How To Get The Right Size Tankless Water Heater?

How to Select the Right Size Tankless Water Heater

• Tankless water heaters are classified according to the highest temperature rise that may be achieved at a given flow rate.
• For this reason, in order to calculate the appropriate size of a demand water heater for your home, you must first estimate the flow rate and temperature increase that will be required for its application (either the entire house or a distant use, such as a bathroom).
• It is vital to note that you should never attempt to save money by purchasing a tankless water heater that is undersized.

Step 1:

• Make a decision on the maximum number of devices that you wish to run and the overall flow rate of those devices.
• Then total their flow rates together (gallons per minute).
• This is the intended flow rate that you’ll need for the demand water heater that you’ve purchased.
• Consider the following scenario: you anticipate to be able to operate a hot water faucet with a flow rate of 0.75 gallons per minute while also running a shower head with a flow rate of 2.6 gallons per minute concurrently.
• It would be necessary for the flow rate via the demand water heater to be at least 3.26 gallons per minute.
• Installing low-flow water fixtures can help to lower flow rates.

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°.

A demand water heater that delivers a temperature increase of 55° would be required in this scenario.

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.
• As a result, you’ll need a tankless water heater that can provide at least a 60-degree increase in temperature while also dispensing 5.2 gallons per minute of water.

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

Average Flow GPM

Average Temp.

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 only designed to heat potable (drinking) water, and that the water entering a tankless device should not be pre-heated before use.

Other Sizing Notes

• Gas tankless water heaters have the ability to create a greater temperature rise per gallon of water than electric tankless water heaters.
• The majority of demand water heaters are rated for a wide range of water temperature inputs.
• An average flow rate of 5 gallons per minute via gas-fired demand water heaters and a flow rate of 2 gallons per minute through electric demand water heaters will result in a 70°F increase in water temperature in most cases.
• Increased flow rates or decreased intake temperatures can occasionally result in a reduction in the temperature of the water at the furthest faucet.

Recommended Reading:

• Learn how to use a washer dryer combo
• learn about three common misconceptions about washer dryer combos
• learn all you need to know about wall heaters in this comprehensive guide
• and more.
• Infrared Heaters 101: Your Complete Guide to Understanding Them

About Our Team

• Jeff Flowers is just a person who is plagued by a chronic case of curiosity and who frustrates everyone around him with his rambling nonsense.
• In his journey from beer to house living, Jeff is simply attempting to hack his way through life while also writing a few notes about his experiences along the way.
• Alternatively, you can listen to him rant about Austin traffic on Twitter at @Bukowsky, where you can follow his musings as well.

Sizing a New Water Heater

• A correctly sized water heater will satisfy the hot water requirements of your family while also functioning more effectively. As a result, when choosing a water heater, be certain that it is the appropriate size. These are the guidelines for sizing these systems, which you can find here: Water heaters that are tankless or on demand
• System for heating water with solar energy
• Warm-water storage and heat pump (with tank) water heaters.

Consult a trained contractor for assistance in sizing combined water and space heating systems – which may include certain heat pump systems as well as tankless coil and indirect water heaters. If you haven’t already decided on the sort of water heater that would be most appropriate for your house, read on to learn more about choosing a new water heater.

Sizing Tankless or Demand-Type Water Heaters

• When rating tankless or demand-type water heaters, the greatest temperature rise that may be achieved at a given flow rate is taken into consideration.
• For this reason, in order to calculate the appropriate size of a demand water heater for your home, you must first estimate the flow rate and temperature increase that will be required for its application (either the entire house or a distant use, such as a bathroom).
• To begin, make a note of the number of hot water gadgets you anticipate using at any given moment.
• Then total their flow rates together (gallons per minute).
• This is the intended flow rate that you’ll need for the demand water heater that you’ve purchased.
• Consider the following scenario: you anticipate to operate a hot water faucet with a flow rate of 0.75 gallons (2.84 liters) per minute while also running a shower head with a flow rate of 2.5 gallons (9.46 liters) per minute concurrently.

You may estimate the flow rate by holding a pan or bucket under the faucet or shower head for a minute and measuring the flow rate that way.Calculate the gallons per minute by measuring the amount of water and multiplying it by 60.(or liters per minute).The demand water heater should have a flow rate of at least 3.25 gallons (12.3 liters) per minute to meet the requirements.

