Best Indoor Tankless Water Heater For Small Home [Updated]

Buyers Guide, Tankless Water Heater

indoor tankless water heater
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Are you on the lookout for an unbiased review of the best indoor tankless water heaters?

Well, in this post, I would be walking you through some of the best indoor tankless water heaters in order to help you make an informed buying decision.

Moreover, I would also be throwing light on some of the “must-have” parameters when it comes to buying an indoor tankless heater.

Lastly, I would be responding to the queries related to the tankless heater review in order to help you clear most of your doubts if not all.

But, before that, I would be needing a small help on your end.

Would you be interested in helping me?

Well, if your answer is “YES”, then all you need to do is to respond to a couple of questions that I would be asking in a while.

Does it make sense?

So, which is your favorite tankless heater brand?

How often do you read product reviews?

Moreover, how much are you willing to spend on your favorite tankless heater?

Enough of questions, right?

So, without any further ado, let’s begin…

Top 7 Best Indoor Tankless Water Heaters Comparison Chart

Frankly speaking, it wasn’t an easy task to shortlist the indoor heaters for review as the market is flooded with a wide range of tankless brands and models.

So, I think and believe that you should be made aware of our shortlisting process in order to maintain a high level of transparency.

First and foremost, my core team does the brainstorming to come up with a set of parameters on which the products need to be evaluated.

In this case, the product is an indoor tankless heater.

Secondly, each evaluating parameter is assigned a certain weightage depending upon its ability to influence buyers’ decisions.

During the evaluation process, each and every product gets a certain score depending upon its performance.

Finally, we sum up the score and shortlist the “top ten” scorers for reviewing.

In case, you’ve any doubts or queries related to our review process, then feel free to reach out to us.

Check the current price of the product on Amazon by clicking the link.

Indoor Tankless Water Heaters  TypeMaximum GPM(Depth, Height, Weight) in Inches Weight (LBS) 
Stiebel Eltron DHC- E 12 Electric 4.5 GPM4.1 * 14.25 * 7.9 6 lbs
EcoSmart ECO 27 Electric 6.5 GPM3.625 * 17 * 1714.7 lbs
Stiebel Eltron Tempra Plus 29 kW Electric  6 GPM4.6 * 16.6 * 14.517.6 lbs
Rheem RTEX-36 Electric  8.8 GPM3.5 * 18.25 * 21.6322.7 lbs
Rheem RTGH- 95 DVLNNatural Gas/Propane9.5 GPM9.88 * 25.63 * 13.8879 lbs
Rheem Prestige SeriesNatural Gas/Propane11 GPM14.8 * 17.3 * 28.785 lbs
Rinnai RUR 199Natural Gas/Propane 11 GPM12 * 27.9 * 18.5 73 lbs

Which is the best indoor tankless water heater for small home?

Frankly speaking, the market is flooded with good quality indoor tankless water heaters, and naming one as the “best” indoor tankless wouldn’t be fair.

However, as per my knowledge, experience, and feedback from my clients, I can affirm that Stiebel Eltron 230628 is definitely the one that I would recommend as the preferred option.

Definitely, the unit is simple, reliable, and can provide hot water right at the sink without any hassle.

The unit is small, compact, and sleek designed to fit even in the small space effortlessly.

DHC can easily deliver warm or hot water to a single point of use, usually a hand wash or utility sink.

As compared to a conventional heater, the little beast is known to consume 50 percent less power.

I really liked the fact that the unit performs quietly and the credit goes to hydraulic control which is definitely something to boast about, isn’t it?

Furthermore, resettable safety high limit switch would be of great help when it comes to dealing with an unprecedented situation.

And, you know what, the unit is available in a wide range of kW sizes for a variety of single-sink applications in order to help you achieve optimum results effortlessly.

Since the heating element present in the device is controlled by a flow switch which simply means that DHC can never dry-fire and fail prematurely.

Many of you wouldn’t be aware of the fact that DHC water heaters are equipped with a safety high limit with a manual reset.

Not only does it possesses seismic proof construction but also is equipped with self-modulating technology.

In fact, the advanced microprocessor controls provide you with better control over the device.

