If you’re still using a tank storage for heated water, upgrading to a tankless system is probably the best investment you can make for your home. You’ll finally be able to enjoy instant hot water instead of having to wait 20-30 seconds after turning on the faucet. Tankless heaters also take up less space, require less maintenance and last twice as long as tank storage units.

ProductImageReview Score 
Rinnai RUC98iN Ultra Series Natural Gas, Concentric/Twin Pipe Installation 9.6Check Price on Amazon
Takagi T-H3 Condensing High-Efficiency Natural Gas Indoor, 10-Gallon Per Minute 9.5Check Price on Amazon
Eccotemp FVI-12-LP High Capacity Propane9.4Check Price on Amazon
Rinnai RL94iN Luxury Series Natural Gas

9.3Check Price on Amazon
Westinghouse WGRTNG199 199K BTU Natural Gas High-Efficiency9.2Check Price on Amazon
Takagi T-K4-OS-NG 9Check Price on Amazon
Rinnai V65EP Outdoor Low NOx – Propane 8.8Check Price on Amazon
Takagi T-T-KJr2-OS-LP 8.7Check Price on Amazon
Rheem RTG-84XLP 8.4 GPM Low NOx Outdoor – Propane8.5Check Price on Amazon
Noritz NRC661-DV-NG Indoor Condensing – Direct 6.6 Gpm-Natural Gas 8.4Check Price on Amazon

According to the U.S. Department of Energy, on-demand (tankless) water heating can save $100 per year for an average family of four. Considering that natural gas heaters have a life expectancy of 25-35 years, the savings are even greater in the long run.

Of course, not all on-demand heating systems are created equal. And with hundreds of models and modifications to choose from, shopping for one can be totally overwhelming.

If you’re in the market for a gas, you probably have a lot of questions. Why are some units so much more expensive than others? How do you install and maintain a gas system? What’s the best model for your home?
Well, fortunately for you, this guide has all the answers and more.

How to Choose

First and foremost, you should only consider heaters made by reputable and dependable brands. After all, it’s a product you will use every day for the next 30 years.
There are many other factors you should take into account before you buy. The most important must-know modifications are outlined below.

Water Flow Rate

Measured in units of GPM (gallons per minute), the flow rate determines how much hot water can run at the same time. The average shower has a flow rate of 1.5 GPM, while the average kitchen sink uses 1 GPM.

For example, if your home has two showers, you need a heater with a maximum capacity of 4 GPM or greater. Otherwise, two people won’t be able to shower at the same time while someone is washing the dishes or vise versa.


The ambient temperature of water from the grid is stable all year long with the exception of below-freezing weather. For obvious reasons, if you live in a colder climate, you will need a more powerful heater. Ideally, it should be able to heat water to 150° F at your maximum flow rate on the coldest winter day.

If you’re worried about gas efficiency – don’t be. Most tankless heaters are compatible with electronic controllers that let you dial down the gas burner.

Gas Supply

Not all heaters are compatible with low-capacity gas supply lines. So make sure to check whether your existing line would support a gas water heating machine. If it isn’t sufficient, you will need to get it replaced with an upgraded version.


Every gas-powered heater has a certain ventilation rate requirement. They only run on clean-burning natural gas but the fumes still require an exhaust. As such, you’ll need to install an adequate venting system.

Top Rated On The Market Today

1.  Rinnai RUC98iN Ultra Series (Check Price on Amazon.com)

Rinnai has been the leading gas heater manufacturer for over two decades now. And their Ultra Series is the most efficient gas burner ever made. The Energy Star Qualified heater uses condensing technology for 96% thermal efficiency, which is 15% above standard tankless gas units.

At 199,000 BTU, the RUC98iN is the largest Ultra Series model available. It has a heating range of 98° F to 140° F with the capacity to easily handle multiple water sources. And reliability is backed by a 5-year manufacturer warranty for all parts as well as a 12-month warranty on labor.

It’s also an RUR model, meaning it features Rinnai’s ThermoCirc360 technology for virtually instant hot water from the second you turn on the shower/faucet. The system comes complete with a built-in recirculation pump, an internal bypass line, and an optional dedicated return line.

Annual maintenance is simplified thanks to the heater’s isolation valves. The Ultra Series is compatible with both Concentric Polypropylene and dual-pipe PVC/CPVC venting system. However, it must be installed on an exterior wall in order to vent outside.

2.  Takagi T-H3 Condensing (Check Price on Amazon.com)

The Tagaki T-H3 is perfectly suited for both residential and commercial applications. It is compact, yet powerful enough to heat four bathrooms.

With a gas input of 199,000 BTU, it can heat a maximum of 10 GPM of water in warm climates and 5.4 GPM in cold climates. And Takagi’s condensing technology allows the heater to work at 95% thermal efficiency.

The primary heat exchanger is made from industrial-grade copper alloy, which has heat transfer rate that’s 25 times better than stainless steel. Meanwhile, the secondary exchanger is made of rugged 316L steel for improved corrosion resistance.

If you use the NSF Certified heater commercially, Takagi covers the heat exchanger with a 6-year warranty. For residential use, that warranty is extended to 15 years. And, in both cases, all other parts are also covered for 5 years.

3.  Eccotemp FVI-12-LP (Check Price on Amazon.com)

Eccotemp’s FVI is powered by liquid propane. As such it doesn’t require a gas line and is easier to install. Likewise, thanks to its integrated exhaust fan there’s no need for an external venting system.

Designed for small homes, vacation cabins and cottages, this heater lacks the capacity for large-scale use. In cold climates, the FVI-12-LP can operate at a maximum of 2.3 GMP.

