The 5 Best Tankless Gas Water Heater Reviews | The Ultimate Buyer’s Guide

Do on demand hot water heaters live up to the hype?

If you’re in the market for the best tankless gas water heater, I am sure you have been asking yourself that question. After reading tons of tankless gas water heater reviews you may feel like you’re still not close to an answer.

There are a lot of factors that go into buying an endless hot water heater and since they are not cheap, you’ve probably asked yourself, is a gas tankless water heater worth it?

I wrote this buyer’s guide to get to the bottom of this question.

Though tankless gas water heaters, in general, are a wise investment, they might not be best for everybody.

It really depends on your needs to be able to answer if they are worth it.

Read on as I will evaluate the 5 best tankless gas water heaters reviews.

Before we get into the reviews, check out the section on how to pick the right size tankless gas water heater.

If you don’t have time to read the entire article, here is a comparison table to compare brands at a glance.

Rinnai RUC98iN Ultra Series

Flow Rate:
9.8 GPM

Min. Flow Trigger:
0.4 GPM

Max BTU:
199,000

Location:
Indoors

Price:
$$$$

Check out on Amazon.com

Rheem RTG-84XLN Outdoor

Flow Rate:
8.4 GPM

Min. Flow Trigger:
0.26 GPM

Max BTU:
180,000

Location:
Outdoors

Price:
$$$

Check out on Amazon.com

Navien NPE-240-A

Flow Rate:
11.2 GPM

Min. Flow Trigger:
0.4 GPM

Max BTU:
199,900

Location:
Indoors

Price:
$$$$½

Check out on Amazon.com

Noritz NRC661-DV-NG Indoor Condensing

Flow Rate:
6.6 GPM

Min. Flow Trigger:
0.5 GPM

Max BTU:
120,000

Location:
Indoors

Price:
$$$½

Check out on Amazon.com

Takagi T-KJr2-IN-NG

Flow Rate:
6.6 GPM

Min. Flow Trigger:
0.5 GPM

Max BTU:
140,000

Location:
Indoors

Price:
$$$

Check out on Amazon.com

Before You Buy

You’ll need to know a few things about your needs and circumstances before you can zero in on exactly the right gas tankless water heater to buy. Here are a couple of things you need to know before you purchase.

What size gas line do I need?

For a typical whole house on demand hot water heater, your gas lines should be a minimum of .75 inches.

1 inch would be better.

It really comes down to BTU. A whole home unit will be up to 199,999 BTUs so that requires, again, a minimum of .75 inches.

Pressure is also a factor.

Depending on how many gas fired appliances you are running and what the BTUs are for each, you may need to swap out your meter and add more regulators to maintain a 2psi of gas pressure coming into your tankless water heater.

For most newer homes built in the last 10 or so years, gas line size will likely not be an issue. For older homes, you may be looking at a serious upgrade in your gas lines.

You will definitely need a licensed plumber to come and do an evaluation of your gas lines and your overall usage to determine if you need to upgrade your lines.

What size tankless to buy

Tankless gas water heating sizing also depends on a few things.

I know that the most annoying answer in the English language is “it depends”, but it is hard to give advice when I don’t know what you need.

So you need to do a quick evaluation to decide what size endless hot water heater you need, a sort of tankless water heater calculator if you will. 

The Top Five Gas Tankless Water Heaters To Buy

Rinnai RUC98iN Ultra Series Review

Pros

• 9.8 GPM (Gallons Per Minute)
• Incredibly efficient – Up to 0.96 Energy Factor
• Low flow rate trigger – .4GPM
• Ultra low NOx emissions
• Concentric or PVC venting option
• Long warranty – 12 years for residential

Cons

• Can only be used indoors
• Slight dip in water pressure

Getting all the hot water you need across the whole house with an on demand hot water heater can be a bit of a challenge. 

Which is why I think the Rinnai RUC98iN is the best whole house tankless gas water heater for.

Flow Rate

With a family of four or more, you can be using up to 9.8 gallons of water per minute at the same time. That means that with low flow shower heads, you can be using two showers, a sink and a dishwasher at the same time.

No more waiting to do laundry until somebody is done with the shower!

Efficient

As a condensing tankless gas water heater, it is highly efficient operating at a very generous 0.96 Energy Factor.