The 6 lbs DHC-E12 has a flow rate of 1.5 gallons per minute and the operating temperature falls in the range of 86 and 125 degrees Fahrenheit.

Lastly, the unit is backed by three years of warranty on parts which clearly depicts the trust and confidence of the manufacturer in its offering.


  • One of the cheapest option on our list
  • Smallest and lightest
  • Definitely, one of the best options on our list for small homes and point of use situations
  • Self-modulating and advanced microprocessor controls
  • Seismic proof construction and no scalding
  • Up to 50 percent less power consumption
  • 3 years warranty on parts


  • Unfortunately, the unit doesn’t have the best GPM flow rate on our list

Top 10 Best Indoor Tankless Water Heaters Review

Frankly speaking, the world of tankless water heaters is not only expansive but also impressive.

And, this goes with almost all the models including indoor ones.

So, without wasting any time, let’s have an in-depth discussion on each one of them.

EcoSmart ECO 27 Electric Tankless Water Heater

So, here I come with one of my favorite indoor tankless heaters on the list.

Trust me, the EcoSmart ECO 27 comprises almost all the essential ingredients that you might be looking for in your indoor electric tankless heater.

Furthermore, EcoSmart ECO 27 is a 27-kilowatt tankless electric water heater that can easily suffice the hot water requirements of apartments, condominiums, townhomes, etc.

In short, you don’t have to worry at all if you’re planning to buy this unit for whole-home applications.

Depending upon the incoming underground water temperature, the unit can help you with the flow rate in the range of 2.7 and 6.5 gallons per minute.

On top of it, the unit is equipped with self-modulating flow sensor technology that plays a crucial role in regulating the amount of energy required to heat the water needed.

Many of you wouldn’t be aware of the fact that the ECO 27 is the largest electric tankless heater on our list available with patented self-modulating technology.

Furthermore, if you’re a resident of the northern USA, Canada, and Southern State, then definitely, the ECO 27 is for you.

The device is equipped with a digital temperature control feature that allows you to set the temperature in the increment of 1-degree.

As compared to the conventional tank-style heaters, the ECO 27 claims to save up to 90 percent storage space.

Since the unit is an electric tankless model so the standby heat loss is almost negligible.

Not only is the ECO 27 99.8% energy efficient but also UL and CSA certified.

Lastly, the 11 lbs ECO 27 is backed by a lifetime warranty on electronics, exchangers, and elements.


  • ECO 27 is the best budget option for medium-sized homes
  • It is not only powerful but also possesses maximum GPM for a low price
  • Smallest and lightest option for those who are looking for medium-sized homes
  • Lifetime warranty on electronics, exchanger, and element
  • UL and CSA certified
  • The unit is equipped with patented self-modulating technology
  • 99.8 percent energy efficient


  • Doesn’t comes with Wi-Fi capability
  • Might not be the best choice for the extreme colder climates

Stiebel Eltron Tempra Plus 29 kW

The Stiebel Eltron Tempra Plus 29 is a whole house electric tankless water heater made in Germany.

Stiebel Eltron is a well-established brand that has proved its mettle time and again.

The brand is known for both innovative and affordable offerings and claims to be a world leader in hot water technology.

Whether you’re a first-time buyer or a seasoned professional, you’ll not find any problem when it comes to installation as the unit doesn’t require venting.

On top of it, the Stiebel Eltron Tempra Plus 29 operates quietly and can be installed in small spaces because of its compact and sleek design.

Of course, the electric tankless mitigate the standby heat loss problem resulting in a tangible saving on your electricity bills.

Moreover, the unit boasts of being 99 percent energy-efficient.

The solid copper heating chambers and advanced flow control contribute to enhanced efficiency and performance.

With the help of a digital temperature display, you can keep track of the temperature.

The enhanced auto modulation technology contributes to energy saving.

Frankly speaking, the advanced flow control could be of great help when the demand for hot water exceeds capacity.

What actually the technology does is, reduces the water flow slightly in order to maintain a consistent temperature.

Lastly, the unit is backed by 7 years warranty on leakage and 3 years on parts.


