What Size Tankless Water Heater Do I Need For My Family

Beginner Info, Tankless Water Heater

what size tankless water heater do I need
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Well, I was overwhelmed with the fact that a tankless water heater is capable of providing endless hot water if sizing is done correctly.

However, the term if “sizing” is done correctly put my mind into a confused “spot”.

I was literally inquisitive to find the hidden meaning of it.

It wasn’t as easy as it seems to be and you’re definitely gonna realize it at the end of the post ONLY IF you’ve not skipped any portion of the article.

The piece of information that we’ve curated is worth both your time and money because, at the end of the post, I’m also going to share my “top 3” picks for the month.

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

Residential Tankless Water Heater Sizing Guide

Number of Users Electric Tankless (GPM) Capacity RequiredGas Tankless (GPM) Capacity Required
 1 or 2  30  40-50
 2 to 3 50 40-50
 3 to 4 80 50-75
 5 + 80+ 75+

It goes without saying that a tankless hot water heater has gained popularity not only in the USA but across the globe.

And, the credit goes to not only the advanced and innovative technology that these little beasts are equipped with but also the value that it brings to the table in the form of energy efficiency, user convenience, longevity, etc.

In my last article, I’ve explained clearly why a tankless water heater can provide you with an endless supply of hot water.

I left the other part, that is, “correct sizing” of a tankless water heater for the next post.

Trust me, in order to reap maximum benefits out of a tankless water heater, be it an electric tankless, or a gas counterpart, you need to be careful when it comes to choosing the RIGHT size.

I know many of you would be wondering what is the SECRET behind the sizing as I’ve taken the name a couple of times, right?

Sizing is directly related to the flow rate which is measured in gallons per minute.

From the correct sizing of a tankless water heater, what I mean is you need to opt for the flow rate the suffice the flow rate requirement of the fixtures that you want to run simultaneously.

A bit confusing, right?

Don’t worry, keep reading, you’re gonna get every nuts and bolt of what size tankless water heater do I need?

Frankly speaking, neither you want a too small tankless heater nor a bulky and huge one either which has a capacity multifold than your requirement.

To be honest, both the aforementioned tankless models would only bring dissatisfaction and inconvenience to you.

It goes without saying that a tankless hot water heater size should be appropriate to your household hot water requirements so that you can reap the maximum benefits out of it.

In order to figure out what size tankless water heater do you need, you need to do your research around mainly two things.

  • First and foremost, you need to find out the maximum water needs that you would be having at peak hours
  • Secondly, you need to find out how much flow rate, that is, gallons per minute is the tankless model that you’re opting for can heat up, and by how many degrees

As per my experience, knowledge, and research, I can affirm that in order to correctly size the tankless water heater, it is really important that as an end-user, you need to make a rough estimation of maximum hot water needs at any point in time.

In case, you’re completely new to it and doesn’t have any clue, then please allow me to help you with some numbers and facts, if you like then you can use it as a reference point.

Frankly speaking, most of the households have the hot water requirement somewhere between 9 PM to 11 AM.

Correct me, if I’m wrong, but that is the time when most of us expedite the water-related activities for showering, running the washing machine, dishwasher, faucet, etc.

So, in order to calculate the maximum flow rate that you would be requiring at peak hours, I’ve come up with a table which clearly depicts the GPM against some commonly used fixture.

I’m sure that it would be of great help to you when it comes to calculating the flow rate.

Fixture  Gallons Per Minute (GPM)
 Shower 2.0 – 3.0 GPM
 Faucet (kitchen, bathroom) 1.0 – 2.0 GPM
 Dishwasher 1.5 – 2.0 GPM
 Washing Machine 2.0 – 2.5 GPM

For example, if you’re taking a shower (100% flow and 110˚F hot water) and simultaneously use two faucets (100% flow and 110˚F hot water), you will need at least 5 GPM tankless water heater.

The tankless water heaters do come with certain limitations and might not be the preferred choice in case, your flow rate demand exceeds 12 GPM at any point in time.

To be honest, if the maximum flow rate requirement falls in the range of 2 and 12 GPM, then only opt for a tankless hot water heater.

Above or below this range opt for some other better alternatives.

However, the good news is, 5 to 10 GPM are the most appropriate for most households.

Again, if your requirement of flow rate is less than 8 GPM, then my suggestion to you would look for an electric tankless water heater as it would reap maximum benefits.

For 8 GPM and above, a gas tankless water heater will do the trick for you, irrespective of whether you can consider buying propane or a natural gas version.

