# How To Determine Tankless Water Heater Size

## How to Select the Right Size Tankless Water Heater

A 50-gallon electric water heater costs around \$1,000, whereas a natural gas water heater of the same size costs approximately \$1,200. Alternatively, you may send an email to reviews@thisoldhousereviews.com if you have any comments or questions regarding this piece.

### Step 1:

For a 50-gallon water heater, an electric heater costs around \$1,000 and a natural gas heater of the same size costs approximately \$1,200. Send an email to our Reviews Team atreviews@thisoldhousereviews.com if you have any feedback or questions regarding this post.

### Step 2:

Calculate the temperature rise that is necessary. To calculate the temperature rise, subtract the entering water temperature from the desired output temperature and multiply by 100. Assume that the incoming water temperature is 50 degrees Fahrenheit unless you know better. You may rest assured that you will not undersize your tankless unit if you use the low temperature assumption). If you reside in a warm climate, the temperature of your water will most likely be significantly higher. For the majority of applications, water should be heated to around 105–115°.

### Step 3:

Example of sizing: An typical shower will be between 104 and 106 degrees Fahrenheit and utilize 2.6 gallons of water. Assuming that the water temperature entering your home is 40° and that you wish to create enough hot water to run two showers at the same time, what temperature rise would you need to produce to achieve this goal? Answer:You’ll need to boost the temperature of the entering water from 40 degrees to 105 degrees. The ability to heat a minimum of 5.2 gallon of water will be necessary.

## Flow Rates

Is there a limit to how much hot water you may use at once? You need to operate two showers at the same time, or a shower and a pair of sinks, or anything similar. The figure below illustrates the range of water consumption ranges as well as the typical water temperatures for a variety of fixtures. In order to determine your total simultaneous water requirements, we recommend that you use the following reference points: 2.5 gpm for showers and 1.0 gpm for bathrooms.

### Fixture

 Tub 4.0 GPM 102°F Shower 2.5 – 3.0 GPM 104°F Washing Machine 2.0 GPM 120°F Dishwasher 1.5 GPM 110°F Kitchen Sink 1.5 GPM 110°F

Consider the following scenario: If you are taking two showers at the same time, you will require 5 gallons of hot water per minute from your tankless water heater. A shower and the washing machine would each use 4.5 gallons of water per minute from the water heater, thus you would need to turn on both at the same time. In any of these scenarios, you’ll want to make sure that the unit you choose is large enough to accommodate or surpass the amount of hot water you’ll require at the same time.

It is important to note that tankless water heaters are designed to heat only potable (drinking) water, and that the water entering a tankless device should not be pre-heated.

### Other Sizing Notes

Consider the following scenario: If you are taking two showers at the same time, you will require 5 gallons of hot water per minute from your tankless hot water heater. 4.5 gallons per minute would be required from the water heater if a shower and the washing machine were both being used at the same time. Any of these scenarios necessitates the purchase of a hot water heater that is large enough to accommodate or surpass the amount of hot water you require simultaneously. The intake water to a tankless water heater should not be preheated since tankless water heaters are meant to heat only potable (drinking) water.

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## What Size Tankless Water Heater Do I Need? (For Family Of 2,3,4,5,6)

When it comes to tankless water heaters, one of the most common mistakes is purchasing a device that is not powerful enough to meet all of our hot water demands. You don’t want a tankless heater that’s too little, nor do you want one that’s too large and would waste energy unnecessarily heating your home. The size of your tankless water heater should be as close to your household’s hot water requirements as feasible. In what size tankless water heater do I need to invest my money? In order to determine how many GPM tankless water heaters I require for the gas unit and how many kW I require for the electric unit, I must first determine how many GPM tankless water heaters I require for the gas unit.

1. What is the greatest amount of hot water you require? It’s important to know how much water per minute (measured in gallons per minute, or GPM) a particular tankless water heater can heat up, as well as how many degrees it can heat it up by.

In what amount of hot water do you require the most? It’s important to know how much water per minute (measured in gallons per minute, or GPM) a particular tankless water heater can heat up, as well as how many degrees it can heat it up.

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

What is the maximum amount of hot water you require; It’s important to know how much water per minute (measured in gallons per minute or GPM) a particular tankless water heater can heat up, as well as by how many degrees it can do so.

## Difference Between Maximum Water Flow And Realistic Maximum GMPs

When comparing the specifications of different tankless heaters, you will see that they all list the maximum GPMs. When it comes down to it, the highest GMP that your tankless heater will truly reach might be far lower. What is the source of the discrepancy? Because the maximum water flow in GMP is calculated by heating water to 77 degrees Fahrenheit, The inlet temperature of the water that is currently in your pipes is quite important. For example, in south Texas, the inflow water temperature is 77 degrees Fahrenheit.