  • 7 years warranty on leakage and 3 years on parts
  • Performs relatively better in cold climatic conditions
  • Equipped with advanced and innovative technology
  • An affordable indoor tankless water heater
  • Small, compact, durable, and reliable
  • Best electric tankless for medium-sized homes


  • Not the most powerful indoor tankless on the list and also lacks Wi-Fi capability

Rinnai RL75IP RRL75iP

The Rinnai RL75IP RRL75iP is definitely one of my favorite models from the brand Rinnai.

Needless to say, the heater is equipped with almost all the essential features that you might be looking for in your favorite indoor tankless heater.

Definitely, the on-demand hot water heater is powerful and can help you with a flow rate of up to 7.5 GPM.

Furthermore, the Rinnai heater is equipped with Circ-Logic technology that allows you to set recirculation patterns that coincide with your typical habits.

The hot water heater is uniquely designed to be installed in non-tradition spaces such as the attic, closet, etc.

Since the heater heats water only when it is required so you don’t have to deal with any standby heat losses, and as a result, you can expect the unit to use up to 40 less energy for heating which is definitely something to brag about, isn’t it?

The Rinnai tankless is equipped with Wi-Fi monitoring that will not only monitor the efficiency of the tankless heater but also address the issues in advance in order to help you with uninterrupted service.

Moreover, most of the parts are replaceable so you don’t have to buy a new unit for silly malfunctioning.

As compared to a traditional heater, the Rinnai tankless will last almost twice (20 years).

In simple words, premium heaters such as Rinnai will definitely save you both time and money in the long run.

The Rinnai RL75IP Indoor Tankless Hot Water Heater uses liquid propane as fuel and is ideal for two to three bedrooms.

The 50 lbs RL75iP is energy star certified and can be mounted virtually in any room.

Lastly, the unit is backed by 10 years warranty on heat exchanger, 5 years on parts, and 1 year on labor.


  • One of the best propane-fueled indoor heaters for medium-sized homes
  • One of the highest GPMs on our list
  • Circ-Logic capability
  • Control-R Wi-Fi capable
  • Smart, compact, sleek designed
  • 10 years warranty on heat exchanger


  • Most expensive option among medium-sized home units

Ecosmart ECO 36 36kw 240V Electric Tankless Water Heater

To begin with, EcoSmart ECO 36 is an electric tankless water heater that claims to be 99.8 percent energy-efficient.

Moreover, the EcoSmart ECO 36 is a 36-kilowatt tankless electric water heater ideal for catering to the hot water requirements of apartments, townhomes, and other whole-house applications.

Furthermore, the unit is powerful and can provide a flow rate of up to 8.7 GPM depending upon the temperature of incoming groundwater.

In fact, the EcoSmart ECO 36 is the most powerful heater in the ECO series and can help you with an unlimited hot water supply.

Even in the areas such as the Northern United States wherein incoming water temperature can reach as low as 37 degrees Fahrenheit, the ECO 36 is capable of providing a flow rate of 3.7 GPM making it highly suitable for low-temperature belts.

You can easily understand the capacity of this unit from the fact that it is capable of providing hot water to up to 4 showers and 1 sink simultaneously.

Even in the coldest climatic conditions, the ECO 36 is capable of handling up to two showers simultaneously.

The unit is also equipped with digital temperature control that allows you to set the temperature of the device in the increment of 1 degree.

Lastly, the 18 lbs ECO 36 is backed by a limited lifetime warranty which clearly depicts the confidence and trust of the manufacturer in its offering.


  • The best budget electric indoor tankless for large homes and cold climatic conditions
  • Lightest and smallest option for larger homes
  • Fairly powerful and capable of providing hot water to 2 showers simultaneously in the extreme climatic conditions


  • No Wi-Fi capability

Rheem 240V 4 Heating Chambers RTEX-36 Residential Tankless Water Heater

So, here I come with yet another highly powerful indoor residential tankless water heater that is equipped with advanced technologies and idiosyncratic features in order to help achieve an optimum result.

The unit is equipped with the most advanced modulation technology that adjusts power in the best possible manner in order to cope up with hot water demand.

Also, the unit possesses external digital thermostatic control along with an LED display.

The installation process is simple and easy and doesn’t take much time.

The digital temperature display will help you in reading the temperature without any error.