Installing low-flow water fixtures can help to lower flow rates.To calculate the temperature rise, subtract the entering water temperature from the desired output temperature and multiply by 100.Assume that the entering water temperature is 50 degrees Fahrenheit (10 degrees Celsius) unless you know differently.Holding a thermometer under a cold-water faucet can provide provide an indication of the current temperature.Water should be heated to 120 degrees Fahrenheit (49 degrees Celsius) for the majority of applications.

1. In this case, you’d require a demand water heater that delivers a temperature increase of 70oF (39oC) or higher for the majority of your applications.
2. For dishwashers without internal heaters and other similar uses, you may wish to heat your water to 140 degrees Fahrenheit (60 degrees Celsius).
3. In that situation, a temperature rise of 90oF (50oC) will be required.

1. When the water temperature reaches 140 degrees Fahrenheit, use caution since it raises the risk of scorching.
2. The majority of demand water heaters are rated for a wide range of water temperature inputs.
3. At a flow rate of 5 gallons per minute through gas-fired demand water heaters and 2 gallons per minute through electric demand water heaters, a temperature rise of 70 degrees Fahrenheit (39 degrees Celsius) is often achieved.
4. Increased flow rates or decreased intake temperatures can occasionally result in a reduction in the temperature of the water at the furthest faucet.

Some tankless water heaters are thermostatically regulated, which means that they may adjust their output temperature based on the amount of water flowing through them and the temperature of the water entering them.

Sizing a Solar Water Heating System

Calculating the total collector area and storage volume required to supply 90 percent to 100 percent of your household’s hot water demands throughout the summer is the most fundamental step in designing a solar water heating system. Solar system contractors utilize spreadsheets and computer programs to assist them assess the size of their systems and the number of collectors they need.

Collector Area

• Contractors often adhere to a guideline of around 20 square feet (2 square meters) of collector space for each of the first two family members, with the third family member receiving an additional 20 square feet (2 square meters).
• If you reside in the Sun Belt region of the United States, you should add 8 square feet (0.7 square meters) to your living space for every extra person; if you live in the northern United States, you should add 12–14 square feet.

Storage Volume

• A modest storage tank (50- to 60-gallon capacity) is normally suitable for one to two individuals, although a larger tank may be required.
• It is sufficient for three to four persons to use an 80-gallon storage tank of medium size.
• A big tank can accommodate four to six people comfortably.
• Active systems have a solar storage tank that grows in size in proportion to the size of the collector – generally 1.5 gallons per square foot of collector for active systems.
• When the demand for hot water is minimal, this helps to keep the system from overheating and breaking down.
• In extremely hot and sunny areas, some experts recommend increasing the storage-to-collector area ratio to as much as 2 gallons of storage for every square foot of collector surface.

Other Calculations

Another set of calculations required in estimating your solar water heating system is analyzing the solar resource available on your construction site, as well as establishing the optimal orientation and tilt of the solar collector. More information on these calculations may be found on the solar water heaters website.

Sizing Storage and Heat Pump (with Tank) Water Heaters

• You should utilize the water heater’s first hour rating to determine the appropriate size for your home’s storage water heater, which may include a tankless heat pump water heater. The first hour rating indicates the amount of gallons of hot water that the heater can provide per hour of operation (starting with a tank full of hot water). The tank capacity, heat source (burner or element), and size of the burner or element are all factors to consider. The first hour rating is listed in the upper left corner of the EnergyGuide label as ″Capacity (first hour rating)″ on the label. The Federal Trade Commission requires that all new conventional storage water heaters have the EnergyGuide label, but does not require that heat pump water heaters bear the label. The first hour rating may also be found in product literature provided by the manufacturer. Look for water heater types that have a first-hour rating that at the very least matches your peak-hour demand requirements (the highest energy use during a single 1-hour period for your home). To estimate your peak hour demand, do the following: Determine what time of day (morning, noon, or evening) you use the most hot water in your house and record that information. It’s important to consider the amount of people that will be living in your house.
• Making an estimate of your maximum hot water use during this one-hour time of the day—also known as your peak hour demand—can be done using the worksheet below. Please keep in mind that the spreadsheet does not estimate total daily hot water use.

The worksheet example displays a total demand of 66 gallons during peak hour usage. As a result, this home would require a water heater with a first-hour capacity of 66 gallons or greater.

Worksheet for Estimating Peak Hour Demand/First Hour Rating *

Use	Average gallons of hot water per usage		Times used during 1 hour		Gallons used in 1 hour
Shower	20	×		=
Shaving (.05 gallon per minute)	2	×		=
Hand dishwashing or food prep (2 gallons per minute)	3	×		=
Automatic dishwasher	7	×		=
Clothes washer		×		=
– Top-loader	25
– H-Axis	15
			Total Peak Hour Demand	=

EXAMPLE

3 showers	20	×	3	=	60
1 shave	2	×	1	=	2
1 hand dishwashing	3	×	1	=	3
Peak Hour Demand				=	66

*Estimates are based on averages derived from a variety of publicly available information published on the internet. Various calculators are available on some water heater manufacturer websites, which are depending on the duration of the use case and other criteria.