1. That represents an additional 40 degrees Fahrenheit differential that a tankless water heater must overcome.
2. Because the input temperature is 77 degrees Fahrenheit in Texas, we can really obtain 10 GPM of 110 degrees Fahrenheit water.
3. In Minnesota, on the other hand, the inlet water temperature is 37 degrees Fahrenheit.
4. You don’t come from Minnesota or Texas, do you?
5. An additional example based on the infographics shown above is as follows: If you reside in Florida (inlet temperature of 77 degrees Fahrenheit), the Rinnai RU160iP SE+ Series tankless heater will have a maximum water flow of 7.1 GPM at its maximum temperature.
6. If you reside in New York, on the other hand (with an intake temperature of 52 degrees Fahrenheit), the same tankless water heater may deliver a maximum water flow of 4.5 GMP.
7. In New York, the heater must contend with an additional 25 degrees Fahrenheit.
8. It’s important to consider the operating costs as well, especially with larger units.

You can find out how much power larger electric tankless water heaters consume by visiting this page. Another useful piece of information about propane units is how much propane is consumed by these on-demand hot water heaters.

### What Size Tankless Water Heater Do I Need For A Family Of 2, 3, 4, 5, Or 6?

When it comes to tankless water heater sizing, one of the most often asked topics is how much of a unit you need for a household of multiple people. Obviously, a tankless water heater designed for a family of three will be smaller than one designed for a family of five. But what are the specific GPM (for gas-powered engines) or kW (for electric-powered engines) figures? Because of the changing temperature of the water entering the tankless hot water heater, determining the correct size of the tankless hot water heater is difficult.

Unfortunately, the confidence ranges are extremely wide.

Number Of Family Members: Gas Tankless Heater Size (GPM) Electric Tankless Heater Size (kW)
What size tankless water heater do I need for afamily of 2? 6-8 GPM 10-18 kW
What size tankless water heater do I need for afamily of 3? 7-9 GPM 15-23 kW
What size tankless water heater do I need for afamily of 4? 8-10 GPM 20-28 kW
What size tankless water heater do I need for afamily of 5? 9-11 GPM 25-34 kW
What size tankless water heater do I need for afamily of 6? 11+ GPM 34+ kW

When it comes to tankless water heater sizing, one of the most often asked topics is how much of a unit you need for a family of several people to be comfortable. Naturally, a tankless water heater that is lower in size will be required for a household of three rather than a tankless water heater that is larger. But what are the specific GPM (for gas-powered engines) or kW (for electric-powered engines) figures? Because of the fluctuating temperature of the water entering the tankless hot water heater, it is difficult to determine the precise size of the tankless hot water heater required.

Unfortunately, the gaps between the estimates are rather big (see table below).

### Looking At Specifications Sheets

It is common to find manufacturers specifying a maximum water flow number in GMP or a maximum electric power number in kW on specification documents for their products. The GMP number for gas-powered tankless water heaters is often found on the product label, whereas the kW number for electric tankless water heaters is found on the product label. As we’ve shown, the maximum GMP is a function of context. It is dependent on where you live in the United States (because that affects the inlet water temperature).

• Comparing the maximum wattage of different tankless heaters (as we have done in the table of the best tankless heaters below) allows us to determine how powerful they are in comparison.
• Check here to see if investing in an energy-efficient tankless water heater is truly worth it (we performed some calculations).
• For example, if you want to replace your current 50-gallon water heater, the first question you should ask is what size tankless water heater you need.
• What size tankless water heater would be appropriate for a household of five, for example.

## What Size Tankless Water Heater Do I Need To Replace A 50 Gallon Water Heater? (Example1)

Here’s how things work in this situation: You now have a tank-style water heater that holds 30, 40, 50, or even 80 gallons of water and wish to upgrade to a tankless water heater. The most significant distinction, of course, is that a water tank provides, say, 50 gallons of hot water, but a tankless water heater provides water heating on demand. For example, during a typical 10-minute shower, you use around 10 gallons of hot water on average. Taking 3 showers, running a few of faucets, running a dishwasher, and so on will easily deplete those 50 gallons in no time.

Instead of storing hot water, the tankless heater’s strong heating exchanger warms the water as it is needed, up to a particular maximum GMP limit, depending on the model. In order to replace a 50-gallon water heater, you would require, approximately speaking, the following items:

• If you live in the northern region of the United States, you should have a 10 GPM gas tankless water heater or at least a 27 kW electric tankless water heater. If you live in the southern region of the United States, you should have a 7 GPM gas tankless water heater or at least an 18 kW electric tankless water heater.

As a result, Rinnai, the world’s leading manufacturer of gas tankless heaters, provides a broad range of models ranging from 7 GPM to 11 GPM: Rinnai’s gas tankless versions are available in a variety of sizes. As previously said, they are considered to be the top gas tankless water heater brand. Please keep in mind that this is simply an approximate estimation. The prudent course of action is to get a tankless heater that is somewhat more powerful than the anticipated need. It is preferable to be safe than sorry.

## What Size Tankless Water Heater Do I Need For A Family Of 5? (Example2)

If five individuals reside in the same house, they can use multiple faucets or showers at the same time. This must be taken into consideration while determining the appropriate size of a tankless water heater. Showers are the home hot water user that consumes the most hot water the fastest. 5 persons can also operate many hot water taps at the same time, as well as a dishwasher and do laundry, among other things. In summary, if you live in the northern portion of the United States, where the input water temperature is lower, you would require a 10 GPM gas tankless heater or a 27 kW electric tankless heater.