Furthermore, the Rheem RTEX-36 (240V) will provide 2.5 GPM at a 98 degree F temperature rise and 6 GPM at a 30 degree F temperature rise.

You can set the temperature of the indoor heater in the range of 80-140 degrees Fahrenheit with a one-degree increment.

The device comprises four chambers and each one of them requires a 40 amp breaker.

In the warm climatic conditions, you can expect it to serve hot water to a couple of faucets and showers simultaneously which is definitely sufficient even for a larger home, isn’t it?

All in all, one of the best electric indoor heaters for larger homes.


  • One of the most powerful indoor electric heaters on our list
  • Equipped with advanced technology
  • An affordable option among the larger home options
  • Small, compact, and lightweight


  • One of the widest of all the units that made to our list

Rheem RTGH-95DVLN-2 Tankless Water Heater

The Rheem Prestige® RTGH-95DVLN-2 is a natural gas indoor tankless water heater that comes with industry-leading low flow activation with a minimum flow rate of  .26GPM and minimum activation flow rate of .40GPM.

As a result, you can expect to receive hot water even in low-demand conditions.

Moreover, the Ultra-Low NOx burner meets the SCAQMD rule requirements of safety with low emissions.

The manufacturer boasts about saving up to 11,000 GPM with the help of water-saving technology that the unit is equipped with.

Also, the unit comes with Hot Start Programming that plays a crucial role in minimizing cold water bursts by staying in a ready-fire state.

Frankly speaking, with 199, 900 BTU the device is powerful enough to suffice the hot water requirements of 3 bathrooms and 2 kitchens.

Even though the installation is simple and straightforward still I would suggest you take the help of a certified professional in case, you’re a first-time buyer and don’t have prior experience of plumbing.

During the installation process, some of my clients have faced the problem of routing the condensate drain line.

The 77 lbs energy star certified can be easily wall-mounted to free the floor space for other more important tasks.

Lastly, the indoor water heater is backed by 12 years warranty on heat exchanger, 5 years on parts, and a year on labor.

However, to avail of the warranty and prevent it from becoming void, professional installation is a MUST.


  • Wi-Fi Capability
  • Works great at higher altitude
  • An affordable option in the natural gas/propane indoor tankless heater category
  • Backed by longer duration of the warranty
  • Powerful, compact, and highly energy efficient


  • Wi-Fi isn’t automatically pre-installed

Rheem RTGH-RH10DVLN Prestige Series Professional Condensing Tankless Gas Water Heaters

Well, the Rheem Prestige RTGH is a highly efficient condensing tankless water heater designed for high water demands.

The Rheem Prestige® RTGH-RH10DVLN-2 comprises a built-in recirculation pump with auto-learning programming that helps you with instant hot water supply whenever you need it.

On top of it, the ultra-low NOx burner meets SCAQMD rule requirements of safety for low emission so you can consider the unit to be environment friendly.

It is also equipped with a gas and water leakage detector in order to prevent any last-hour misadventure.

As the name suggests, the overheat cut-off switch will prevent overheating of the device by cutting off the supply whenever the temperature will touch the upper acceptable limit.

Some other safety features include exhaust and water temperature sensors, flame sensors, etc.

Again, the number of bathrooms that can be put to use to a large extent depends upon the incoming groundwater temperature.

In a warmer climate, you can expect this unit to serve up to 5 bathrooms simultaneously.

In fact, the unit is capable of providing up to 11 GPM which is definitely something to boast about.

If I’m not wrong then the unit is capable enough to cater to the hot water requirements of a larger home effortlessly.

The installation process is simple, quick, and hassle-free.

In fact, the built-in pump saves a lot of time on installation.

The unit is also equipped with programmable time-based activation in order to help you reap maximum benefits from the innovative and advanced features with ease.

Lastly, the 85 lbs unit is backed by 12 years warranty on heat exchanger, 5 years on parts, and a year on labor.


  • Capable of providing flow rate up to 11 GPM
  • Equipped with safety features including a flame sensor, overheat cut off switch, gas and water leak detectors
  • The minimum activation flow rate of .50GPM
  • Longer duration of the warranty


  • Expensive

Rinnai RU199iN RRU199iN, RU199in-Natural

The Rinnai RU199iN uses natural gas as a fuel and is suitable for mid to large-sized homes’ hot water requirements.