What size tankless water heater do I need to replace a 50-gallon water heater?

You might be curious about knowing the tankless heater size in case, you want to replace a 50-gallon water heater, right?

Their is a tangible difference right?

With a tank-styled water heater, you’ve got a storage capacity of 50 gallons, right?

But, a tankless water heater heats the incoming groundwater on-demand and doesn’t store even a gallon of hot water.

So, sometimes people get confused about the sizing when they want to upgrade from a tank-style heater to a tankless counterpart.

Let’s understand it with an example.

Suppose you spent about 10 gallons of hot water in a shower that lasted for somewhere around 10 to 15 minutes.

And, you’re running the dishwasher, a couple of faucets, and a washing machine simultaneously, then it is quite obvious that the 50 gallons of hot water would not last long.

However, the best part with a tankless water heater is that it heats the water on demand so storage isn’t an issue.

In simple words, a tankless water heater can supply you with endless hot water if the flow rate demand syncs well with the tankless model flow rate capacity.

So, to replace a 50 gallons tank-based water heater, let’s see what all you need

  • 10 GPM gas tankless water heater or at least a 27 kW electric tankless water heaters such as EcoSmart Eco 27 and this holds true if you’re residing in the northern part of the United States
  • On the other hand, if you’re residing in the southern part of the United States then even a 7 GPM gas tankless heater or its 18 kW counterpart will do the trick for you

Moreover, if you’re planning to buy a gas tankless water heater, then my suggestion would be to opt for the brand Rinnai.

I’ve been personally using it for quite a few years now, and have also been recommending it to my clientele as it is not only worth the investment but also affordable.

The tankless heaters from brand Rinnai are user-friendly, highly energy-efficient, and most importantly delivers performance as per your expectation compromising on lifespan or usability.

What Size Tankless Water Heater Do I Need For A Family Of 5? 

Let’s understand first the magic behind the number 5 and why is it so important.

Suppose you’re a family constituting of 5 members then it is quite obvious that during peak hours a couple of faucets, showers, etc would be running simultaneously.

Furthermore, you might also be using a dishwasher or a washing machine along with other fixtures, right?

So, you need to take the number of family members into account along with the related permutation and communication so that you can do the tankless heater sizing properly with minimum to no loopholes.

So, from my past experience as well as my client references and feedbacks, I can affirm that nothing less than 10 GPM would do the trick.

Yes, you heard it RIGHT- 10 GPM

In case, you’re planning to buy an electric tankless water heater, then opt for ECO 36 or something similar to reap the maximum benefits out of your tankless heater.

Though the minimum requirement for an electric tankless heater for a family of 5 is 27 kW still I recommend 36 kW as it has given better results to my clients.

On the other hand, if you’re a resident of a southern part of the United States wherein the incoming supply water is slightly on the warmer side then anything above 7 GPM gas tankless heater would do the trick for you.

Or, an 18 kW electric tankless water heater similar to ECO 18 would most probably suffice to your hot water requirements.

 You need a powerful tankless water heater for the northern part of America or other similar regions because the tankless heater has to work extra hard to bring the water temperature up to 110˚F or 120˚F. 

Does size of home matters when it comes to buying a tankless hot water heater?

This is yet another interesting question that I’ve been asked frequently by my clientele.

And, I’m assuming that many of the avid readers of this blog would be interested to know a legitimate answer to this query, right?

Well, it’s not the size of your household matters but the number of people residing in a particular household.

On the other hand, larger households might require more than one tankless water heaters such as under-sink or instant-demand water heaters to make things more comfortable and convenient for the resident.

Let’s dig a little bit more.

When it comes to the installation of a tankless water heater, definitely, size of the household matters.

But, you don’t have to worry if enough space isn’t present in your household.

You can easily opt for an outdoor tankless water heater or even the indoor counterparts that are small, compact, sleek designed, and can be installed in tiny and non-conventional spaces.

But, at the same time, you also need to ensure that your tankless beast is capable of handling occasional usages of hot water running individual faucets.

Of course, you need to do the sizing based on the times of the high usages.

In simple words, you might not be using hot water all the time but it has nothing to do with sizing.

Peak hour usages will define the sizing of your tankless hot water.

Let’s understand it this way if you’ve got guests on a frequent basis, or wedding planning or other ceremonies that involve guests visiting your venue on a regular basis, then you’ve no other option but to include it into the peak hour use as well.

Failing to do so will completely mess up with the tankless hot water heater performance, and is definitely, not for a good reason.

Does supply water temperature have an influence over the sizing of a tankless water heater?

