10 Best 40 Gallon Water Heater Gas: Expert Picks

Customer Review: “My twenty year old 40 gallon (traditional) hot water heater finally sprung a massive leak, leading me to research LPG heaters that were available. My recollection is that the heater cost around $300 in 2005.The local big box hardware chains had heaters that began around 800 and seemed to accelerate from there. Since I live by myself, this seemed to be overkill, when I had the bright idea to look at tankless heaters. The chains had some that were even more expensive.Then, I checked Amazon. I found this 3.8 gpm / 80000 BTU heater on a black Friday price of $239, with a minor delay in delivery. For the price difference, I thought I would give it a try.I also ordered a HYDRO MASTER Tankless Water Heater Service Valve Kit (62.46) to provide fittings for the water connections.I waited a couple more days for my friend (Thank you, Andrew) to assist me in mounting and plumbing the unit in. His expertise, while not absolutely necessary, allowed me a two hour installation, with no leaks. He helped me determine additional parts necessary (PEX fittings, PEX hose, exhaust pipe and couplings available locally (around $120).(One caveat: when attaching the water valves to the unit, use teflon tape and teflon paste to seal. Do not apply too much torque when installing, it can be difficult to counter hold the connection.)All plumbed up, turned on the cold and hot water valves, plugged in the electric, turned on the LPG, no leaks. turned on the hot water spigot and the unit fired right up,I could not have asked for a better outcome.I noted on the outside of the cover, the date of purchase and the 1 year warranty. We’ll see how long it lasts.Update: after 3 months of use, I have seen my propane usage drop precipitously. This unit is perfect for me and has already saved me the cost of the unit. Will keep you posted.”

Customer Review: “I purchased this a year ago and got around to installing it in late August. Living in south Alabama, I figured this would work well for our home. For what it does, and the price of the heater, I’m very pleased. Tonight is the coldest that the water heater has seen. The water coming in was 62 degrees. The output was 127 with the thermostat set at 149. Two important things to note: 1) I have a ball valve in-line at the outlet and it is throttled back a little over half way. 2) I have a well so I don’t take showers because of the inconsistent water pressure (cut-in set at 40 psi, cut-out at 60 psi). Once I install a pressure regulator, showers will be okay.I’m giving it 5 stars because it does work, it has been cheaper to operate than the electric tank water heater that I’ve had, and it is very affordable. From September 1 through today, we’ve not used but about 8 gallons of LPG to heat water for my wife, myself, and grandkids.If you’re considering this, do be aware that 3.8GPM isn’t much water. I miscalculated the volume of water from this old well pump. In my own experience in process control, it was easy enough to regulate the temperature by throttling the output of the heater to get the desired water temp/flow rate through. So, be forewarned, if you don’t have low volume water, you may need additional throttling to slow the water down through the heat exchanger.I installed it myself within about 40 minutes. Very easy to install, however, at one point we did have LPG tank heater installed so the existing exhaust vent was used. This heater mated up perfectly with the existing exhaust stack so that was extremely beneficial.”

Customer Review: “Usually don’t write reviews but this is an acception.Me and my wife have been living in a barndominioum since we’ve been building our house. About 8 years. We’ve had 2 other water heaters installed since then and so we have some experience with them.We’ve generally used the camp type water heater that go outside but I’ve figured out a way to install and vent it safely inside, they are cheaper and did do the job, however, both of them had large temperature swings in them that made for an exciting time in the shower to say the least. It would be from goose bump cold, to lobster skin red in just a few minutes but we learned how to deal with it.So, I looked at this water heater which is close to double the price, but the display pictures show it INSIDE the house and vent outside. So, the dice and purchased the more expensive model. The first time I took a shower in it, I realized that we had something a step above those other water heaters. The temperature maintained a much more consistent temperature (I could feel some slight variation) and so I could set it at a temp that was comfortable throughout my shower. We can also adjust it to whoever is in the shower at the time. My wife likes 120 and I like 125, so simple to do too. We both experienced that best shower that we’ve had at this place in 8 years. Longevity, we’ll sees, if it will get us to the finish of our house, I’ll be satisfied.If you can afford it, it is worth the price.”