The unit is capable of providing a flow rate of up to 11 GPM depending upon the incoming groundwater temperature.

On top of it, the circ-logic technology allows you to set recirculation patterns that coincide with your typical habits.

In layman’s terms, hot water is available whenever you need it.

Compact and unique design makes it possible to get installed even in non-traditional areas including attic and closet.

Since the unit uses energy for heating water only when you need it so you can expect it to use up to 40 percent less energy as compared to a traditional water heater which is definitely something to brag about, isn’t it?

Wi-Fi monitoring keeps a track of the heater performance and deals with the issues in advance in order to prevent any disruption or last-hour misadventure in the service.

The average life expectancy is 20 years which is almost twice of any traditional hot water heater.

Furthermore, the 64 lbs RU199iN can be wall-mounted to free the floor space for other important tasks.

In one sentence if I’ve to explain this product, then all I’ll say is easy to install and comes with almost everything required.


  • One of the most powerful options on our list for sure
  • Bound to save you both money and energy in the long-run for sure
  • Circ-Logic capable
  • Wi-Fi capability


  • Recirculation isn’t automatically pre-installed

Rinnai RUR199iP RRUR199iP, RUR199ip-Propane

To be honest, the RUR is the best Rinnai series for sure.

And, in the RUR series, the RUR199 is definitely one of the most powerful options if not the POWERFUL.

In simple words, the RUR199iP is a premium offering from the brand Rinnai and of course, for good reasons.

The unit is equipped with almost all the essential ingredients that you might be looking for in a powerful indoor water heater.

In fact, the brand boasts of delivery up to 11 GPM.

With the BTUs falling in the range of 15, 000 and 199, 000, the unit is bound to deliver high-performance.

Not only the unit is energy-star certified but also possesses a consistent UEF of 0.93.

You don’t need any extra add-ons as the unit is equipped with innovative technologies including Circ-Logic Capability and Control-R Wi-Fi Capability.

Trust me, you’ve already got the best recirculation as well as the ability to control, all from a tablet or a phone.


  • Wi-Fi is automatically pre-installed
  • Circ-Logic capable
  • Equipped with recirculation technology
  • Powerful and energy-efficient
  • A premium offering from the brand Rinnai


  • Expensive

Indoor Tankless Water Heater Buying Guide

It’s my humble request to both the newbies and the experienced buyers to NOT SKIP this section.

We’ve tried to the best of our capabilities to come up with this comprehensive buying guide wherein we’ve discussed almost everything related to indoor tankless heaters that we could.

Indoor Tankless Water Heater vs Outdoor: Which One Should I Buy?

Well, if you’re a first-time buyer or even a seasoned professional, you might be inquisitive about which one should you opt for, right?

When it comes to selecting a tankless heater, there are two things that you must be clear with.

  • Type of fuel, that is, gas or electric
  • Type of installation, that is, indoor or outdoor

Honestly speaking, both indoor tankless and outdoor have their own shares of pros and cons that we would be discussing in a while.

Rather than, coming up with a lengthy explanation what we thought is to come up with a tabular format that will possess almost all the essential pieces of information related to the topic.

  Indoor Installation Outdoor Installation
 Cold Climatic Condtions Winner 
Lack Set Up for Indoor Gas Heater  Winner
 Poor Interior Drainage  Winner
 Newly Constructed Homes Winner 
 Scarcity of Space  Winner
 Less Spending Per Unit Winner 
 Quiet Operation  Winner
 Vandalism Threat Winner 
 High Risk of Power Outages Winner 
Multiple Point of Use HeatersWinner

I’ve done my work and now it’s your turn to decide which one syncs well with your requirements.

How to choose between gas and electric indoor water heaters?

It is quite possible that you don’t have access to both types of fuels, so in that case, the selection is easy as you’ll go with the one that is accessible, right?

What if, both types of fuels are accessible in abundance?

Whole House/Point of Use

You need to figure out whether you want to go for the whole house or the point of use heater.

If you’re looking for a whole house water heater then definitely, indoor gas heaters would be a better option.