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For those who reside in the southern part of the country, the tankless water heater’s capacity might be lowered by up to 30 percent.

Keep in mind that, especially with larger units, tankless water heater circulation pumps can save you a significant amount of money on hot water.

You won’t have to wait for hot water to start flowing, squandering all of the cold water that would have been wasted in the meanwhile.

#### How Many Tankless Heaters Do I Need?

This is a rather typical topic, especially when it comes to larger homes. Here’s how it works: In the majority of situations, one tankless heater is sufficient to heat an entire house. For those who live in really large homes (2 or more bathrooms), even the largest Rinnai gas tankless water heater with a flow rate of 11 GPM will not be adequate to meet all of their simultaneous hot water demands. It makes logical in these situations to install two tankless water heaters. The most common combination is as follows: The largest gas unit (11 GPM, 199,000 BTU) and the largest electric unit The large tankless water heater meets the majority of the household’s hot water requirements.

Alternatively, you might utilize two units for different parts of the home, one for one section and another for the other section of the house. Specifically, the plumbing for each units is separate in this instance. I hope this has been of assistance.

## What Size Tankless Water Heater Do I Need?

Note from the editors: We receive a commission from affiliate links on Forbes Advisor. The thoughts and ratings of our editors are not influenced by commissions. Unlike traditional tank water heaters, tankless water heaters give continuous hot water to the kitchen and bathroom. For many homes, installing tankless water heaters represents a welcome break from the deplete-heat-wait cycle associated with traditional tank-style water heater installation. However, reducing the tank also implies that the tolerance margins will be reduced to a bare minimum.

Properly sizing the tankless water heater ensures that you will never be without hot water—and that you will not be forced to purchase a system that is either too large or too expensive.

Testimonials from customers Exceptionally well-written Performance Platinum 9.5 GPM Liquid Propane Water Heater by Rheem Performance Platinum 9.5 GPM Liquid Propane Water Heater by Rheem 3Rinnai RU199iP RU Model Series 3Rinnai RU199iP RU Model Series 3Rinnai RU199iP RU Model Series 3Rinnai RU199iP RU Model Series 3Rinnai RU199iP RU Model Series Testimonials from customers Exceptionally well-written 3Rinnai RU199iP RU Model Series 3Rinnai RU199iP RU Model Series 3Rinnai RU199iP RU Model Series 3Rinnai RU199iP RU Model Series 3Rinnai RU199iP RU Model Series 4Rinnai V53DeP V Model Series 4Rinnai V53DeP V Model Series 4Rinnai V53DeP V Model Series 4Rinnai V53DeP V Model Series Model Series: Rinnai RL75eP RL Model Rinnai RL75eP Testimonials from customers Exceptionally well-written Model Series: Rinnai RL75eP RL Model Rinnai RL75eP (Please keep in mind that all information and pricing are current as of publishing and are subject to change.) If you’re considering purchasing a propane tankless water heater, you may feel overwhelmed by the number of options available.

Price, customer rating, maximum GPM, heating capacity (in BTUs), and Energy Star certification were all taken into consideration while compiling this top-five ranking.

## What a Tankless Water Heater Does

Traditional tank-style water heaters, in contrast to tankless water heaters, heat 40 to 50 gallons of water using a gas or electric burner to heat the water. The burner helps to maintain that temperature by turning on and off intermittently when the water temperature lowers. Maintaining the temperature of a pot of water on the stovetop by turning the burner on and off as needed is analogous to this. Tankless water heaters do not store hot water in a reserve tank like traditional water heaters.

1. They are energy efficient.
2. The majority of homes have one or two tankless water heaters, which are often positioned in the basement, mudroom, utility room, or hallway of the house.
3. Customers with tank-style heaters experience the same transient temperature difference as those who use faucet-style heaters because of the distance between the water heater and the faucet.
4. The installation of supplemental heat recirculators, which circulate the water in a continuous loop between the faucet and the heater, is an option for certain households.

There are similar systems in hotels that are designed to maintain hot water near the faucet and reduce waste water usage. Some tankless water heaters are equipped with built-in heat recirculation systems.

## How to Calculate the Right Size of Tankless Water Heater

Temperature rise is defined as the difference between the groundwater temperature in your location during the winter, or the coldest time of year, and the recommended set temperature of your tankless water heater. To find out what the typical winter groundwater temperature in your location is, look at a map showing average winter groundwater temperatures. Alternatively, during the coldest time of year in your location, you may use a thermometer to monitor the temperature of your water as it is drawn directly from the ground (usually, at an exterior faucet).

### Determine Peak Hot Water Demand

It is the difference between the groundwater temperature in your location during the winter, or when it is the coldest, and the temperature you want your tankless water heater to operate at when it is the desired setting temperature. To determine the temperature of groundwater in your region, see a map showing average winter groundwater temperatures. Another option is to use a thermometer to check the water temperature while it is being drawn from the ground, especially if it is the coldest time of year in your location at the time (usually, at an exterior faucet).

Temperature rise is the difference between the groundwater temperature in your location during the winter, or the coldest time of year, and the recommended set temperature of your tankless water heater.

