSI in one user’s off-grid setup). The 31.3-pound weight makes wall mounting a one-person job. One caveat: propane units require a dedicated propane tank or connection, and performance drops at altitudes above 2,000 feet unless adjusted.

Check Price on Amazon

The MIZUDO GEN 3 is the only unit in this roundup that offers WiFi and app-based remote control, letting you adjust temperature or monitor energy usage from your phone. It delivers 120,000 BTU with a 5.1 GPM flow rate, which is adequate for a two-bathroom household but may struggle if you’re running three showers at once. What sets this model apart is its convertible installation—it ships ready for outdoor use, and a separate vent kit allows indoor installation.

The phosphorous-deoxidized copper heat exchanger offers better corrosion resistance than standard copper, and the stainless steel combustion chamber adds durability. The unit maintains output within a tight temperature window thanks to a combination of water flow monitoring and gas modulation. Safety features include freeze protection, dry burn prevention, flame failure detection, and exhaust blockage protection. CSA certification confirms compliance with US standards.

Owners in the field report that the WiFi app works reliably for temperature adjustments and that the unit is noticeably quieter than older tankless models. The 2-year full unit warranty and 5-year heat exchanger coverage are standard for this tier. The main downside is that the 5.1 GPM ceiling means it’s better suited for smaller homes—a large family running heavy simultaneous demand may see performance limitations.

Check Price on Amazon

Rinnai is one of the most recognized names in tankless water heating, and the V53DeP lives up to that reputation. It delivers 5.3 GPM with a rated heat output of 81 kW, roughly equivalent to 276,000 BTU—though that figure is expressed in kilowatts in the specifications. The unit is designed for outdoor installation only, which keeps the setup straightforward and eliminates the need for a vent stack. It’s compact at 13 x 30 inches and weighs 33 pounds.

The real draw here is the warranty: a 10-year heat exchanger warranty, a 5-year labor warranty, and a 1-year parts warranty. That coverage reflects Rinnai’s confidence in the build quality and is significantly longer than most competitors. The unit includes improved scale detection to enhance lifespan in hard water areas. It connects to standard propane cylinders and can handle up to three fixtures at 115°F based on user reports.

Field feedback highlights reliable performance even in cold weather—one user reported flawless operation at 5°F ambient temperature. Another noted that it uses less propane than a previous unit for the same hot water output. The downsides: the V53DeP does not include a temperature controller out of the box (requires a separate purchase or dip switch adjustment), and the electrical connection requires a hardwired switch rather than a plug.

Check Price on Amazon

The FOGATTI 120S is the smaller sibling of the 180S, delivering 120,000 BTU with a 5.1 GPM flow rate. This is a solid fit for a medium-sized family—two to three people running a shower, a kitchen sink, and a dishwasher simultaneously. The unit uses a four-stage combustion system and water servo technology to maintain a tight temperature window, which means you won’t feel sudden cold bursts when someone turns on a faucet in another room.

Outdoor installation keeps the job simple: mount it on an exterior wall, connect 3/4-inch NPT water lines and a 120V power source, and you’re in business. The unit handles low water pressure down to 15 PSI, which is unusual for tankless units and a big plus for homes on well water or with aging plumbing. The 304 stainless steel burner and oxygen-free copper heat exchanger are built for outdoor durability.

Buyers report easy installation and immediate performance. One owner noted they would buy it for their house after using it in an RV. The active anti-freeze feature protects down to 5°F, but the manufacturer recommends draining the unit if temps drop below that or if it won’t be used for an extended period. The 2-year full warranty and 5-year heat exchanger coverage are standard; some users reported difficulty contacting customer support.

Check Price on Amazon

The Ranein propane unit splits the difference between the 120,000 BTU and 150,000 BTU tiers with a 130,000 BTU output and a maximum flow rate of 5.3 GPM. It’s designed for homes with three to five water outlets and provides enough capacity for a family of four running two showers and a dishwasher. The bottom-mounted fan design is a thoughtful safety feature—it prevents smoke backflow and reduces noise compared to top-mounted fan units.

The unit uses standard 1/2-inch NPT water inlet fittings (smaller than the 3/4-inch standard on most competitors) and a 3/4-inch gas line connection. It’s compact at 23.2 x 14.2 x 5.7 inches and weighs 34 pounds. Safety features include anti-freeze protection, dry burn prevention, and overheat protection. The maximum temperature is 155°F, which is higher than many competitors that max out at 149°F.