Of course, incoming groundwater temperature plays a crucial role in deciding the flow rate of a tankless water heater that you’re planning to buy.

We’ve discussed earlier also, in this post, how a tankless heater bought for a northern part of America would differ from a southern part.

What makes a tankless water heater different from a regular one is that it steams the incoming supply water instantly or you can call it real-time/on-demand “heating” as the water runs into your house through the pipe.

In layman’s terms, it implies that the rate of water flow outputting your tap is determined by the flow supplied by your heater.

The good thing about the mechanism used in a tankless water heater is that it allows you to run multiple fixtures simultaneously without compromising on the speed(flow rate) of your tap.

I’m attaching a self-explanatory video for your perusal.

Let’s assume the temperature of your home’s incoming water supply is 45°F, and your shower (connected to your tankless heater) is expected to deliver water at 105°F; the required temperature rise is 60°F.

Expected Shower Temperature (105°F) – Incoming Water Temperature (45°F) = Required Heater Temperature Rise (60°F)

If your shower flows at a rate of 1.8 GPM, your heater must heat 1.8 gallons of water by 60 degrees Fahrenheit every minute to achieve the desired temperature.

Also, it’s worthy to note that the average ground temperatures may differ for different US states because some states are generally warmer or colder than others.

Some states are estimated to have a temperature as high as 75 degrees, while others can be low as 35 degrees.

Knowing the groundwater temperature of your state helps in calculating how hard your heater will need to work.

Nonetheless, if you’re not sure what to choose from or where to start from then what I would suggest is, start by assuming a temperature of 40 degrees to ensure you don’t underestimate the amount of temperature rise that would be needed.

Tankless Water Heater Size FAQs

Please allow me to answer a couple of questions related to the tankless water heater sizing.

Does the lifespan of a tankless water heater depend on sizing?

As per my knowledge and feedback from my clientele, I can affirm that type plays a crucial role rather than size when it comes to deciding the lifespan of a tankless water heater.

For example, a gas tankless water heater would last longer as compared to its electric counterpart.

In terms of years, a gas tankless heater would last for up to 10 years and an electric tankless will hardly survive a decade until and unless maintained properly.

Where can I find the right model size?

Departmental plumbing store is the right place to find tankless water heaters of different sized models.

In case, you’re the one like me who prefers to shop online, then e-commerce websites do offer tankless heaters, and if you’re lucky enough, then you might end up getting some really great deals.

What size tankless water heater can I install myself?

Well, whether you’re a first-time buyer or a seasoned professional, my humble request to you would be to hire a verified technician for the installation purpose.

Just for your information, some tankless heaters models warranty may become void if they aren’t installed by a professional.

Don’t consider it as yet another DIY activity until and unless you’ve got prior experience in plumbing or a related field.

What size tankless water heater is easier to maintain?

The smaller version is of course easier to maintain and requires less effort.

Similarly, electric tankless is easier to maintain as compared to their gas counterpart.

The quality of the incoming water supply plays a significant role in deciding on the frequency of the maintenance process.

For example, if the water in your area is quite hard and contains a high percentage of minerals then you need to flush your tank at least twice every year.

You can also take the help of vinegar from tackling the deposited sediments inside the unit.

What are the prices for different tankless water heater sizes?

The price of a tankless hot water heater definitely depends upon its size.

The smaller version of both electric and gas tankless heaters are cheaper as compared to the commercial or larger version.

You’ll get a good electric tankless water heater in the range of $150 and $900.

Of course, outliers do exist and I’m not denying about it.

On the other hand, a high-quality gas tankless water heater would cost you somewhere in the range of $1000 and $2000.

Wrapping Up The Tankless Water Heater Sizing

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

Secondly, I would like to bring to your notice that I along with my team have put loads and loads of effort into coming up with this idiosyncratic superlative high-quality informative guide.

And, in case, you found it useful, then feel free to share it with like-minded people.

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

We’ve tried to the best of our capabilities to discuss even the minutes of the parameters that can impact the sizing of a tankless water heater.

Adding quite a few examples was really important from the newbies’ and first-time buyers’ point of view.

Overall, we tried to present the complex information in the best possible way so that non-technical readers can also reap maximum benefit out of the post.

To conclude, do whatever you can do to get the sizing of a tankless water heater right.

Failing to get sizing right can give birth to a series of problems, and in order to get rid of them, you might have to spend a tangible amount of time and money.

And, if you’ve got a scarcity of time, then the best thing that you can do is to take the help of a certified professional or hire a technician so that things fall well in place.

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