Alternatively, during the coldest time of year in your location, you may use a thermometer to monitor the temperature of your water as it emerges from the ground (usually, at an exterior faucet).

### Choose a Tankless Water Heater

Tankless water heater manufacturers provide calculation tables or online calculators to assist you in determining the best model for your needs based on peak hot water demand and the temperature rise in your location. For example, if the temperature rise in your location is 60 degrees, your residence may have a peak hot water demand of 6 gpm at its highest point. This may direct you to a few of models that meet the bill in this situation. However, if the temperature rises over 40 degrees Celsius, the manufacturer may propose totally other models.

Alternatively, if the temperature rise remains constant but the rate of consumption fluctuates, you will need to explore alternative tankless heater types. You must compare and contrast the two sets of information in order to determine the most appropriate tankless water heater for your home.

## Tankless Water Heater Pros and Cons

• When compared to huge tank models, little units take up less room. There is no need to wait for the hot water to cycle because there is continuous hot water. Because of the elimination of standby hot water, there will be no unnecessary heating of water.
• There is no hot water stored in reserve in case the electricity goes out
• When all aspects are taken into consideration, it does not cost less than tank models. Excessive scaling as a result of the extremely hot burner, resulting in a larger requirement for routine maintenance

## Compare Quotes From Top-rated Water Heater Installers

Estimates are provided without obligation.

## What Size Tankless Water Heater Do I Need? (+ Sizing Calculator)

A system that is too tiny will not be able to deliver enough hot water to suit the demands of your entire household, so don’t skimp on this purchase.

This is why it is critical to have the right size before making a purchase.

Contents

• In the case of a tankless water heater, the first step is to determine the flow rate. Putting it all together
• Step 2: Temperature increase
• Step 3: Putting it all together Video
• In the case of a tankless water heater, the first step is to calculate the flow rate. Step 2: The temperature begins to rise
• Step 3: Putting it all together
• Step 4: Video

## How to Size a Tankless Water Heater

To put it another way, tankless water heaters, also known as on-demand water heaters, are rated according to their maximum output water flow rate at a given temperature rise. So, in order to properly size a tankless water heater, you must take into account two factors:

1. How many gpm (gallons per minute) of hot water you’ll use during peak consumption periods is calculated. Keep in mind that tankless water heaters do not store water, but rather heat it as it passes through them. The needed temperature rise, which is determined by the parameters for the input water temperature and the output water temperature

What happens if you are undersized? That was a bad idea! Most water heaters will automatically reduce the supply of hot water if the demand for hot water exceeds the maximum capacity, even if it is just for a brief period of time. As a result, there will be less hot water available at each outlet, resulting in a temperature and/or pressure reduction. Furthermore, a tankless water heater that operates at maximum capacity all of the time is more likely to fail prematurely. What happens if you go a little too far?

The main drawback is the excessive up-front expense.

### Step 1: Flow Rate – How Many GPM for a Tankless Water Heater

Begin by calculating your peak hot water use requirements. This may be accomplished by referring to the chart below. It is a list of the typical flow rates of several types of water outlets available for purchase in the United States. On the other hand, you may seek up your individual fixtures and other items on the internet or in their product manuals. Simply decide which devices you want to be able to operate at the same time and how many of them you want to be able to run at the same time.

In the case of two showers and one kitchen faucet operating at the same time, your necessary maximum water flow is as follows: 2.5 gpm plus 2.2 gpm equals 4.7 gpm.

The necessary flow rate for WaterSense-certified goods is 2.0 gpm plus 1.5 gpm, which equals 3.5 gpm. It’s just that simple! But, before you get started, consider the following suggestions:

• By anticipating the highest demand during peak hours, such as the morning, you can assure that you will always have hot water available, no matter what happens. An further benefit is the fact that a tankless water heater that does not have to operate at full capacity all of the time is likely to survive far longer. At the same time, with a little forethought, you will be able to drastically cut peak demand. It entails taking turns in the shower, allowing the dishwasher to do its work while everyone is away from the house, and preparing your meals before or after the showers are completed. You must obviously consider not just the amount of bathrooms in your home, but also the number of people that will be living under one roof while making this decision. Even in a home with five bathrooms, two persons can only use two showers at the same time
• Consider the following questions: Will the water heater service your complete home or only portions of it? It is important to note that the flow rates mentioned below represent total water production, which includes both hot and cold water. As a result, showering with a 2.5-gpm shower head does not guarantee that the water will be hot during the showering session. It is more likely that you will need to mix in some cold to get the required temperature level. As a result, the real demand for hot water is slightly lower
• It is possible to limit flow rates by installing low-flow aerators or fixtures.
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Water Outlet Standard Flow Rate
Hand washing sink 0.5 – 1.5 gpm
Shower head 2.5 (2.0*) gpm
Bathroom faucet 2.2 (1.5*) gpm
Bathtub faucet 3.0 – 4.0 gpm
Kitchen faucet 2.2 gpm
Washing machine 23+ gallons per load, gpm hard to determine
Dishwasher 6 gallons per load, gpm hard to determine

*Products that are WaterSense certified Please keep in mind that older fixtures will most likely have greater flow rates. Please note that we did not include flow rates for washing machines and dishwashers as you can see in the table above. This is due to the fact that we found it quite difficult to obtain credible information on this topic. Some sources state 2 to 3 gpm, while others state 1.5 gpm. Instead, you might run each appliance independently and keep an eye on the timer and your water meter for any anomalies.

