With so many great Best 40 Gallon Natural Gas Water Heater to pick from, like those from brands such as Ranein,thermomate,FOGATTI,NOVIEEX, it can be tricky for customers to decide what to buy. But after extensive research, we’ve discovered the stand-out Best 40 Gallon Natural Gas Water Heater currently on the market.
Our team rigorously tested numerous products available to consumers. The one that stands at the top of our list is Ranein Best 40 Gallon Natural Gas Water Heater, thanks to its impressive performance and features. Below you’ll find more of our top-rated picks, along with insightful analysis from our seasoned experts. Check out their thoughts before making your purchasing choice. With this guide backing your decision, you’re sure to end up with a Best 40 Gallon Natural Gas Water Heater you’ll love.
Editor's Choice
Ranein Natural Gas Tankless Water Heater with Vent Pipe, Indoor Max 4.3 GPM, 100,000 BTU Instant Hot
Premium Pick
2025 GEN II Ranein Natural Gas Tankless Water Heater Max 3.6 GPM, 80,000 BTU Indoor On Demand
Budget Pick
ThermoMate CZ422NG Natural Gas Tankless Water Heater, Up to 5 GPM 113,000 BTU, High Efficiency
Top 10 Best 40 Gallon Natural Gas Water Heater
We researched and compared the top products in the Best 40 Gallon Natural Gas Water Heater category to provide you with these recommendations.
1. Ranein Natural Gas Tankless Water Heater, Indoor Max 3.6 GPM, 80,000 BTU Instant Hot Water Heater
- Performance: The on-demand tankless water heater boasts a heating capacity of 80,000 BTU and a hot water flow rate of 3.6 gallons per minute (GPM). It can provide continuous hot water for 2-3 water supply points, making it sufficient to meet the hot water needs of a household's bathroom, kitchen, and bar area.
- No Waiting Required: Unlike traditional tank water heaters, tankless water heaters eliminate the need for a 30-minute preheating wait time, allowing you to have unlimited hot water on demand.
- Provides 4 modes: Dish mode(100), Fruit mode(95), Elderly mode(104) and Infant mode(107). More convenient for you to use.
- Save Money: The kit already includes the exhaust pipe, so you don't need to spend extra money on purchasing it separately. With an oxygen-free copper water tank, it reduces heat loss and lowers energy consumption. Applied with standard 1/2" NPT water fitting and gas inlet.
- Recommendation: We strongly advise that all installations of the device adhere to local building and plumbing regulations at the installation location, and should be carried out by licensed professionals.(Not recommended for areas over 2,000 feet)
2. Ranein Natural Gas Tankless Water Heater with Vent Pipe, Indoor Max 4.3 GPM, 100,000 BTU Instant Hot
- Performance: The on-demand tankless water heater boasts a heating capacity of 100,000 BTU and a hot water flow rate of 4.3 gallons per minute (GPM). It can provide continuous hot water for 2-3 water supply points, making it sufficient to meet the hot water needs of a household's bathroom, kitchen, and bar area.
- Upgrade Features: Four Seasons Function: Automatically adjust the water temperature output based on the seasonal water temperature changes. Kitchen Function: Default water output temperature is 100F, suitable for kitchen use. Bathtub Function: Adjustable water output quantity with a reminder when the set output quantity is reached, catering to various environmental needs.
- No Waiting Required: Unlike traditional tank water heaters, tankless water heaters eliminate the need for a 30-minute preheating wait time, allowing you to have unlimited hot water on demand.
- Save Money: The kit already includes the exhaust pipe, so you don't need to spend extra money on purchasing it separately. With an oxygen-free copper water tank, it reduces heat loss and lowers energy consumption. Applied with standard 1/2" NPT water fitting and gas inlet.
- Recommendation: We strongly advise that all installations of the device adhere to local building and plumbing regulations at the installation location, and should be carried out by licensed professionals. Not recommended for areas over 2,000 feet.
3. ThermoMate CZ422NG Natural Gas Tankless Water Heater, Up to 5 GPM 113,000 BTU, High Efficiency
- [Max 5 GPM & 113,000 BTU] - The ThermoMate instant hot water heater can supply two showers simultaneously, each delivering 105F water at a flow rate of 2 GPM, based on an inlet water temperature of 65F. No waiting time, no cold water shocks, perfect for busy households. Adopting advanced water flow sensor, the built-in chip can adjust the heating power 20,000 times per second, ensuring that the hot water within 1 fluctuations for a comfortable shower experience.
