Best Indoor Tankless Gas Water Heaters in 2021

If your water heater comes with a 12-year warranty and today is its 20th birthday, it might be time to replace it. Nowadays, there is an infinite number of water heater models out there. The most energy-efficient models will save you tremendous amounts of money in the long run, but you might need to spend a little bit more up front.

You might need to consult with a professional to understand the current regulations regarding any efficiency standards in your country.

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

Takagi T-KJr2-IN-NG

There are several types of water heaters out there on the market, but we’re going to focus mainly on the tankless variety. This is because this is the most energy-efficient type of heater, though it does have its limitations.

The tankless type doesn’t store water for heating, but rather its heating coils heat up the water as it’s drawn. This buying guide should help you understand what a tankless water heater is and the essential features to pay attention to when purchasing one.

Indoor Tankless Gas Water Heater | Bestseller

SaleBestseller No. 1
Rinnai Tankless Hot Water Heater / V75IN / Natural...
Rinnai Tankless Hot Water Heater / V75IN / Natural...
Up to 7.5 GPM hot water flow rate (varies by groundwater temp)

Available Floor or Mounting Space

Although tankless water heaters are much more compact compared to traditional ones, it’s still essential to determine whether you have enough room in your home to accommodate a tankless model. Gas-fired tankless water heaters are usually around 30 x 20 inches and require proper venting space to release fumes to prevent combustion. If you don’t have space, an electric unit would be a better choice.

Rheem RTGH-95DVLN Tankless Natural Gas Water Heater


Cold Water Temperature

Before you purchase any water heater, be sure to measure your running water’s temperature. Tankless water heaters don’t store water in a tank, so it should be capable of heating up water to your desired specification. For instance, hot water for use in a kitchen should reach around 120° F, so cold water is about 50° F, then the tankless water heater should heat it up 70° F while it’s running at its maximum flow rate.

Check Your Water Flow Rates

Your home’s water flow rate measures the efficiency of a tankless water heater. Low-flow showerheads and sinks may have a maximum flow rate of 1.5 gallons-per-minute (GPM), whereas a bathtub might go up to 4 GPM. When purchasing appliances, check to see if they have a GPM rating. If not, you can measure the GPM yourself by placing a 1-gallon jug or container beneath its faucet and counting how long it takes for the jug or container to reach full capacity. If it takes 20 seconds, then it has 3 GPM rating (3 gallons every 60 seconds).

Takagi T-KJr2-IN-LP Indoor Tankless Water Heater

Takagi T-KJr2-IN-LP

Significance of BTU

The British Thermal Unit (BTU) measures how efficient a water heater is at heating water every hour. For example, a 140,000 gas tankless water heater should heat up 140,000 pounds of water by 1° F every hour.

This same heater unit should also heat water up to 1,400 pounds of water by 100° F every hour. Essentially, BTU measures the recovery rate in which the unit heats water up to its desired temperature. The higher the BTU, the more time-efficient it is in heating up your water.

Which Tankless Gas Water Heater to Get

As we mentioned earlier, there are a large number of tankless water heaters that draw energy from natural gas or propane. The only question left to answer is which model performs bestHere, we will provide you with our pick of the top five tankless gas water heaters.

Rinnai V65IN Tankless Natural Gas Water Heater

Rinnai V65IN

Our Recommended Indoor Tankless Gas Water Heaters in 2021

5) Rinnai RUC98iN Tankless Water Heater

The fifth spot goes to Rinnai’s RUC98iN. This remote-controlled (RC included) unit is only 18.5 x 26 x 10 inches, so it takes up very little space, allowing you to allocate more of your homes remaining space for venting purposes. This Energy Star-certified heater has a maximum GPM rating of 9.8 GPM and can heat up your home water to up to 140° F. Depending on how often you use warm and hot water in your home, and you can adjust the RUC98iN’s BTU-count from between 15,200 and 199,000.

Apparently, the higher the BTU you use, the higher your gas bill. The only problem with this unit is that it takes a few seconds for it to deliver adequately heated water, so you’re sending several gallons of cold and lukewarm water down the drain.

Rinnai RUC98iN Ultra Series Indoor Natural Gas...
  • INDOOR installation only. Fuel Type: NATURAL GAS.
  • Concentric or PVC venting option
  • Up to 0.96 Energy Factor/Up to 0.92 Uniform Energy Factor

4) Rheem RTGH-95DVLN Tankless Natural Gas Water Heater

The next item on our list is the RTGH-95DVLN by Rheem. This unit is another space-saver, measuring only 18.5 x 9.8 x 27 inches.

This model has a 9.5 GPM rating which is much more than the average household will reasonably need. Like the previous model, this one also has a maximum heating capacity of up to 140°, though it may not be able to deliver a constant flow of 140°-water at all times.

However, it performs flawlessly for water temperatures up to 120°. The RTGH-95DVLN also comes with an adjustable BTU setting (can be configured using the remote control) of between 11,000 and 199,900 BTU. Another drawback of this model is that it’s needlessly loud, so be sure to place the unit in a well-ventilated basement to drown out the hammering sounds it produces.