As a matter of fact, to get a more scientific perspective on your peak water flow, you may fill a 1-gallon bucket with water and time how long it takes your shower head and other fixtures such as kitchen faucets, bathroom faucets, and other fixtures to fill it up.

Use this formula instead of filling an entire gallon per outlet if you don’t want to squander a full gallon each outlet: Flow rate = 15 / Number of seconds necessary to fill a 14-bucket container

### Step 2: Temperature Rise

The following step is to calculate the temperature rise that is necessary. All you have to do is subtract the temperature of your input water from the temperature of the desired output water in this situation. Output water temperature minus feed water temperature equals required temp raise. What is the best way to determine the temperature of your feed water? There are two alternatives available to you:

1. Measure using a thermometer
2. Use our fantastic groundwater temperature map for the United States

Please keep in mind that these are approximations of typical temperatures. The actual temperature varies depending on the season and weather. As you can see, the location of your home in relation to the average groundwater temperature has a significant impact on the temperature of the water. The temperature will naturally be greater in warmer areas in the south, reaching up to 77 degrees Fahrenheit in southern Florida. On the other hand, groundwater temperatures may drop to as low as 37 degrees Fahrenheit in Alaska, sections of North Dakota, Minnesota, Wisconsin, and other northern states with colder climates.

Assume you reside in Michigan, where the average feed water temperature is 40 degrees Fahrenheit.

105 to 115 degrees Fahrenheit output water temperature is considered ideal for everyday household use, so 110 degrees Fahrenheit minus 40 degrees Fahrenheit equals 70 degrees Fahrenheit.

Showering at 105 degrees Fahrenheit is regarded to be the top end of the temperature range that is most pleasant. You want something about 110 degrees Fahrenheit at your kitchen sink.

### Step 3: Putting It All Together

Okay, you know how much hot water you’ll need during peak hours, as well as the temperature spike that will be necessary. In order to complete this process, you must go out and seek for a tankless water heater that satisfies all of the standards. Almost all manufacturers include sizing charts with their goods, which state maximum flow rates for a specific temperature rise or vice versa, depending on the product. Some manufacturers additionally provide flow rates for various input and output water temperatures.

Keep in mind, though, that manufacturers tend to advertise their products by highlighting the best-case situations, so you should treat the information with caution.

Are you ready to take the next step?

### Video

Do you prefer video? Take a look at this:

## Size Chart

Would you rather watch a film? Examine the following example:

### Example Size Chart

For your convenience, the following is an illustration of a tankless water heater size chart: 6.6 gpm at a temperature rise of 50 degrees Fahrenheit and 4.8 gpm with a temperature rise of 70 degrees Fahrenheit for this specific heater.

### Popular Tankless Water Heaters

Here are some real-world examples of tankless water heaters that are widely used: (Tip for mobile users: Swipe to scroll.)

Model Fuel Type, Power Temp Rise Max GPM of Bathrooms
Rinnai V75iN Natural gas, 180,000 BTU 70 °F 4.3 gpm 1 – 2 bathrooms
50 °F 6.0 gpm 2 – 3 bathrooms
Rinnai RU199iP Propane, 199,000 BTU 70 °F 5.5 gpm 2 bathrooms
50 °F 7.6 gpm 3 bathrooms
Stiebel Eltron Tempra 36 Plus Electric, 36 kW 70 °F 3.5 gpm 1 bathroom
50 °F 4.75 gpm 1 – 2 bathrooms
Rheem RTEX-18 Electric, 18 kW 65 °F 2.0 gpm 1 bathroom
55 °F 2.0 gpm 1 bathroom
EcoSmart ECO 11 Electric, 11 kW 68 °F 1.1 gpm 1 bathroom
48 °F 1.56 gpm 1 bathroom

## Frequently Asked Questions (FAQ)

Which size tankless water heater do I need to provide hot water for a family of five? It’s virtually hard to determine from the information provided. It is dependent on the number of bathrooms and water-using appliances you have, as well as the temperature rise necessary. Follow the steps 1 through 3 in our sizing guide, or use our tankless water heater sizing calculator, and you will receive a satisfactory solution to your concern – guaranteed. I need to replace my 50-gallon water heater, but what size tankless water heater do I need to do so?

• It is dependent on the number of bathrooms and water-using appliances you have, as well as the temperature rise necessary.
• 3.
• The number of tankless water heaters you require is determined by your peak hot water consumption and the temperature rise that is necessary (check sizing guide above).
• Electric tankless water heaters are ideal for households with fewer people or for tiny flats.
• Furthermore, even though it is more expensive up front, putting two smaller units in series can often be more cost effective than installing a single large unit at a single location.
• Thank you for your time!
• She is the head of content production and has completely immersed herself in the home water treatment sector, resulting in her becoming an expert in the field herself.