Customer Review: “My parents decided to switch to a tankless water heater. We have a medium-sized household, and the high output easily keeps up with showers, laundry, and the kitchen running at the same time. The water heats up fast and stays consistent. There are no more sudden cold bursts like we used to get with our old tank system.The smart digital display is one of my favorite parts. It’s super easy to read and lets you adjust the temperature with precision, which makes a big difference when you want comfort but also don’t want to waste energy.It’s compact and sleek too. The space gray finish looks really modern and doesn’t take up much room. Installation was straightforward, and once it was hooked up, it worked perfectly right out of the gate.What really surprised me is how quiet and efficient it is. You barely notice it’s running, and it feels like a big step up in both performance and style. If you’re tired of running out of hot water or just want to make your home more energy efficient, this one is totally worth the upgrade.”

Customer Review: “My twenty year old 40 gallon (traditional) hot water heater finally sprung a massive leak, leading me to research LPG heaters that were available. My recollection is that the heater cost around $300 in 2005.The local big box hardware chains had heaters that began around 800 and seemed to accelerate from there. Since I live by myself, this seemed to be overkill, when I had the bright idea to look at tankless heaters. The chains had some that were even more expensive.Then, I checked Amazon. I found this 3.8 gpm / 80000 BTU heater on a black Friday price of $239, with a minor delay in delivery. For the price difference, I thought I would give it a try.I also ordered a HYDRO MASTER Tankless Water Heater Service Valve Kit (62.46) to provide fittings for the water connections.I waited a couple more days for my friend (Thank you, Andrew) to assist me in mounting and plumbing the unit in. His expertise, while not absolutely necessary, allowed me a two hour installation, with no leaks. He helped me determine additional parts necessary (PEX fittings, PEX hose, exhaust pipe and couplings available locally (around $120).(One caveat: when attaching the water valves to the unit, use teflon tape and teflon paste to seal. Do not apply too much torque when installing, it can be difficult to counter hold the connection.)All plumbed up, turned on the cold and hot water valves, plugged in the electric, turned on the LPG, no leaks. turned on the hot water spigot and the unit fired right up,I could not have asked for a better outcome.I noted on the outside of the cover, the date of purchase and the 1 year warranty. We’ll see how long it lasts.Update: after 3 months of use, I have seen my propane usage drop precipitously. This unit is perfect for me and has already saved me the cost of the unit. Will keep you posted.”

Customer Review: “I purchased this a year ago and got around to installing it in late August. Living in south Alabama, I figured this would work well for our home. For what it does, and the price of the heater, I’m very pleased. Tonight is the coldest that the water heater has seen. The water coming in was 62 degrees. The output was 127 with the thermostat set at 149. Two important things to note: 1) I have a ball valve in-line at the outlet and it is throttled back a little over half way. 2) I have a well so I don’t take showers because of the inconsistent water pressure (cut-in set at 40 psi, cut-out at 60 psi). Once I install a pressure regulator, showers will be okay.I’m giving it 5 stars because it does work, it has been cheaper to operate than the electric tank water heater that I’ve had, and it is very affordable. From September 1 through today, we’ve not used but about 8 gallons of LPG to heat water for my wife, myself, and grandkids.If you’re considering this, do be aware that 3.8GPM isn’t much water. I miscalculated the volume of water from this old well pump. In my own experience in process control, it was easy enough to regulate the temperature by throttling the output of the heater to get the desired water temp/flow rate through. So, be forewarned, if you don’t have low volume water, you may need additional throttling to slow the water down through the heat exchanger.I installed it myself within about 40 minutes. Very easy to install, however, at one point we did have LPG tank heater installed so the existing exhaust vent was used. This heater mated up perfectly with the existing exhaust stack so that was extremely beneficial.”

Customer Review: “Great heater. Very dependable and I never gave to run out of hot water again”

Customer Review: “Works perfect. Saves energy, space, and water usage. I have had no issues with it and it installed very easily. Thus far i have had no issues with it.”

Customer Review: “I love having an endless tank. Only downfall with this is the smart sense it uses to recognize the water pressure for use you can’t change the temp.”