Adding to the efficiency is an electric pilot that only switches on once the unit detects the water flow. In some other models, there is a pilot light that always stays lit. This will keep your natural gas consumption to a bare minimum.

Make sure that if you are using low flow shower heads that they are over 0.5GPM, as the Rinnai won’t trigger. To turn on, it needs to have at least 0.4 GPM.

Installation Costs

Tankless gas water heater installation can get expensive when using a professional. Since the quotes for how much are very site specific, it is hard to put a number on it, but expect at least $2,000.

Rinnai includes extremely detailed instructions so a DIY installation can be done for a fraction of the price for a professional installation.

Since there is the option to use concentric tubes, it makes the install a bit easier since there are no heat concerns from the exhaust which stays on the inside of the two pipes.

Not only that but then only one hole needs to be drilled through the wall.

Keep in mind that some states offer an Energy Star rebate but only when using a professional to install the tankless gas water heater.

You should more than make up the difference doing it yourself.

Variable Pressure

The range of water pressure that the Rinnai RUC98iN can work with is quite generous. The lower end of water pressure being 50psi and the upper limit is 150psi. The optimal range, however, is 60-80psi.

That puts in in range for use in just about every home whether it is old or new.

Accurate Temperature Control

Temperature control is very accurate. It comes set at a default of 120°F, but can be manually switched to go up to 140°F. That is not recommended if there are young children in the house. Most people set it to 105°F for energy efficiency while still getting the water hot enough for everyday use.

Here is a chart so you can see what the temperature rise is for this Rinnai RUC98iN. With my hypothetical scenario I laid out in the how to find the right size section, you can see that the GPM flow rate is a little over 6.5 gallons to keep it at a temperature of 105° with groundwater at 47°F. That is very, very good.

Warranty

These Rinnai RUC98iN are built to last so don’t be surprised if 20 years after you buy it, it is still pumping out hot water on demand for the whole large house. The Rinnai warranty is very generous and will cover most defects up to 12 years. Compare that to a typical tank water heater that would likely never even make it to the 12-year mark.

Verdict

If you need something beefy to make sure that all of the hot water needs of your house are met, then this is definitely the best tankless gas water heater for big homes. It is pricey, but the added features make it worth the money and the energy efficiency means it will pay for itself over a few years.

If you live in a cold climate then this is going to be your best bet since a high GPM tankless heater is essential. I wrote up a long article about how to use a tankless water heater in a cold climate with 8 easy tips. If you live somewhere cold then make sure you take a look at that article before you buy.

Rheem RTG-84XLN 8.4 GPM Review

Pros

• 8.4 GPM (Gallons Per Minute)
• Low flow rate trigger – .4GPM
• Up to 0.82 Energy Factor
• A 40% thicker heat exchanger and a new burner pattern
• Self-diagnostic system for easy installation and service
• 12 year warranty

Cons

• The 2 degree increments change after 120°F to 5 degree increments

This “medium efficiency” tankless gas water heater from Rheem is a great budget option for people that don’t need to have many water sources running at once.

Flow Rate

Though, 8.4 GPM is very generous, it doesn’t have as good a temperature rise as the previously reviewed Rinnai. That GPM is with a 35° temperature rise, so if you set your temperature to 110°F for example, then your groundwater will have to be 75°F.

Which makes this one of the best tankless gas hot water heater for Southern states.

In non summer months, with a 45° temperature rise, or 65° water temperature you can expect 6.6 GPM.

Who Is It Best For?

This is one of the best outdoor tankless gas water heaters, but, in an area of the country that sees temperatures regularly dip below freezing, it is not the best option. It is rated to withstand temperatures up to -30°F, though, but since the temperature rise would diminish the GPM in a northern, cold climate, it is probably best to go for an indoor unit instead.

This is ideal for people that are going to be using at most two showers and a dishwasher at the same time, for example, and live in a moderate to hot climate.

The price is also something that makes this an excellent purchase. Not just the fact that the purchase price is much lower than other high GPM equipped on demand water heaters, but also the fact that installation can be done DIY since it doesn’t require any venting.

Easy Installation

Unless you already have some plumbing experience, make sure you read up well and watch some videos on how to hook a tankless water heater to the gas lines.

If you have an older house with old gas lines, then luckily this can be fitted to .5 inch lines. Though you will need to make sure that the pressure is at least 2psi. If you are under that, then there will be an added expense of changing your gas meter.