Gene enjoys reading books on philosophy and social topics, producing music, and going on hikes when he is not at BOS. Find out more about.

## What Size Tankless Water Heater Should You Buy: Sizing For Your Family Needs

Tankless water heaters are the way of the future when it comes to hot water usage in residential and commercial buildings. Tankless water heaters are characterized by their small form and ability to provide hot water on demand. On the other hand, on-demand does not always imply continuous service. Flow rate is the amount of water that may be produced in one minute by a tankless water heater (both electric and natural gas). If the demand for hot water in your household exceeds the capacity of your water heater, you may experience a lack of hot water.

1. Gallons per minute (GPM) is the unit of measurement for tankless water heaters (GPM).
2. During peak hours, the average family consumes around 6.5 GPM.
3. A tankless water heater with a capacity of 4 GPM can deliver enough water for one shower and one appliance to run at the same time.
4. When a tankless water heater is undersized, it will not be able to provide enough hot water to fulfill the needs of your household.
5. A tankless water heater with a flow rate of 4GPM will be unable to heat enough water to fulfill this demand for hot water.
6. A lar ge tankless water heater has greater installation and operating expenses than a traditional tank water heater.
7. For example, a 4 GPM tankless water heater will cost between \$400 and \$700 plus installation, and an 8+ GPM tankless water heater would cost between \$900 and \$2000 plus installation.
8. Hot water on demand is defined as having continuous hot water output for the duration of time that the hot water tap is open.
9. If you have too many hot water faucets open at the same time, the water will become lukewarm if the tankless water heater’s output capacity is surpassed.
10. Installation costs are in addition to the cost of the tankless water heater.

We’ve put together this complete shopping guide to assist you in making the best decision for your family when it comes to tankless water heaters. The following section will lead you through the many various considerations you should make while shopping for tankless water heaters.

## Gallons of Hot Water You Need for a Tankless Water Heater

In both residential and commercial premises, tankless water heaters are the way of the future when it comes to hot water usage. Unlike traditional tank water heaters, tankless water heaters provide hot water on demand. It is important to note that “on demand” does not always imply “continuous.” Flow rate is the amount of water that may be produced in one minute by a tankless water heater (both electric and gas). This might happen if the demand for hot water in your household exceeds the capacity of your water heater’s output.

• Gallons per minute (GPM) is the unit of measurement for tankless water heater flow rates (GPM).
• During peak hours, the average family uses around 6.5 GPM.
• It is possible to run one shower and one appliance at the same time with a tankless water heater producing 4 GPM.
• It is impossible for a tankless water heater to provide enough hot water to suit the needs of a large family if it is undersize.
• It is impossible to supply this hot water demand with a tankless water heater operating at 4GPM.
• There are greater costs associated with installing and operating a lar ge tankless water heater.
• For example, a 4 GPM tankless water heater costs between \$400 and \$700 plus installation, but an 8+ GPM tankless water heater costs between \$900 and \$2000 with installation.
• Opening many hot water faucets at the same time, on the other hand, will diminish the amount of hot water available.
• A whole-house tankless water heater costs on average \$2,810, with installation fees ranging from \$45 to \$200 per hour, with a total installation time of 2 to 8 hours, according to Fixr.com.
• We’ve put together this detailed shopping guide to assist you in selecting the best tankless water heater for your household.

### Tankless Water Heaters GPM Flow Rate Explained

It is the time of day when you use the most hot water at one time that is referred to as peak demand. Tankless water heater size is determined by the flow rate, which is measured in gallons per minute (GPM). The majority of tankless water heaters are capable of producing between 2 and 10 gallons of water per minute on average. During peak demand periods, it will be necessary to total up all of the flow rates of the fixtures and appliances in your home that may be using hot water at the same time in order to establish your water flow rate need during those times.

The only way to determine your specific water flow rate need is to consult the literature that came with your hot water equipment. However, the following list of normal flow rates for popular fixtures and appliancesshould assist you in making an estimate:

Fixture or Appliance Usage: AverageGallons per Minute(GPM) Used
Bathtub 4 GPM
Rainhead shower head Up to 5 GPM
Standard shower head 2.5 GPM
Standard dishwasher 2.5 GPM
High-efficiency dishwasher 0.5 – 1.5 GPM
Standard clothes washer 2.5 GPM
High-efficiency clothes washer 1.0 GPM
Sink faucet 1.5 GPM

Using the expected GPM production as a guideline. There are some fixtures and appliances that have a larger output than others. Using a normal shower head (2.5 GPM) consumes approximately half the amount of hot water as using a rainhead shower head, as seen in the following table (5.0 GPM). The kitchen faucet consumes approximately the same quantity of hot water as other sink faucets, regardless of where they are installed. It is uncommon for many sink faucets to function in tandem for extended periods of time.

### What is a Tankless Water Heater’s Temperature Rise

Once you’ve determined the amount of water flow your tankless unit will require during peak demand periods, you’ll need to figure out how much “temperature increase” it will require. The temperature rise refers to the amount of degrees your hot water heater will need to raise the incoming average groundwater temperature in order to supply enough hot water for your household. For example, suppose the temperature of the entering cold water is 52 degrees Fahrenheit. If you want hot water that is 110°F, you’ll need a temperature raise of 58°F.