- [Safety & Reliable] - This gas tankless water heater integrates 8 protections: boil-dry, freeze, flame-out, overheating, over-temperature, pipe blockage, high-temperature lock, and excessive air pressure. Equipped with 4 ceramic heating cores, it auto-activates frost protection when temperatures hit 41F (5). The energy-smart system uses minimal electricity to generate gentle warmth, preventing pipe ice buildup without high energy costs.
- [Energy Efficient & Save Money] - The heat exchanger is constructed from high-quality oxygen-free copper, providing superior thermal conductivity and corrosion resistance compared to stainless steel. It achieves a thermal efficiency of 98% (vs. 80% for stainless steel models) and boasts a uniform energy factor (UEF) of 0.81. This design reduces energy waste, lowering annual operating costs by approximately 30% versus traditional systems.
- [Smart Diagnostic Display] - Equipped with a 3.5-inch LED touchscreen, it allows you to effortlessly adjust and monitor output water temperature90F to 140Fwhile providing real-time tracking of water flow, fan operation, and flame status. Advanced error code technology enables rapid diagnosis of water heater malfunctions. The UL-certified 120V/5-foot power cord ensures continuous power supply for real-time monitoring systems.
- [Easy to Install & Save space] - The whole house tankless water heater features standard 3/4" NPT water inlet/outlet connectors, a 1/2" NPT gas inlet, a 3" OD vent, and a UL-approved 120V plug, ensuring compatibility with most households. With its compact dimensions of 21"H x 13"W x 7"D, the on-demand water heater requires less than one-third of the space occupied by traditional tank models, freeing up valuable room in your home.
- [Wind Resistant] - Engineered with a DC High-speed Fan (360Pa static pressure/3000 RPM), the system ensures powerful exhaust evacuation capable of withstanding winds from a major hurricane (Category 3 and above, >111 mph/178 km/h), eliminating safety risks like backdraft and flameouts during the most extreme weather.
4. FOGATTI Natural Gas Tankless Water Heater Outdoor - Max 8.1 GPM 180,000 BTU, CSA Certified Compact
- Instant Hot Water: Say goodbye to preheating delays! FOGATTI tankless water heater delivers continuous hot water instantly, powered by 180,000 BTU and up to 8.1 GPM flow rate. Whether its for showers, sinks, or appliances, even for 3-5 outlet points, it ensures uninterrupted hot water
- Built for Outdoor Durability: Designed specifically for outdoor installation, this tankless water heater gas features a remote control panel for convenient indoor operation. The bottom-mounted fan enhances safety, durability, and lifespan by preventing smoke backflow and ensuring stable combustion, making it reliable in all seasons
- Precision Temperature Control: With advanced water servo technology and temperature sensors, the tankless gas water heater precisely adjusts water flow and gas intake to maintain a temperature difference within 1. The four-stage combustion system ensures consistent comfort, whether its a chilly winter or a hot summer
- Quick and Easy Installation: The compact design measuring 26.2 x 17.1 x 7.1 inches makes installation hassle-free. The gas tankless water heater is compatible with low water pressure from 15-150 PSI, ensuring smooth operation even in areas with weaker water pressure. Simply connect to a standard 120V AC for seamless operation
- Trusted Quality and Support: Built with a high-efficiency oxygen-free copper heat exchanger and 304 stainless steel burner, this tankless water heater gas outdoor offers exceptional durability and performance. Certified by CSA and equipped with multiple safety features, it meets the highest safety standards, ensuring reliable and secure operation
- Reliable Protection and Support: FOGATTI water heater includes 2 years of full coverage for the entire unit and 5 years of coverage for the heat exchanger. Our dedicated customer support team is ready to assist with any questions or concerns, providing peace of mind for you
- Note: Natural gas tankless water heater is equipped with active heating anti-freeze device, If enviroment temp drop below 5 or not be used for long period, drain the water inside to prevent damage. For optimal performance, recommended for use below 2000 feet altitude
5. 2025 GEN II Ranein Natural Gas Tankless Water Heater Max 3.6 GPM, 80,000 BTU Indoor On Demand
- Endless Hot Water for Home Multi-Scenes: Boasts a max 3.6 GPM and 80,000 BTU for 23 taps (shower + kitchen sink + bar)no more hot water shortages for daily household use.
- No Sudden Temp Changes, Stable Experience: Advanced tech maintains steady water temperature; no sudden spikes or dropsideal for showering or bathing infants comfortably.
- Cut Down Monthly Utility Bills: Heats water on-demand, cutting standby energy waste versus traditional tank heaterslowers monthly gas/electric bills and supports eco-living.