The indoor gas heaters are meant to have higher GPM which means they can provide hot water to multiple appliances simultaneously.

On the other hand, electric indoor heaters are a perfect fit for small homes with lower hot water demands.

Point-of-Use heaters are perfect for showers and hot tubs.

In case, you’re looking for an indoor heater for your sink which is far away from the centralized heating system, then try these under sink heaters, they are worth the investment.

Don’t forget to compare the tankless water heaters cost

To be honest, the operating cost of an indoor gas tankless heater is far less as compared to the electric counterparts.

But, at the same time, I can’t deny the fact that the fuel price can change drastically in the future.

Also, different regions have different prices for both fuels, so don’t forget to check their prices in your locality.

An electric indoor heater can be cheap if you’re using solar panels on your roof.

However, the upfront cost of an indoor gas heater tends to be on a higher side which might be a point of concern in case, you’re on a shoestring budget.

To sum up, the purchase price, as well as installation cost for an indoor gas heater, is always higher than an electric counterpart.

Since an indoor gas heater requires ventilation so the price is bound to be on the higher side.

All you need to understand is, an indoor gas heater will pay you in the long run but will be more expensive in the short run.

Look for the environmentally friendly option…

Many of you wouldn’t be aware of the fact that electric heaters are more environmentally friendly as compared to their gas counterparts.

Moreover, my clients have shown more interest in electric heaters as they don’t directly emit co2.

Definitely, lack of co2 emission is an added advantage for sure.

Even the maintenance required for an electric indoor tankless heater is far less than the gas counterpart.

To sum up, both have their own share of pros and cons and depending upon your budget and requirements, you can choose one.

How to select the right size and right type of indoor tankless heater?

Frankly speaking, just reading the aforementioned comparison chart wouldn’t be sufficient to come to a conclusion, right?

You need to be thorough with quite a few questions including what GPM do you require, what about the temperature rise, etc?

Moving further, I’ll try to the best of my capabilities to help you find out the right type of indoor tankless heater.

Determine the flow rate that you need

As discussed earlier, the flow rate of an indoor tankless heater is measured as Gallons Per Minute.

Finding the amount of flow rate that you need isn’t difficult at all.

All you need to do is to add up the flow rate of all the appliances that you want to run for hot water.

For example, bathroom and kitchen sinks require only about 0.5 GPM.

Next, you’ve got the dishwasher at 1.0 GPM which is almost twice that of sinks.

On the other hand, the GPM requirement of a washing machine is approximately 1.5 GPM.

Of course, showers GPM are on higher-end somewhere around 2.5 GPM.

However, you can drastically reduce the GPM requirement of your shower to just 1.5 GPM by simply using a low-flow shower.

Appliances  Flow Rate (GPM)
 Bathroom Faucet 0.5 GPM
 Kitchen Faucet 0.5 GPM
 Shower  2.5 GPM
 Dishwasher  1.0 GPM
 Clothes Washer  1.5 GPM

So, what you need to do is to consider how many of your appliances you’ll likely want to use simultaneously.

Add them together to pick up the appropriate flow rate of your heater.

There is another way to find the average GPM for your home.

For example, an apartment or condo with a single bathroom will be needing on average a hot water heater of 3.0 GPM.

On the other hand, a 4.0 GPM would suffice the hot water requirement of houses less than 1000 square feet.

An average-sized home somewhere in the range of 1,000 and 1,600 square feet with two bathrooms would require a residential tankless heater with a GPM not less than 7.5.

Similarly, houses with more than 1600 square feet consisting of 3 or more bathrooms would be requiring a GPM of close to 10.

However, the above calculation is only valid if you’ve got the local water temperature of at least 67 degrees Fahrenheit.

In case, the temperature of the incoming groundwater falls below this benchmark then you would be needing a higher GPM.

Pick up the right temperature rise capability

Frankly speaking, your local water supply impacts the temperature rise you require.

In a warmer climate, the local water supply can be as high as 77 degrees Fahrenheit.

On the contrary, in the north of the US, the incoming groundwater temperature can go as low as 35 degrees Fahrenheit.