How to Select the Right Size Tankless Water Heater – Northwind HVAC

• If you’re a homeowner, there’s a good chance you’ve wondered what size tankless water heater you’ll need at some time.
• When picking a tankless water heater, make sure to choose one with the appropriate capacity for your needs.
• As the sole device responsible for delivering hot water to every faucet and shower in your house, choosing the proper size capacity is crucial.
• Beyond capacity, it is vital to consider other factors such as energy consumption, maintenance needs and expenses (including labor), installation, unit lifespan (including the possibility of government incentives), and manufacturer warranties.
• It is the combination of all of these factors, as well as appropriate size, that will determine whether or not a system is appropriate for your home.
• Tankless water heaters are significantly smaller than traditional units, and they are rated according to the highest temperatures that can be reached at different flow rates.

You’ll need to figure out how many devices the water will pass through, how fast the water will flow through each device, and how much temperature rise you’ll need to make your home comfortable.Important: Do not focus on saving money by purchasing a tankless water heater that is too small; doing so will almost surely result in future irritation and problems.First and foremost, here is an easy-to-consume table that summarizes the basic tankless water heater sizing requirements, which are determined by family size and water usage: With that in mind, let’s get started with the facts you’ll need to make an informed decision on which system to install in your house!

Determine the Maximum Number of Devices You Want to Run

• To begin the tankless water heater sizing procedure, you’ll need to figure out how many different devices the unit will be responsible for heating and cooling.
• Showers and faucets around the home, among other things, will be included in this category of objects.
• Once you’ve accounted for all of the devices, you’ll need to figure out their flow rates — for example, 2.8 liters per minute per faucet and 9.8 liters per minute per shower – and add them all together to get the total.
• Having decided the capacity, you will be able to calculate the hot water tank dimensions that will be necessary.
• If possible, water heater capacities should be chosen to fulfill all device needs, with extra capacity being more than welcome in the event that future renovations result in the addition of more water heaters.

Determine Required Temperature Rise

• It is necessary to subtract the incoming water temperature from the intended output temperature of the devices in your house in order to calculate the required temperature rise.
• It is reasonable to presume that your incoming water temperature is roughly 10 degrees Celsius unless you have received particular information from a qualified source.
• Additionally, it’s preferable to approximate the incoming water temperature by choosing a little lower value to ensure that you don’t mistakenly undersize your unit by a small amount.
• The entering water temperature has now been established, and the rest of the computation may be completed at this point.
• It is likely that the majority of households would want their water heated to a maximum of 40-45 degrees Celsius, which means that a tankless water heater with a temperature increase capability of 35 degrees Celsius or above is necessary.

Flow Rates

• The flow rate of a tankless water heater is the next aspect to consider when making a decision.
• Simply said, this is the amount of water you’ll require at any one moment, ensuring that you get a system that is large enough to accommodate your household’s needs.
• Will you be taking two showers at the same time?
• Do you frequently find yourself with numerous faucets running at the same time?
• The following table lists common household fittings, as well as the typical flow rate and temperature requirements for each: You may use this information to calculate the overall quantity of flow necessary.
• Tankless water heaters can provide around 20 liters of hot water per minute, which is plenty if you frequently take two showers at the same time or want to be certain that your water heater has the capacity to do so.

Always ensure that your tankless water heater is sized appropriately for the number of fixtures in your home to ensure that hot water is continuously cycled to all of them, regardless of the mix of fixtures.South Carolina-based North Wind Heating and Air Conditioning will help you install a new tankless hot water heater in your house.Our skilled staff has years of combined expertise in tankless water heater installation and maintenance, and they are well-equipped to handle any problem that may arise.To learn more about our services or to receive a free project estimate, please get in touch with us right now!

How to Size a Tankless Water Heater?

• The power of a tankless boiler – the size of a water heater – is an essential element to consider.
• According to many experts, this indication is critical in determining whether or not the selected model will be able to offer you with the appropriate amount of hot water.
• The selection of the ideal water heater size is critical since both too small and too big water heater sizes have the potential to cause problems.
• Why?
• This is because if the power is insufficient, when you turn on, for example, two faucets and a shower at the same time, the heating device will not be able to maintain the required temperature, and someone will be sprayed with ice water, and you will be dissatisfied with the force with which the water is flowing.
• If you get a tankless water heater that is too large, it will consume more energy or gas, which will result in a considerable rise in your electric and natural gas costs.