All tolled though, the purchase price and low cost of installation means that if you have a big house and high hot water usage, it would still be economical to buy two of these tankless gas water heaters rather than a bigger whole house inline heater.

There are some very nice convenience features, as well.

Wireless App

First, it is EcoNet enabled which means that the heater communicates to an app where you can check your usage and other stats. It will also let you know when it needs to be flushed.

Efficient

It also has Water Savings Setting, which can save you up to 1,100 gallons of water waste per year by reducing the flow rate at the tap until it reaches the temperature setting. At which point the normal pressure will kick in.

The thermostat is “remote”, which is not to be confused with having a wireless remote. It means that it can be installed inside the house, but is connected to a wire to control the unit. This is a plus so you don’t have to go outside to change the temperature or other settings.

Instant Hot Water Ready

Lastly, it is recirculation pump ready. It will need to be installed separately, but if you want instant hot water, this pump recirculates the hot water back so you will have hot water as soon as you turn on the tap.

This tankless gas water heater has the potential to save up to 12,000 gallons of water per year. Though it will increase your gas usage slightly if you opt to use it. It can be programmed to only keep the water hot during certain times of the day so it isn’t heating water when you’re at work.

Verdict

If you live in an area with hard water, there is the option of bypass valve assemblies that make it a cinch to do your yearly flush to get rid of any calcium or lime deposits.

For these reasons and more, this gets the nod for best outdoor tankless gas water heater in my book. If you live in the South, can do the installation yourself, and don’t have more than four people needing water at the same time, then it is the ideal.

Navien NPE-240-A Outdoor Tankless Gas Water Heater Review

Pros

• 11.2 GPM with 35° temperature rise
• Intelligent preheating
• .5 gallon buffer tank means no cold water sandwiches
• Indoor or outdoor installation
• Lower operating costs than any other brand
• 0.97 rated efficiency

Cons

• Very expensive

Easy to operate, huge water flow rate, extremely efficient, and smart means that this tankless gas water heater can get the job done in any size house.

Why didn’t I rate it the best whole house water heater then?

Simply because it is overkill for most people.

This unit is best for people with big families that have heavy water use every day.

If you do have a large house of 7 or more people, especially with some of them being teenagers, then you’ll be very happy with the performance.

Here are some of the features of the Navien NPE 240 A.

High Flow Rate

With a whopping 12.2 GPM flow rate with a 30° temperature rise, there simply is no other tankless gas water heater that can compete.

If you live in a very cold area with a high-temperature rise from cold groundwater, then you can’t do any better than the Navien NPE 240 A.

For example, if you live somewhere with really frigid 45°F groundwater and set it at 105°F then you will get a very impressive 6.5 GPM flow rate. Add some low flow shower heads into the mix and you are looking at multiple showers, a faucet, and dishwasher running at once.

Intelligent Preheating

A common complaint among tankless heater owners is that there is too much water wasted while waiting for the hot water to arrive where it’s needed.

That problem is eliminated in a very efficient and convenient way.

Smart technology allows the Navien NPE 240 A to understand when you use the most hot water. It then uses a recirculating pump with a .5 gallon buffer tank to keep a reserve of hot water ready for use.

This way you don’t have to run the water for up to a minute wasting water while waiting for it to arrive hot. You get instant hot water. No more cold water sandwiches.

The best part?

It doesn’t run the pump all day, so you won’t find your gas bill higher than normal.

Highly Efficient

Energy Star certified with a 0.97 efficiency rating is the highest you can get.

A stainless steel heat exchanger brings the water up to temperature more quickly than copper.

Most tankless gas water heaters will give you a savings of 10 to 20% off your normal gas bill, but the Navien NPE 240 A goes way beyond that by using a condenser as well.

Long Lasting

When the condensation mixes with the exhaust gases, you end up with a highly corrosive mix.

The stainless steel heat exchanger will not corrode or rust from this mix. Thus, you get many years out of this exchanger.

In fact, Navien offers a 15-year warranty, which is the longest in the business. Expect to get at least a couple of decades of instant hot water.

Easy to Use

With the mobile app, you can set your temperature with your smartphone quickly and easily.

You can monitor your usage and even get alerts when there may be a problem.