In fact, the incoming water temperature can also have an impact on how long it takes for your water heater to heat up.

In order to find out the temperature rise you require, you need to consider the ideal temperature for different appliances.

For example, a shower is comfortable at between 102 and 105 degrees Fahrenheit.

Similarly, a kitchen sink would be needing somewhere around 110 degrees Fahrenheit.


If that is the case, then please allow me to explain the concept with the help of a couple of examples.

Example 1: One Bathroom, Hot Climate

As discussed earlier, a tankless heater with one bathroom and one kitchen sink, a single shower, and a dishwasher, and no washing machine would be required to offer 4.0 GPM.

A lower GPM would do the trick if you would be running a lesser number of appliances.

Let’s assume that the home is in a warmer climate where the incoming water temperature is 75 degrees Fahrenheit.

In such scenarios, you would only be needing a temperature of 35-degrees Fahrenheit, and as a result, you can pick up any of the indoor tankless models from our review.

Example 2: Two Bathrooms, Average Climates

The second example that I’ve got for you is the average-sized homes with two bathrooms.

Assuming that such apartments have two bathroom sinks, two showers, one kitchen sink, a dishwasher, and a washing machine.

A tankless water heater for a 2-bathroom house would be needing somewhere around a GPM of 8.5 in case, you want to run all the appliances simultaneously.

But, if you’re not gonna run all the appliances simultaneously then even a 7.5 GPM would do the trick for you.

The other parameter that you need to consider is none other than the temperature rise.

To provide hot water in an average climate (considering incoming water temperature to be somewhere around 54 degrees Fahrenheit), the water heater would be needing a temperature rise of at least 48 degrees Fahrenheit.

Example 3: Three Bathrooms, Cold Climates

So, here I come with my last example wherein I would be considering a large-sized home.

Suppose you own four bedrooms apartment that comes with three bathrooms, and an in-law suite.

Also, assuming that your home is having three showers, three-bathroom sinks, two kitchen sinks, two dishwashers, and two machines.

Huge list of appliances, right?

In order to figure out the right GPM for your tankless heater, you need to decide on the number of appliances that you’re likely to use simultaneously.

A GPM of 10 would do the trick for you.

Either you can opt for multiple point-of-use electric heaters or you can consider high-powered gas models.

And, if your apartment resides in a colder zone, then in order to manage the cold climate, an instant-on water heater would be needing the highest possible temperature rise.

Assuming the incoming water is 47-degrees Fahrenheit, the heater would be needing a 60-degree Fahrenheit temperature rise, right?

At the same time, it would be utterly important to keep receiving close to the maximum GPM, as the GPM a heater is able to supply is lower when it needs to heat water to a greater extent.


If you can afford then it’s always good to have an indoor tankless heater equipped with recirculation technology.

The units with a recirculation system are designed to loop any cold water standing in the hot-water lined back to the unit.

Such a system includes a high-quality and efficient pump that is known to push water through a dedicated return line to the heater.

The best thing about the recirculation technology is that it almost negates the wait time, and helps in providing the hot water instantly.


Always look for indoor tankless units that come with at least a couple of years of warranty.

In simple words, the longer the warranty period the better it is.

At the same time, you also need to keep in mind that certain indoor tankless unit is eligible for warranty only when the installation is done by a certified professional.


Needless to say, pricing is definitely an important influencing factor when it comes to buying an indoor tankless unit.

Moreover, if you’re a first-time buyer, then please refrain from impulse buying rather than read some product reviews and do some homework before making a final buying decision.

Trust me, I’m a part of this industry for over a decade now, and with my knowledge and experience, I can affirm that costliest isn’t always the best, and the cheapest isn’t always the worst.

Indoor Tankless Water Heater Installation Tips

I hope the information that I’m gonna share with you in a while would definitely help you in the installation process by reducing the efforts and hassle.

Mounting Tips

Frankly speaking, an exterior wall is definitely one of the best places for the installation of indoor tankless heaters.

By doing so, venting and unit installation becomes easier and cheaper.

Even though you’re a first-time buyer mounting the heater and securing it to the wall wouldn’t be a tedious task for you.

All you require is a couple of screws at the top and the bottom, that’s all.