The gadget will be ineffective since its power output will be substantially greater than your requirement for hot water.So, how do you go about determining the optimal size for a heater that does not have a tank?There are a lot of practical and straightforward suggestions for people who are interested in learning more.Finding a contractor, on the other hand, is always the best solution.

How to Choose a Suitable Tankless Water Heater Size?

• In order to deal with this topic completely and extensively, you need be familiar with the following fundamental concepts: The amount of water that flows through various devices (for example, a faucet in the bathroom, shower, washing machine, etc.). Gallons per minute (GPM) is the unit of measurement.
• The overall flow rate of water during peak hours of consumption of hot fluids
• the temperature of groundwater in the region in which you live
• and other factors.

• Following the above guidelines, you can simply analyze your hot water requirements and select the appropriate hot water heater size. If you place a high value on your resources and do not have the time to deal with difficulties of this nature, hiring a contractor will help you get out of this scenario in a dignified and professional manner. For this reason, in order to estimate the water flow rate for various devices, you should consult a particular table that contains all of the relevant information. Here are only a few examples: Shower flow rates range from 1.5 GPM for low flow to 3.0 GPM for standard flow
• kitchen faucet flow rates range from 2 to 3 GPM
• bathroom sink flow rates range from 0.5 to 1 GPM
• dishwasher flow rates range from 1.5 to 3 GPM
• washing machine flow rates range from 2 to 3 GPM
• bathtub flow rates range from 4 to 6 GPM.

• Knowing the approximate water flow rate of one or more devices, you may go on to the next phase of the procedure.
• As a result, you must establish what time of day, and more specifically, what hour, is the busiest in terms of the use of hot liquid.
• To be more specific, one needs determine which devices are turned on and how many of them are operating at the same time.
• Furthermore, after adding all of these figures together and consulting the table, you will be able to determine your average GPM.
• On the appliance, the standard water heater capacity is shown.
• In the technical specifications of each tankless boiler, this indication must be provided; by consulting the manufacturer’s website, you may determine the suitable size of the water heater.

Groundwater Temperature

• However, it is not all.
• The temperature of the groundwater in your location is the final, but not the least, significant factor to consider when choosing the appropriate size of a boiler without a storage tank.
• In most cases, 110 degrees Fahrenheit is the average temperature of the liquid to which the water in the house is heated, according to widely acknowledged standards.
• What is the purpose of this?
• In addition, if, for example, the temperature of the groundwater in your location is 52 degrees, your device will need to heat the water to 58 degrees in order to provide water at an appropriate temperature to your customers in your area.
• The water flow rate is affected by this because, as the water cools down, it warms up more slowly, using greater amounts of energy (gas or light) to accomplish the operation and, as a result, reducing the total GPM.

All of this needs to be taken into consideration.Finding a contractor is an option for individuals who do not want to deal with tables and maps of groundwater temperature because they do not have the time.If you still want to deal with this situation on your own, you should be aware that the Internet is a treasure trove of materials that may assist you in your endeavor.One of them is the GPM calculators available online, which may also be used to calculate the temperature of the water at the output.

All that is required is that you enter the appropriate values in the appropriate areas to obtain the desired outcome.Then, determine the size of the water heater that you require.Finding a contractor will substantially simplify your life and prevent the need for you to participate in any additional manipulations with a tankless boiler, which will save you time and money.After all, it will not operate until it has been properly installed and connected by someone.Keep that in mind and select the most appropriate solution for yourself.

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

• An expensive tankless water heater that is not powerful enough to meet our demands is one of the most common blunders people make when purchasing a tankless water heater.
• Tankless heaters should not be purchased based on their size.
• Neither should they be purchased based on their size, since this will waste energy.
• 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.

Here’s how it works: Before you can accurately answer the question of what size tankless water heater you require, you must first determine two things:

1. What is the greatest amount of hot water you require?
2. What is the maximum amount of water per minute (measured in Gallons Per Minute or GPM) that a particular tankless water heater can heat, and by how many degrees?