The convenient digital thermometer display and manual water temperature controls allow you to adjust heating levels with precision. Both the exhaust fan and the digital display are powered by electricity. But the FVI-12-LP only uses 2 watts and 1.07 amps so it’s totally safe to plug it into a standard 120V outlet.

Being a propane-powered model, this heater is much more affordable than standard gas tankless units. Not to mention the fact that installation is free and yearly maintenance is not required.

4.  Rinnai RL94iN Luxury Series (Check Price on Amazon.com)

The Luxury Series is Rinnai’s most high-end residential heater line. The RL94iN has an adjustable gas intake rate of 9,000-199,000 BTU and a 9.4 GPM maximum flow rate. In warm climates, it can heat water for up to five bathrooms to 98°-140° F.

Its integrated Circ-Logic recirculation system cycles an external pump at pre-set intervals, minimizing gas usage. Compatible with both liquid propane and natural gas, this water heater has a thermal efficiency rating of 82%.

To guarantee a long life, Rinnai equipped the Luxury Series heater with Enhanced Scale Detection. It even has a sensor that indicates the possibility of external or internal corrosion. If there’s a possibility of serious damage, the RL94iN shuts down altogether unless you bypass the Enhanced Scale Detection warning.

It uses a concentric ventilation system, requiring it to be mounted externally. Thankfully, there’s a temperature lock function for preventing accidental and unauthorized changes to water temperature.

5.  Westinghouse WGRTNG199 (Check Price on Amazon.com)

The Westinghouse WRGTNG199 is an Energy Star certified heater with an impressive 11 GPM water flow capacity in warmer climates. It comes in configurations for both liquid propane and natural gas.

While this model is best suited for commercial use, it had highly adjustable heating levels that also make it a great for the home. In fact, you can adjust the temperature in 1° F increments.

If you’re hesitant to buy a gas-powered unit because of safety concerns, this Westinghouse is bound to change your mind. It features a wide range of safety functions, including a state-of-the-art gas leak detection system and switch-mode power supply capability. In addition to that, it has a two-stage antifreeze mechanism designed for the coldest climates on Earth.

With a 98% thermal efficiency rating, it is also among the most efficient tankless heaters in its category. However, it requires high capacity venting and installation tends to be difficult.

6.  Takagi T-K4-OS-NG (Check Price on Amazon.com)

Takagi’s portable heater line, the T-K4, is perfect for small to mid-sized homes. Its 190,000 BTU water input and 8.0 GPM capacity allow it to accommodate three bathrooms in warm climates or two bathrooms in colder climates.

The T-K4-OS-NG was designed specifically for outdoor use, though it can be modified for indoor domestic applications with the help of a few accessory parts.

Unless you plan to modify it for indoor use, there’s no venting system requirement for this heater. It can be used outdoors all year around. Its antifreeze system guarantees safety in the winter, while the overheating protection does so in the summer.

This heater has integrated sensors that constantly readjust heating levels as temperature changes. It comes standard with a convenient remote control so you don’t have to go outside to turn the heat up/down.

7.  Rinnai V65EP Outdoor (Check Price on Amazon.com)

This Rinnai is a portable unit with a 150,000 BTU gas intake. In warm climates, it can handle up to 6.6 GPM of water, which is enough for up to four bathrooms.

Though it is still a gas-powered appliance, the V65EP complies with South Coast Air Quality NOx emission standards. That means it doesn’t emit a lot of greenhouse gasses and it doesn’t worsen air quality.

Measuring 9 x 14 x 23 inches, it is one of the most compact gas heaters on the market. It also weighs just 52 pounds and is certified for use in mobile homes.

It also comes with a digital controller that saves the last heating levels you dialed in in the case of a power outage.

8.  Takagi T-T-KJr2-OS-LP (Check Price on Amazon.com)

The Takagi T-T-KJr2 is a fully modulating outdoor. It was made for light use and is best suited for vacation cabins and cottages or small homes located in warmer climates.

With enough capacity for two bathrooms and a gas intake of up to 140,000 BTU, this heater is one of the most efficient outdoor units out there. Powered by liquid propane, it has an 82% thermal efficiency rating.

It is fully covered by Takagi’s 5-year parts warranty as well as a 15-year heat exchanger warranty.

This includes a remote control for easy outdoor access. But, for some reason, it doesn’t include all the parts needed for outdoor installation. Keep in mind that installing the tankless heater on your own will void the warranty unless you are a certified professional.

9.  Rheem RTG-84XLP (Check Price on Amazon.com)

Rheem’s RTG series is among the biggest best-sellers in its class, and for good reason. It’s an outdoor heater that runs on liquid propane, yet it is able to cycle water at 8.4 GPM. It even employs a recirculation pump system that improves performance in cold climates.

It has an exclusive Water Saver setting that can save up to 1,100 gallons of water per year. Plus, intelligent electronic controls help save gas. The heater is rated at 84% thermal efficiency.

This product has low flow capability for use with limited water sources. It’s minimum flow rate is just 0.26 GPM. It also comes with 10 feet of thermostat wiring as well as a UMC remote control.

10.  Noritz NRC661-DV-NG (Check Price on Amazon.com)

This Noritz gas is ideal for indoor use. It can deliver up to 6.6 GPM of water flow for up to three bathrooms in warmer climates.

It requires special exterior ventilation, but only because this is a condensing model. Condensing heaters have extremely high-efficiency ratings and the NRC611 is no different. They also produce a cool exhaust instead of hot, which will give you more options when choosing a ventilation system.

It is highly recommended to have a professional install this, though it’s possible to do it yourself. The heater vents through PVC and works well overall. In addition to being efficient, it keeps condensation low. Overall an amazing option for larger hot water needs, especially considering its low cost.