- Space-Saving for Small Spaces: Compact wall-mounted model fits apartments, small homes, or renovationsfrees up floor space while providing reliable on-demand hot water.
- One-Click Specialized Modes: 4 preset modes (Dish 100F / Fruit 95F / Infant 104F / Elderly 107F)no manual adjustments needed for different daily needs.
- Save Money on Extra Costs & Energy: Kit includes exhaust pipe (no extra purchase needed); its oxygen-free copper tank cuts heat loss to lower energy use, fitting standard 1/2" NPT water and gas ports.
- Professional Installation Advice: Must be installed by licensed professionals per local building and plumbing codesnot recommended for areas above 2,000 feet elevation.
6. Tankless Water Heater, Novieex On Demand Water Heater Natural Gas, Up to 4.3 GPM, 100,000 BTU
- Reliable Hot Water on Demand With 100,000 BTU power, this on demand water heater delivers up to 4.3 GPM instant hot water. You can comfortably run a shower, kitchen faucet, and bathroom sink simultaneouslyall without any noticeable temperature drop.
- Precise Temperature Control Enjoy consistent water temperature with a wide adjustable range from 95F to 149F, 1 temperature control . The built-in digital thermostat of the tankless water heater ensures your water stays at the desired setting, delivering comfort and safety for every shower and household task.
- High Efficiency, Lower Bills Say goodbye to the energy and electricity waste of traditional heaters that reheat water nonstop. By leveraging a selectional burner system, our tankless water heater gas precisely adjusts the flame for the water temperature. You will see a noticeable drop in your energy bills, making it an efficient and cost-effective choice.
- All-Round Security SystemOur built-in multi-protection system safeguards against gas leaks, overheating, dry-firing, and freeze damage, offering ultimate safety and comfort for families with temperature-sensitive elderly or kids with delicate skin.
- Compact & Space-SavingCompared to bulky traditional tanks, our natural gas on demand water heater is wall-mounted, saving over 50% of space and blends seamlessly into utility rooms, basements, or closets. Its sleek appearance and LED touchscreen interface allow for easy and intuitive operation.
- Usage Reminder For safe and efficient use, this indoor on demand water heater requires natural gas and professional installation by a licensed technician using 1/2" NPT fittings (Exhaust pipe included).
7. ORBEK ORBEK Natural Gas Tankless Water Heater - Max 4.3 GPM 100,000 BTU Indoor Installation - CSA
- Endless On-Demand Hot WaterThe Orbek tankless water heater gas indoor delivers 100,000 BTU capacity with 4.3GPM high flow rate, featuring innovative 0.53GPM low-flow start technologyonly. It can provide a continuous supply of hot water to 2-3 outlets at the same time, making it suitable as a whole-house water heater or a practical gift for friends and family
- Efficient & Energy-SavingThe highly efficient oxygen-free copper heat exchanger heats water rapidly, while a built-in chip intelligently adjusts the water temperature 20,000 times per second, keeping fluctuations within 1F to provide a stable and comfortable water flow. It also keeps stable combustion even at low flow rates, achieving efficient energy utilization
- Certified Safety & ReliableThe gas tankless water heater is CSA certified, meets stringent North American safety standards, and integrates multiple protections including anti-dry burning, anti-overheating, anti-leakage, anti-flameout, and anti-high water pressure. Whether showering, washing, or using water in the kitchen, you and your family can enjoy a stable supply of hot water with peace of mind
- Easy Installation & UseThe tankless water heater's compact design (20.5"H x 13.0"L x 7.0"W) blends seamlessly into homes, cottages, and apartments. The gas tankless water heater fits standard 3-inch exhaust pipe, 3/4-inch NPT connector, and 120V household power, it's designed for indoor installation only. We recommend professional installation to help you can enjoy reliable and comfortable hot water instantly
- Convenient & Worry-freeA 2-year protection on the entire unit and a 5-year protection on the heat exchanger provide you with reliable support. The gas water heater is equipped with a smart remote control and LED display, you can easily and precisely set the water temperature, and there's no need to reset it after a power outage. Its low-noise operation and energy-saving features create a quiet and worry-free home environment for you
8. Natural Gas Tankless Water Heater, Indoor Max 4.2 GPM, 102,000 BTU On Demand Instant Hot Water
- Endless Hot Water for Every Home NeedDelivers 4.2 GPM & 102,000 BTU to power 2-3 simultaneous taps (shower + kitchen sink + bar sink). No more waiting for hot water or running out mid-showerperfect for daily household use, from morning routines to evening dishwashing