Customer Review: “I love having an endless tank. Only downfall with this is the smart sense it uses to recognize the water pressure for use you can’t change the temp. Read more”

Customer Review: “Works great for my situation. Not that difficult to install. If your water temp drops you will need to adjust the heater temp accordingly. ..Works for me!”

Customer Review: “Doesn’t save anymore gas than regular stand up heater also says can run multiple faucets at same time which is not true when taking long shower over 10 to 15 minutes water gets cold with nothing else running very unpleased with purchase go ahead and spend the money and purchase a higher quality unit”

Customer Review: “Easy installation, performed by homeowner unassisted. Works as expected.I installed maintenance valves to make annual flushing easier. Easy to install and I would recommend this heater to friends and family without hesitation.How well will it perform over time is the question? The one this replaced lasted 18 years and failed due to a computer board problem. Unfortunately the board was no longer manufactured and none available anywhere.”

Customer Review: “Installation was a breeze, works very well so far. Great price.”

Customer Review: “The first thing I want to say about this water heater is that it WILL WORK ON PROPANE, the orifice fittings to convert this Natural Gas water heater over to Propane are INCLUDED in the box! I feel like this is a huge asset that is not mentioned in the ad, at least I didn’t see it anywhere when choosing this water heater.I have been suffering (well, maybe not suffering but certainly annoyed) with a 50 gallon electric water heater for years. At the time we installed it, tankless technology was still very young and there was almost no selection suitable for our application, so I bought the biggest and best dual element electric water heater I could and wired it into the breaker panel and began my next journey. I could tell right away that 50 electrified gallons wasn’t enough for this Couple to share between the two of us. Wifey could drain that tank in one scalding hot shower, or a single bath (followed with a scalding hot rinse down) and it takes Fooorrrreeeeevveeerrr for a 50 gallon tank to heat back up with electricity, especially in the winter months when the incoming water is barely above freezing. “I took a quick shower so you would have some hot water” basically meant “You have two minutes for a lukewarm rinse down before freezing your berries off” .Then after years of this Hot/Cold, but mostly cold experience, the AO Smith Tankless came into my life. I love industrial progress. This heater was relatively EASY to install, after talking to some friends in the Trades and Plumbing industries, and watching about a dozen videos concerning Tankless heaters, I tackled the project on a Three Day Weekend. The hardest part? Wrestling the old 50 gallon tank out of the heater closet and out of the house by myself. Luckily there was already a Vent Pipe up through the roof that had been capped off so I was able to tie the vent into that. This heater is NON CONDENSING so I didnt need a drain for excess water. I did buy new valves, Inlet and Outlet pipes, and other bit of hardware which added about 200 bucks to the installation. I turned the old 240V wires into a outlet away from the heater closet. Total time invested, One day to swap the heaters and One day to tie up loose ends, convert the wiring to a wall outlet, and clean up the mess~ so about 16 hours working at an Amature DIYers pace.This heater has a Built-In filter to help prevent scaling and reduce maintenance, that is a feature that most Tankless heaters do not include (and add about 150$ to the cost of installation if you want to include an in-line filter). The hot water production is marvelous. I have not had this for a year, but I am convinced it it saving me money. I am not heating an excessive amount of water and electricity gets more expensive every year.Overall, I couldn’t be happier with it and I give it my Stamp of Approval and would give a Recommendation to anyone.”