Temperature control is very accurate and can be raised in 1° increment for precise control. From 98° up to 140°.

Troubleshooting any potential problems can sometimes be done with the push of a button on the app which saves a visit from the plumber.

Installation

You can save quite a bit of money by doing your own installation, but be advised that you nullify the warranty if something goes wrong when you do it yourself.

That said, however, you save a ton by doing it yourself which may offset the cost of the unit.

Navien has made it easy to do yourself, or with a professional by giving you everything you need to do the installation right in the box.

All you need to get are the hoses.

Making it very versatile is the fact that it can be used even in old homes with 0.5 inch gas lines and up. And the 2 inch PVC tubes for the intake and exhaust can give you up to 60 feet. Or, if you need more length than that, there is the option to use 3 inch PVC, which gives you up to 150 feet to exit the building.

Versatility

For added convenience, you can use this unit inside or out. For outside, you will need to get an outdoor vent kit which is sold separately.

Not only that, but you can use either natural gas or switch it to liquid propane, whichever suits your needs best.

Verdict

For most people, this unit will be overkill.

For everyone else that either lives in a very cold area or has a lot of people that use hot water at once, then this unit simply cannot be beat.

Yes, it is very expensive. But, if you use a lot of hot water then this will definitely pay for itself after a few years.

Noritz NRC661-DV-NG Indoor Condensing Review

Pros

• High Efficiency 0.92 rating
• Small profile for space saving
• 6.6 GPM flow rate
• 9 Temperature settings from 100° to 140°
• 0.5 GPM low flow trigger setting
• Economical price

Cons

• Slow to get hot water to tap
• Fittings are sold separately

Apartment dwellers and empty nesters will love this high efficiency natural gas tankless hot water heater.

Noritz NRC661-DV-NG is a condensing tankless water heater that is ideal for those that need a reliable unit at a great price.

Flow Rate

With a 6.6 GPM flow rate at a 30° temperature rise, you can service a two bathroom home easily.

Here is a handy chart to see what the temperature rise and flow rate is.

As you can see, this is really meant for a house with two to three people or houses located in the Southern states where the groundwater is not that cold.

If you live in the North and have a groundwater temperature of 50° coming into the unit, and keep your water temperature set at 105° then you drop down to roughly 4GPM. Which would get you two low flow showers running at the same time as a faucet.

Space Saver

When you live in a smaller home and space is of the essence, you will love the small profile of the Noritz NRC661-DV-NG. It is 20.5” (H) x 13.8” (W) x 6.7” (D) and takes up about the same amount of space as a medium size suitcase. Mount it in a closet, basement or garage and you’ll not sacrifice any precious space to it.

Efficient

At an Energy Star 0.93 efficiency rating, it will easily pay for itself in a few short years as you see your gas bill decline.

Expect savings of roughly 10 to 20% off of your old bill and you can see how it adds up.

Installation

Whether for you or for a professional plumber, the instructions included are incredibly detailed to make sure it goes in easily.

It’s hard to say what the installation cost is for a professional, but if you do it yourself, you can save quite a bit of money. Add those savings to the low cost of the unit and you have a great bargain.

Making your installation even easier is the PVC vents. They are much easier to go through the wall since you can use a sealant for a tighter fit. Stainless steel vents get hot and require some precision to get them safely through the wall.

Cost

Talking about cost, this is one of the lowest prices for the quality you get and for similar GPM units.

In fact, if you have higher hot water demands, it may even make sense to buy two of these units instead of one larger one.

With a 12 year warranty, it is built to last and will easily outpace a 40 gallon tank boiler.

Verdict

For those with low hot water demand, this is about as good as it gets. The Noritz brand is reliable and their customer service is top notch.

You don’t have to go overboard spending on a bigger tankless heater when you don’t need it. If this fits your water usage needs, then I highly recommend it.

Takagi T-KJr2-IN-NG Indoor Tankless Water Heater Review

Pros

• 6.6 GPM with 35° temperature rise
• Temperature can be set up to 165°F
• Very small profile
• Easy installation
• Great low price
• Very low operating costs

Cons

• Not Energy Star certified

If you don’t have a very high hot water demand household, then there are not many reasons why you shouldn’t be considering the Takagi T-KJr2-IN-NG small tankless water heater.

For the power you get out of a small unit, it is ideal for two bathroom homes.

Let’s dive into the features.