- Stable Temperature, Comfort for AllAdvanced temperature control tech eliminates sudden spikes or drops. Enjoy consistent warmth for relaxing showers, and keep bath time safe & cozy for infants or kidsno more unexpected cold blasts
- Slash Monthly Utility BillsOn-demand heating cuts standby energy waste (a big flaw of traditional tank heaters). Lower your gas/electric bills month after month while reducing your carbon footprinteco-friendly living that saves you money
- Space-Saving Design for Small SpacesCompact wall-mounted unit fits perfectly in apartments, small homes, or renovation projects. Free up valuable floor space without sacrificing reliable hot waterideal for tight laundry rooms, bathrooms, or kitchens
- Easy Compatibility & Energy EfficiencyFits standard 3" OD vents, 120V AC, and 1/2" NPT fitting sizeworks with most U.S. homes. Features an oxygen-free copper tank to minimize heat loss (boosts energy efficiency). Note: Vents and water valve kit are not included
- CSA-Certified Safety You Can TrustThe natural gas tankless water heater indoor is CSA certified and packed with advanced safety features, including dry burning protection, overheating protection, timeout protection, flame out protection, and water pressure protection etc. Use it with total peace of mind
- Important Installation NotesMust be installed by a licensed plumber/contractor to meet local building & plumbing codes. Not recommended for areas above 2,000 feet elevation (due to altitude impacts on performance)
- Reliable Protection and SupportThe LiberLive natural gas water heater comes with a comprehensive 2-year warranty that covers the entire unit. Our dedicated customer support team is always on hand to address any questions or concerns, ensuring you enjoy complete peace of mind
9. FOGATTI Natural Gas Tankless Water Heater Indoor - Max 7.5 GPM 170,000 BTU, CSA Certified Compact
- Powerhouse Performance: The FOGATTI tankless water heater takes up a third of the space of traditional tank heaters but delivers 5 times the performance. With a high heating power of 170,000 BTU and a flow rate of 7.5 GPM, it provides endless hot water on demand, perfect for multitasking households
- Instant Heating: Unlike traditional tank heaters, this tankless water heater gas delivers instant and endless hot water as water flows through. Whether its for showers, sinks, or appliances, even for 3-5 outlet points, it ensures uninterrupted hot water whenever you need it
- Precision Temperature Control: With advanced water servo technology and temperature sensors, the gas tankless water heater indoor precisely adjusts water flow and gas intake to maintain a temperature difference within 1. The four-stage combustion system ensures consistent comfort, whether its a chilly winter or a hot summer
- Quick and Easy Installation: The compact design measuring 25 x 16.3 x 7.3 inches makes installation hassle-free. Tankless gas water heater is compatible with low water pressure from 15-150 PSI, ensuring smooth operation even in areas with weaker water pressure. Simply connect to a standard 120V AC for seamless operation
- Trusted Quality and Support: Built with a high-efficiency copper heat exchanger and 304 stainless steel burner, this water heater offers exceptional durability and performance. Certified by CSA and equipped with multiple safety features, it meets the highest safety standards for reliable operation
- Reliable Protection and Support: The FOGATTI natural gas tankless water heater includes 2 years of full coverage for the entire unit and 5 years of coverage for the heat exchanger. Our dedicated customer support team is ready to assist with any questions or concerns, providing peace of mind for you
- Note: Important Usage Guidelines: Tankless water heater natural gas is equipped with active heating anti-freeze device, If enviroment temp drop below 5 or not be used for long period, drain the water inside to prevent damage. For optimal performance, recommended for use below 2000 feet altitude
10. Rheem RTG-70DVLN-3 High Efficiency Non-Condensing Indoor Tankless Natural Gas Water Heater 7.0 GPM,
- High-efficiency tankless gas water heater delivers up to 7.0 GPM, perfect for 23 bathroom homes with multiple hot water needs like showers and laundry.
- Powered by natural gas with 160,000 BTUs, this durable tankless unit ensures fast, reliable hot watereven during peak household demand.
- Designed for indoor installation, this high-efficiency tankless natural gas water heater features a durable, compact metal cabinet and supports easy wall mounting by a qualified installer.
- Hot-start programming prevents cold water bursts, making this tankless natural gas water heater ideal for back-to-back showers.
- Rheem RTG tankless gas water heaters offer high-efficiency, space-saving designs with multiple models to fit any home size, fuel type, and hot water demand.
Peter
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