User reports highlight significant propane savings—one owner estimated a reduction in usage of about per month compared to their old tank heater. Another noted that a 30-pound propane tank lasted three months with daily showers and dishes. The 2-year manufacturer warranty is standard. Some users experienced part failures within the first year, though customer service replaced the entire unit in those cases.

Check Price on Amazon

The MIZUDO Gen 2 is a no-frills propane tankless water heater offering 120,000 BTU and 5.1 GPM for outdoor installation. It’s designed for homes with two to three bathrooms and provides enough hot water for a family of four running one to two showers at a time. The unit uses a gas proportional valve and water volume servo to maintain its temperature output, with the manufacturer claiming a tight temperature window.

At 23.94 x 15.51 x 7.28 inches, it takes up minimal wall space outdoors. The unit requires 120V power and 3/4-inch NPT connectors. The CSA certification covers freeze protection, dry burn prevention, flame failure detection, and exhaust blockage protection. The active anti-freeze feature helps prevent damage during cold snaps, though the manufacturer recommends draining the unit if it won’t be used for extended periods in freezing weather.

Buyers report that it performs well for its price point, with one RV owner noting a 5-gallon propane tank lasting 2-3 weeks with two 10-minute showers daily. Another user replaced a dead heater in a cabin and found the digital display and silent operation to be major upgrades. The main limitations are the 5.1 GPM ceiling and the outdoor-only installation requirement. Some owners found the freeze protection inadequate in very cold basements.

Check Price on Amazon

The ORBEK natural gas tankless water heater is the most budget-friendly option in this lineup, delivering 120,000 BTU with a 5.1 GPM flow rate. It’s designed for outdoor installation only and connects via 3/4-inch NPT fittings. The unit features a low-flow start technology that activates at just 0.53 GPM, which means it can kick on even with a small demand like a single bathroom sink—something some budget units struggle with.

The oxygen-free copper heat exchanger heats water quickly, and the built-in chip adjusts the temperature 20,000 times per second to keep output stable. The operating range is 95°F to 149°F, and the unit remembers your setting after a power outage. CSA certification covers anti-dry burning, anti-overheating, anti-leakage, anti-flameout, and high water pressure protection.

User reviews are mixed. Several buyers praise the unit for turning on with minimal flow and delivering constant hot water for long showers. But a significant number of negative reviews report units failing within the first 90 days with error codes related to exhaust blockage, and customer support either unresponsive or redirecting to Amazon. At this price point, the gamble is real—unit reliability and support appear inconsistent.

Check Price on Amazon

The Dometic WH-10GEA is a completely different animal from the rest of this list—it’s a 10-gallon tank-style water heater designed specifically for RVs and campers. It runs on either propane gas (10,000 BTU burner) or 12V electric, making it versatile for boondocking or hookups. The lightweight aluminum tank requires no anode rod, reducing maintenance, and the pre-installed winterization bypass kit simplifies cold-weather storage.

At 17.25 x 16.75 inches and only 22 pounds, this unit is significantly smaller and lighter than any residential tankless option. The electronic ignition eliminates the need for a standing pilot light, saving propane when not in use. It’s a direct replacement for many Atwood 10-gallon models, making it a straightforward swap for RV owners upgrading a failed unit.

Owner reports confirm a simple installation process, with one user noting it was a direct fit for a 23-year-old Atwood unit. The main drawback is poor insulation—several owners reported the cabinet area getting 15°F warmer, indicating heat loss through the tank walls. The 2-year limited warranty is short compared to residential units, but standard for RV appliances.

Check Price on Amazon

The Ecosmart ECO 36 is an electric tankless water heater, included here as an alternative for homes that don’t have natural gas or propane access. It delivers up to 6 GPM with 36 kW of heating power and operates at 99.8% energy efficiency. The unit is compact at 21 x 17 inches and weighs only 18.4 pounds, making it one of the lightest options in this guide.

The catch—and it’s a big one—is the electrical requirement. The ECO 36 needs four 40-amp double-pole breakers, which means it occupies eight slots in your breaker panel. Many older homes lack the service capacity to add this load without a costly panel upgrade. It uses 3/4-inch NPT connections and features a digital temperature display.

Owner feedback is mostly positive, with many reporting flawless performance for 3-4 years and counting. Users note that it handles one shower easily even in Ohio winters, but may struggle with two simultaneous showers when the incoming water temperature is very cold. The limited lifetime warranty is a strong selling point, but it requires registration within 30 days of purchase. Some owners reported motherboard failures and difficulty with warranty claims when registration was missed.