For the best result, you can exploit the crossbeam present behind the drywall for mounting the heater.

Since the structure is strong so it is able to provide excellent support.

Even directing the vent above as well as through the wall wouldn’t be a hassle for you.

If the aforementioned method didn’t fascinate you, then you can install a piece of plywood between two vertical studs and mount the heater to the plywood.

Proper Clearance

If you’re installing an indoor tankless heater that requires venting then you need to maintain proper clearance from any doors, windows, plants, or air intakes, or exhausts from other appliances.

As an educated installer, you must consult both the manufacturer’s instructions and local codes.

Don’t take clearance lightly as it helps in getting indoor tankless heaters sufficient air supply.

And, also, helps in moving the flue gases out without compromising on safety.

Depending upon the model you choose, you can find the required information in the users’ manual.

However, as a thumb rule, it is one foot from front and bottom, and half an inch on the sides.

Power Vent vs. Direct Vent

I always prefer the models that come with a power vent, and there is a simple reason for it.

Yes, you guessed it correctly.

Indoor tankless hot water heaters that come with a power vent system are meant to be more flexible as compared to direct vent models as the latter’s vent pipe can be very long even 50 feet or longer.

You need to understand that for the proper venting, it is highly recommended that you’ve pipes that are as short as possible.

Also, you need to ensure that it doesn’t exceed the recommended number of venting pipe fittings.

Vent Kit

Well, tankless water heaters usually come with the installation vent kit which makes the installation less time-consuming and hassle-free.

Moreover, based on the indoor tankless water heater’s venting configuration additional venting components might be needed.

Also, you need to secure and seal all the joints perfectly to prevent any last-hour misadventure.

Horizontal vs Vertical Termination

To be honest, depending upon the location and availability of space, the unit can be either vented horizontally through the sidewall or vertically through the roof.

If I’m not wrong then most of the tankless water heaters have either 3″ or 4″ vents.

In fact, vertical vent pipes should terminate with the roof flashing and rain protection.

Condensing vs. Non-Condensing

If the heater is non-condensing, then you need a stainless steel vent because of the acidic condensate and the high temperature of the flue gases.

You might be needing a condensate trap in case of vent pipe being too long.

On the other hand, condensing models don’t require this type of pipe.

In fact, these can use PVS, ABS, or something similar but it should be according to the manual.

Things to consider

  • Vent pipe installation
  • Location of the gas, electricity, and water supply line
  • Also, the location of the most used hot water fixture
  • Available space such as closet, bathroom, etc
  • Required tools: power drill, hacksaw, level, screwdriver, pipe cutter, pipe wrenches, stud finder, high-heat silicone sealant

As we’ve discussed earlier also, indoor tankless hot water heaters are specifically designed for indoor uses.

However, some indoor tankless models use the conversion vent kit so that the heater can be installed outdoor.

Moreover, each and every indoor tankless model should exploit the venting system in order to transfer the by-product of the gas combustion out.

And, at the same time, air for combustion can be either taken from the air present inside the home or from the outside atmosphere.

Again, if you’re planning to install the unit in a confined space such as a closet then, in that case, fresh air needs to be delivered from the rooms in the vicinity with the help of additional inlets on the door.

All I can say is, careful planning will save you both time and money.

Wrapping Up Indoor Tankless Water Heater Review

First and foremost, I would like to thank you for being with us till the end.

Moreover, I would like to bring to your notice that I along with my core team have put loads and loads of effort into coming up with this idiosyncratic superlative comprehensive buying guide.

And, if you liked our effort and want to appreciate us, then please do share this piece of information with the ones who are in need of it.

After all, sharing is caring, isn’t it?

Cutting long-story-short, let’s get back straight to the topic, right?

Trust me, almost all the indoor tankless water heaters that made it to our list are of high quality and worth the investment.

You’ll not regret investing in this little beast, and I can affirm that your investment will definitely, pay you in the longer run.

Moreover, the term “best” is relative and so what may be the best indoor tankless heater for me might not suffice your requirements and vice-versa.

So, always look for an indoor water heater that not only caters to your needs but also falls well within your budget.

Are you interested in knowing which indoor tankless water heater currently I’m using?

Click the link

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