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### Putting Flow Rate and Temperature Rise Together

The flow rate and temperature rise of a water heater are both measured in the ratings. If you want to appropriately size your water heater, you must take into consideration both the flow rate necessary and the rise in temperature required.

Ground Water Temperature Expected Gallons per Minute Output
37 F 3.9 GPM
42 F 4.7 GPM
47 F 5.5 GPM
52 F 6.3 GPM
57 F 7.1 GPM
62 F 7.8 GPM
67 F 8.6 GPM
72 F 9.4 GPM

Another example is based on a tankless water heater with a 9.5 GPM output and a temperature rise of 35 degrees. Consider the following scenario: you have four gadgets that may all demand hot water at the same time:

• 1 GPM / 110° for the hot water faucet
• 1 GPM / 110° for the dishwasher
• 2 GPM / 120° for the washing machine.

Furthermore, let’s say that the entering cold water temperature is 50°F. A tankless water heater with a flow rate of 5.0 GPM and a temperature increase of 70° would be required to run all of these devices at the same time. The total flow rate of 5.0 GPM is equal to the sum of all device flow rates combined. The temperature increase of 70 degrees Celsius is obtained by subtracting the entering water temperature (50 degrees Celsius) from the highest device water temperature (120 degrees Celsius).

If you don’t intend to use all of your hot water equipment at the same time, you may save money by purchasing a less costly heater with a lower flow rate instead of an expensive one.

## Are Tankless Water Heaters Worth the Cost

Furthermore, let’s say that your incoming cold water temperature is 50° F. If you want to run all of these devices at the same time, you will need a tankless water heater with a flow rate of 5.0 GPM and a temperature increase of 70° F. The total sum of all device flow rates equals the 5.0 GPM flow rate. By deducting the entering water temperature (50°) from the maximal device water temperature (120°), a temperature increase of 70 degrees is achieved. Having said that, just because the aggregate flow rate of your devices totals 5.0 GPM does not always imply that you require a water heater with a flow rate of 5.0 GPM.

It is possible to save money by purchasing a less costly heater with a lower flow rate if you do not intend to use all of your hot water equipment at the same time.

• Furthermore, let’s say that your incoming cold water temperature is 50°F. In order to run all of these devices at the same time, you would need a tankless water heater with a flow rate of 5.0 GPM and a temperature increase of 70°. The total flow rate of 5.0 GPM is equal to the sum of all device flow rates. The temperature increase of 70 degrees Celsius is obtained by subtracting the entering water temperature (50 degrees Celsius) from the maximal device water temperature (120 degrees Celsius). Now, just because the aggregate flow rate of your devices adds up to 5.0 GPM does not imply that you require a water heater with a flow rate of 5.0 GPM. If you do not intend to use all of your hot water equipment at the same time, you may save money by purchasing a less costly heater with a lower flow rate.

## Electric vs. Gas Tankless Water Heaters

Let’s also assume that your incoming cold water temperature is 50°. To run all of these devices at the same time, you’d need a tankless water heater with a flow rate of 5.0 GPM and a temperature increase of 70°. The total flow rate of 5.0 GPM is the sum of all device flow rates. The temperature rise of 70° is obtained by subtracting the entering water temperature (50°) from the highest device water temperature (120°). Now, just because the combined flow rate of your devices totals 5.0 GPM does not imply that you require a water heater with a flow rate of 5.0 GPM.

### Electric Tankless Water Heaters Cost Less to Buy and Install

Furthermore, let’s say that the entering cold water temperature is 50°F. A tankless water heater with a flow rate of 5.0 GPM and a temperature increase of 70° would be required to run all of these devices at the same time. The total flow rate of 5.0 GPM is equal to the sum of all device flow rates combined. The temperature increase of 70 degrees Celsius is obtained by subtracting the entering water temperature (50 degrees Celsius) from the highest device water temperature (120 degrees Celsius).

If you don’t intend to use all of your hot water equipment at the same time, you may save money by purchasing a less costly heater with a lower flow rate instead of an expensive one.

### Electric Tankless Water Heaters are Easier to Maintain

Because electric units are simpler devices than gas-powered units, they are less expensive than gas-powered units. Because there are fewer components within, there are fewer moving parts that might break down and necessitate a costly repair job. The cost of fixing a propane-powered device is often cheaper than it would be if the equipment were fueled by gas. The majority of tankless water heaters will beep to alert you when tankless water heater maintenance is required.

### Electric Tankless Water Heaters are More Energy-Efficient

The most efficient gas-powered tankless heaters have an energy efficiency of around 85%. When compared to most electric vehicles, which have an average energy efficiency of 98 percent, an 85 percent efficiency rating is considered inadequate. So even though natural gas is less expensive than electricity in your location, choosing an electric unit may result in you saving money on energy expenditures in the long run. Electric heaters are more ecologically friendly than other types of heaters. The production of electricity is already less detrimental to the environment than the combustion of natural gas, and the greater energy efficiency of electric vehicles further adds to the disparity between the two modes of transportation.