Customer Review: “After extensive research and hands-on experience, this AO Smith tankless water heater has proven to be an excellent upgrade, especially for households concerned about long-term performance and mineral buildup. One of the standout features, and the main reason this model rises above many competitors, is its built-in scale prevention system. For anyone living in an area with hard water, scale buildup is one of the biggest threats to efficiency, longevity, and consistent hot water performance. This unit addresses that issue directly, which makes a noticeable difference both immediately and over time.The integrated scale prevention technology significantly reduces mineral accumulation inside the heat exchanger. Traditional tankless water heaters often require regular descaling or flushing to prevent efficiency loss, reduced flow rates, or eventual system damage. With this AO Smith model, the scale removal and prevention system actively works to minimize buildup as the unit operates. That translates to more stable performance, fewer maintenance requirements, and greater peace of mind for homeowners who want reliability without constant upkeep. Over time, this feature alone can save money by reducing service calls and extending the lifespan of the unit.Performance-wise, the heater delivers a strong and consistent flow of hot water. It easily supports multiple fixtures running at the same time without noticeable temperature drops, which is one of the biggest advantages of switching from a traditional tank-style water heater. Showers stay consistently hot, even when appliances like dishwashers or washing machines are running simultaneously. The temperature control is responsive and precise, allowing for comfortable and predictable water temperatures throughout the home.Energy efficiency is another major benefit. This unit operates only when hot water is needed rather than constantly heating and reheating a tank of stored water. As a result, energy usage is reduced, especially for households with variable hot water demands. Over time, this efficiency can lead to meaningful savings on utility bills, making the higher upfront cost easier to justify. The design also includes advanced diagnostics and integrated controls, which help the system operate efficiently while providing helpful feedback if adjustments or servicing are ever needed.Installation is where this unit truly separates casual DIY upgrades from professional-level work. While the heater itself is well designed, installing a tankless water heater, especially one with advanced features, requires a strong understanding of plumbing, gas lines, venting, and electrical connections. Due to the complexity and importance of proper installation, hiring a licensed plumber was absolutely the right decision. The installation process involves precise venting requirements, gas pressure considerations, and safety checks that are not suited for trial-and-error approaches.Having a professional handle the installation ensured that everything was set up correctly from the start. The plumber was able to verify proper airflow, gas supply, water pressure, and system calibration. This not only guarantees optimal performance but also protects the warranty and ensures the unit meets local building codes. Given the investment and the importance of safe operation, professional installation is strongly recommended and well worth the cost.Once installed, the compact wall-mounted design immediately freed up space compared to a bulky traditional tank. The efficient footprint makes it ideal for utility rooms, garages, or mechanical closets where space is at a premium. Despite its smaller size, the system delivers more reliable performance than a conventional water heater ever could.Maintenance requirements are refreshingly minimal, especially thanks to the scale prevention system. Unlike many tankless units that require annual descaling in hard water regions, this model dramatically reduces the need for frequent maintenance. That does not mean maintenance should be ignored entirely, but it does mean less time, effort, and expense over the life of the unit. For homeowners who want a set-it-and-forget-it solution without sacrificing performance, this is a significant advantage.Safety features are also thoughtfully integrated. The unit includes multiple safeguards such as temperature monitoring, overheat protection, and automatic shutdowns if abnormal conditions are detected. These features provide additional reassurance, particularly in homes with children or high hot water usage. The system feels robust, well engineered, and designed with long-term residential use in mind.Overall, this AO Smith tankless water heater stands out because it addresses one of the biggest weaknesses of tankless systems, scale buildup, while delivering excellent performance, efficiency, and reliability. While the installation is not simple and absolutely warrants a professional plumber, the result is a high-quality system that performs exactly as intended. For homeowners looking for a premium tankless water heater that prioritizes longevity, efficiency, and low maintenance, this model is an outstanding choice and a worthwhile investment.”

Customer Review: “So far this tankless hot water has been excellent. For the price you can expect to have to replumb some of your fittings but the performance is good, especially considering the price.”

Customer Review: “Professionally installed according to Mfgr instructions cannot get 100 degrees of heat to a 1.75GPH water miser shower head on a half inch PEX output with 3/8” connections. Waste of time and money. Does niot operate according to advertisement, will not heat water to any temperature considered more than “warm”.”

Customer Review: “I don’t give reviews at all but this product is working as it should and was actually a pleasant surprise for the money. This in my repair shop behind my house and is mainly used to was our hands. it is about 6′ away from the sink but about 15′ of tubing before it reaches the sink and by the time you lather your hands you have warm to hot water. If somebody in the bathroom uses the sink you both get lukewarm water this is a good single use unit. I waited a month to post I hope it gives me years of service.”

Customer Review: “This is one of the best purchases I have made this year this works excellent hot water is continuous perfect pressure perfect temperature if you have a hot water heater you need to replace it with this tankless how water heater it works so good it comes with everything you need even the propane connection easy to install I’ve never installed a hot water heater in my life and I was able to install this by myself in about 30 minutes”