Flow Rate

With a 35° temperature rise, the water flow rate is a respectable 6.6 GPM. If you have your temperature set for 105°F and you have groundwater coming into the unit at 70°F then that means you can have 2 showers running simultaneously. And more if you’re using low flow shower heads.

This is ideal for those living in the South or for Northerners with two adults in a smaller home.

Saves Space

Only the size of a suitcase, this can fit in just about any space that keeps it out of the way. As long as it can vent horizontally outside. Keep it in a corner of the basement or in that utility closet.

Since it is off the ground, you’ll hardly notice it is there and can use that extra space for more storage.

Safety Protection

This is an indoor unit, and shouldn’t be installed outside. But, there are times when you may lose your heat and still can get hot water on demand even if the temperature in the house drops below freezing. It has a system that kicks on to warm the heater if it detects air temperatures below 36°F.

There is also a surge protection system to protect the unit for burning out.

Efficient

This is where the Takagi T-KJr2-IN-NG comes up somewhat short when compared to other gas tankless water heaters.

It is fairly efficient, but is not Energy Star certified. You should see some savings on your gas bill as it is rated .83 energy factor.

This is definitely more efficient than it needs to be when there are not many people living in the home, however.

Installation

If you need to set this up yourself, you will be lead step by step with very detailed instructions. Even the hon handy among us rarely report any trouble with the installation.

The only problem with installing yourself is that you void the warranty if something goes wrong. However, with the low price of this small tankless natural gas hot water heater, it may make more economic sense to take that chance. After all, installation will likely be more than what you paid for the Takagi T-KJr2-IN-NG anyway.

Since the installation is fairly straightforward, it won’t cost as much as similarly sized tankless water heaters either.

Warranty

If you do opt for a professional installation, the Takagi T-KJr2-IN-NG is backed up by a nice 10 year heater exchange warranty.

Verdict

This is the best small tankless water heater when you are on a budget. If you don’t want to spend much on a large on demand water heater that is more than what you need, then you won’t be disappointed by how well this works.

For cheap tankless water heaters, there are not many that can compete with the durability and quality engineering that you get with the Takagi T-KJr2-IN-NG.

What Are Tankless Gas Water Heater Costs?

How much a tankless gas water heater costs is hard to pin down since there are a lot of variables.

Let’s take the size of the unit, for instance.

The cost of the actual on demand hot water heater ranges from less than $200 for the smallest size to over $2000 for some whole house tankless water heaters.

On the higher end of the price spectrum are condensing tankless gas water heaters which bring the cost up even higher.

How much does it cost to install a gas tankless hot water heater?

Again, this depends on many variables.

Where you live is a big factor as you will pay more to have one installed in Boston than you will pay in Tulsa, for instance.

The installation will also depend on how big your gas lines are and how big they need to be to accommodate the gas heater.

Gas models are generally more expensive than electric tankless heaters as they require venting. This is more labor intensive and requires parts that add to the expense.

A good ballpark figure to keep in mind is it will likely cost between $1,000 to over $4,000. You will need to identify what kind of heater you need and then you can narrow down exactly how much it will cost.

How much the gas tankless water heater costs to operate also depends on local factors. The cost of propane and natural gas will vary depending on your region.

And, generally speaking, the cost of natural gas is less than propane when considering how many BTUs you get for the money.

Operating costs, then, should cost less for a natural gas tankless than a propane one. Again, this is in theory and I can’t really pin down a set price on how much it costs to run a tankless gas water heater.

Wrapping it Up

It may seem daunting to find the best tankless gas water heater as there is a lot to consider.

You’ve probably been reading tons of gas tankless water heater reviews.

Is a gas tankless hot water heater worth it?

Look, these gas endless hot water heaters are not for everybody.

It comes down to this.

If you live in an old home and need to replace or upgrade a lot of gas lines, then it probably isn’t going to be worth it.

Yes, tankless last more than twice as long as a standard, so in theory, it should pay for itself over time.

Again, though it depends on how much it costs to install. You may be better off with an electric tankless water heater.

If you have a newer house and are ready to get rid of an older boiler, then I think this is a perfect time to consider getting a tankless water heater.

I hope this tankless gas water heater review helped you.

If you still have questions, drop a line in the comment box below and I will get back to you as soon as I can to help answer your questions!