### Electric Tankless Water Heaters Can Require Significant Electrical Upgrades

The most important drawback of electric tankless water heaters is the difficulty in installing them on the premises. A separate 240v breaker is required for each burner on an electric tankless water heater. For large GPM models to work properly, three or four 220v breakers must be installed, which means you may need to install an electrical subpanel or make other electrical changes. If you choose an electric tankless water heater with a high output, you may need to build a new subpanel to supply electricity to the water heater.

You’ll need eight breaker slots to accommodate four 240v breakers.

You will thus require the installation of a new subpanel if your present electrical panel does not have sufficient vacant spaces. According to industry standards, one heating element is required for every 2GPM of water production in an electric tankless unit.

### Gas Tankless Water Heaters Produce More Hot Water

A variety of natural gas and propane types are available for tankless gas water heaters. Some purchasers choose a tankless gas water heater over an electric water heater because gas versions can handle higher flow rates than electric water heaters. The best electric units have a maximum flow rate of 8GPM, but some gas ones have a flow rate that is substantially greater. In the case of a big home or an industrial application, you may be forced to choose a tankless heater that is fueled by natural gas.

The majority of on-demand tankless water heaters are capable of operating at a variety of intake temperatures.

In an electric model, the same rise in temperature of 70 degrees Fahrenheit (70 degrees Fahrenheit) will result in around 2 gallons of hot water per minute in hot water, which is a considerable drop in production.

### Natural Gas is Cheaper than Electricity in Some Areas

Given the price disparity between natural gas and electricity, depending on where you reside, a gas-powered device may be more appealing than an electric model. However, even if natural gas is much less expensive than electricity, the gain in efficiency associated with electric models, as well as the anticipated increase in natural gas pricing, may still make turning electric the most cost-effective alternative.

### Indoor or Outdoor Installation Options

Given the price disparity between natural gas and electricity, depending on where you reside, a gas-powered model can be more appealing than an electric one. While natural gas is much less expensive than electricity, the increased efficiency of electric models, together with the anticipated increase in natural gas costs, may still make turning electric the most cost-effective choice.

## Conclusion

According to your location, the price difference between natural gas and electricity may make it more appealing to choose a gas-powered model. Even though natural gas is much less expensive than electricity, the gain in efficiency associated with electric models, as well as the anticipated increase in natural gas pricing, may still make turning electric the most cost-effective choice.

## How To Size A Tankless Water Heater

In the market for a new water heater, you may want to investigate tankless hot water heaters as an option to examine. This type of hot water heater may provide you with a number of various advantages. In addition, you will need to understand how to properly size a tankless water heater.

## What Is A Tankless Hot Water Heater?

It is a type of water heater that does not contain a storage tank, as opposed to standard water heaters. As soon as you turn on your faucet, cold water is instantly turned to hot water, and vice versa.

You will save money on your utility costs because, unlike standard water heaters, you will not be required to heat the water on a continuous basis. Tankless water heaters are also more space-efficient than typical water heaters, taking up significantly less space.

### Sizing Your Water Heater

You will need to determine the appropriate size of your water heater. If you choose the incorrect size, it may not be able to adequately heat the water in your house. Particularly problematic is the situation in which you are attempting to utilize various restrooms or appliances at the same time. You may determine How To Size A Tankless Water Heater by following the procedures outlined below: Step 1: Take some time to sit down and figure out how many devices you’ll need to have hot water for, as well as their flow rates.

• If you want to run your shower and faucet at the same time, you’ll need to figure out how much water each of them can handle.
• The flow rate of the shower head will be 2.6 gallons per minute.
• Low-flow water faucets and shower heads are available for purchase and installation if you wish to reduce your flow rates.
• You will need to subtract the temperature of the incoming water from the temperature of the output water.
• This will assist to guarantee that you do not choose a tankless hot water heater that is too small.
• You will want to choose a temperature range of 105 to 115 degrees.

### Sizing Example

You will need to have a shower temperature of between 104 and 106 degrees to get the most out of it. When you take a shower, it will use 2.6 gallons of water every minute. A minimum of a 60-degree increase in temperature is required, and your tankless hot water heater should be capable of producing 5.2 gallons per minute in order to guarantee that you have the appropriate water temperature. You will need to pay close attention to this since sizing your system incorrectly can result in you not having enough hot water to complete the tasks that you need to do.

Suppose you want to take two showers at the same time, or you want to run many sinks at the same time.

The water from your tankless water heater will be insufficient if you are running two different showers at the same time.

You’ll want to be certain that the heater you choose is the appropriate size.

If you want a higher temperature rise per GPM of water, you may want to look into buying a gas tankless hot water system here.

In order to have a better understanding of How To Size A Tankless Water Heater, contact the Original Plumber right now.

They may sit down with you and go through your use rates to evaluate if it would be more cost effective for you to purchase an electric tankless hot water heater or a gas tankless hot water heater.

Hiring a professional plumbing firm eliminates the need to worry about the installation of the hot water heater or ensuring that you have the proper size. The installation of a water heater may be complex and risky, therefore it is always a good idea to leave it to the experts.