Rheem RTGH-95DVLN 9.5 GPM Indoor Direct Vent...
  • 94-Percent Energy efficient with stainless-steel condensing heat exchanger
  • Intelligent electronic controls designed to increase energy efficiency and safety
  • Third party efficiency listed by AHRI

3) Takagi T-KJr2-IN-LP Indoor Tankless Water Heater

The Takagi T-KJr2-IN-LP gas-fired tankless water heater is another Energy Star-certified appliance. It delivers up to 6.6 GPM of heated water from low-temperature (around 50° F) at a consistent rate, though most small- to medium-sized households will find the max GPM to be borderline sufficient. It can provide water up to 165° F without any troubles and almost instantly.

Using the remote control, you can adjust the BTU settings from between 19,500 and 140,000 BTU. It’s also whisper-quiet, so there’s virtually no risk of hearing and loud noises coming from the unit, even when it’s working at almost full capacity. The T-KJr2-IN-LP takes only 6.7 x 13.8 x 20 inches of space and can be mounted easily.

Takagi T-KJr2-IN-LP Indoor Tankless Water Heater
  • Maximum BTUs: 140,000 ; Minimum BTUs: 19,500
  • Vent Type: Direct Vent ; Water Connection Location: Bottom ; Water Connection: 3/4 Inch
  • Heat Exchanger: Copper; Voltage: AC 120V ; UEF: 0.80 ;Emissions: Low Nox

2) Rinnai V65IN Tankless Natural Gas Water Heater

The V65IN by Rinnai is an Energy Star-rated gas-fired on-demand water heater that measures only 8.8 x 13.88 x 23.6 inches, allowing you to use a tremendous amount of room space for ventilation.

It has a 6.6 GPM rating, though, for sufficiently hot water (up to 140° F for this unit), it’ll only provide up to 4 GPM – still enough for running multiples hot water faucets in apartments and small homes.

This model has an adjustable BTU-count of between 10,300 and 150,000 BTU. All adjustments of this model can be made using the remote controller (included in the kit). Even while running at full capacity, the V65IN is reasonably quiet. However, there might be some confusion regarding installation, and the manual won’t be of much help.

Rinnai Indoor Tankless Hot Water Heater / V65iN /...
  • Up to 6.5 GPM hot water flow rate (varies by groundwater temp)
  • Control-R 2.0 mobile app features timers and schedules throughout the day and allows you to remotely put the...
  • Residential Factory Warranty - 120 months (heat exchanger), 12 months (labor), 60 months (parts)

1) Takagi T-KJr2-IN-NG Indoor Tankless Water Heater

The gas tankless water heater model that takes home the crown is the Takagi T-KJrN-IN-NG. This Energy Star-certified water heater measures in at 13.8 x 6.7 x 20.3 inches, making it extremely compact and easy to mount. Its BTU-rating range is between 19,500 and 140,000. It has a maximum GPM capacity of up to 6.6 GPM for up to 160° F water, making it the most reliable and sufficient model.

The quick recovery rate of this model allows it to heat up water in large apartments and homes adequately. However, some users have expressed their dissatisfaction with the T-KJr2-IN-NG for its inability to provide hot or even warm water in low flow rates (up to 1.9 GPM). You’ll need to have a flow rate of at least 2 GPM to get the unit running correctly.

Takagi T-KJr2-IN-NG Indoor Tankless Water Heater,...
  • 140,000 BTU. Voltage: AC 120V
  • 6.6 GPM max flow rate. Water connection location- bottom
  • 4-Inch category III stainless steel venting required


A tankless water heater is much more efficient than the traditional tank heaters. Essentially, tankless heaters heat up your water as it’s drawn, meaning that it only heats up what you use. Conventional models for residential use have to reheat stored water that hasn’t been used, causing a spike in your electric or gas bills. Tankless water heaters, like their traditional counterparts, can either be gas-fired or electric-powered.

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

Takagi T-KJr2-IN-NG

Before purchasing a gas heater, it’s important to determine how much water you need per hour or day since this let you know how big or strong of a gas water heater you need. The more hot water you use, the more powerful a unit you need.

You can check your hourly or daily hot water usage by looking at your appliances or using simple online calculators to give you a rough estimate. After knowing how much hot water you use regularly, then you can start looking at the specs of each tankless water heater model (GPM rating and BTU rating, as well as the unit’s size and weight).

Rinnai RUC98iN Tankless Water Heater

Rinnai RUC98iN

In this article, we’ve given you our pick for the top 5 home-use gas-fired tankless water heater. We placed Takagi’s T-KJr2-IN-NG at the top mainly for its excellent efficiency at providing 6.6 GPM of 140° F water at a consistent rate.

Though there’s a waiting period before turning your hot water faucet and receiving hot water, the delay is considerably shorter than what you’d get with the other four models.

Its large BTU range allows the user to determine how gas to use to heat the incoming flow of water efficiently. The only drawback is that it somewhat underperforms when drawing low water flow rates (up to 1.9 GPM). You’ll need a water flow of at least 2 GPM to get properly uninterrupted heated water.

Indoor Tankless Gas Water Heater | Bestseller

SaleBestseller No. 1
Rinnai Tankless Hot Water Heater / V75IN / Natural...
Rinnai Tankless Hot Water Heater / V75IN / Natural...
Up to 7.5 GPM hot water flow rate (varies by groundwater temp)



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Indoor Tankless Gas Water Heaters
Indoor Tankless Gas Water Heaters
Indoor Tankless Gas Water Heaters
Indoor Tankless Gas Water Heaters
Indoor Tankless Gas Water Heaters
Indoor Tankless Gas Water Heaters

Last update on 2021-06-21 / Most affiliate links and/or Images from Amazon Product Advertising API

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