• It is necessary to establish a preliminary estimate of our maximal hot water requirements at any given point in order to properly design the tankless water heater.
• From 9 p.m.
• to 11 p.m., most families have the greatest demand for hot water.
• That is the time of day when we shower, brush our teeth under a hot faucet, and perhaps even have the dishwasher on.
• We need to keep track of how much hot water we’re using.
• Here’s a handy table that shows how many GPMs are required by different types of water fixtures:

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 (with 100 percent flow and 110°F hot water) and concurrently using two faucets (both with 100 percent flow and 110°F hot water), you’ll need a tankless water heater with at least 5 GPM flow rate.
• It is possible to get anything from 2 GPM to 12 GPM of hot water using a tankless heater.
• How many gallons per minute do you require?
• The ones with a flow rate of 5-10 GPM are the most suitable for the majority of houses.
• As previously stated, the cost of a tankless water heater grows in direct proportion to the capacity of the unit.
• It should be noted that electric tankless hot water heaters are suited for modest water demands up to 8 GPM.

Choosing one of the top gas tankless hot water heaters from this list is recommended for larger requirements (8 GPM or more).

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.
• In Minnesota, for example, the temperature of the input water might be as low as 37 degrees Fahrenheit.

That represents an additional 40 degrees Fahrenheit differential that a tankless water heater must overcome.Calculation in a few words: Consider the following scenario: we have a tankless heater with a maximum water flow of 10 GPM.Because the input temperature is 77 degrees Fahrenheit in Texas, we can really obtain 10 GPM of 110 degrees Fahrenheit water.The heater must heat water from 77 degrees Fahrenheit to 110 degrees Fahrenheit, a difference of 33 degrees Fahrenheit.

In Minnesota, on the other hand, the inlet water temperature is 37 degrees Fahrenheit.In order to heat water to 110 degrees Fahrenheit in Minnesota, a tankless heater must overcome a temperature differential of 73 degrees Fahrenheit, rather than the 33 degrees Fahrenheit difference in Texas.You don’t come from Minnesota or Texas, do you?Here’s an infographic developed for the Rinnai RU160iP SE+ Series 9 GPM tankless water heater that will give you an idea of what the maximum water flow rate is in your state (legal for the United States of America).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.

1. The water pressure is sufficient to run numerous showers at the same time.
2. 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.
3. That is a direct outcome of the temperature differential between the input and outlet.

1. In New York, the heater must contend with an additional 25 degrees Fahrenheit.
2. You will be able to operate two or three showers at the same time using the same heater and the same amount of energy consumption.
3. It’s important to consider the operating costs as well, especially with larger units.
4. You can find out how much power larger electric tankless water heaters consume by visiting this page.

The amount of propane that these on-demand hot water heaters consume is another useful piece of information regarding propane units to read.

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.
• A table containing estimations may be seen below.
• Unfortunately, the confidence ranges are extremely wide.

Those in the Northern United States will require larger units than homes in the Southern United States, for example, as follows:

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

These data are provided just as a point of reference. The size of your tankless water heater is determined by a number of crucial criteria, such as the temperature of the water entering the tank and the amount of hot water you use on a regular basis.

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).
• Power, on the other hand (measured in kW), is absolute.
• 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.

All things considered, you must also consider certain financial calculations, for example.It is advised that you check here to see if a tankless water heater is actually worth the investment (we did some calculations).Let’s take a look at two real-life situations.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.

Second, the number of people who live (and utilize) hot water in your home is taken into consideration.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. When it comes to tankless water heaters, though, things are a little different. 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. You would, roughly speaking, require the following items to replace a 50-gallon water heater: a 10 GPM gas tankless heater or at least a 27 kW electric tankless water heater if you live in the northern part of the United States
• a 7 GPM gas tankless heater or at least an 18 kW electric tankless water heater in the southern part of the United States
• and a 50-gallon water heater replacement kit.

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: 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.
• The tankless heater needs to work extra hard to raise the water temperature to 110°F or 120°F, depending on the situation.

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.As a result, for a family of five in the southern United States, a 7 GPM gas tankless heater or an 18 kW tankless heater should be more than adequate to meet all of their hot water demands.Keep in mind that, especially with larger units, tankless water heater circulation pumps can save you a significant amount of money on hot water.These pumps come in handy when you need hot water from a faucet or shower in a short amount of time.

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.
• During times when we require a large volume of hot water, the electric tankless water heater is activated to provide assistance.

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.

How To Size A Tankless Water Heater

If you are in the market for a new water heater, tankless hot water heaters may be an option to investigate. 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.
• It is possible to determine How To Size A Tankless Water Heater by following the methods 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 the flow rate for each.
• The flow rate is the number of gallons per minute of water flow that you will require.
• 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.

When it comes to hot water faucets, a flow rate of around 0.75 gallons per minute is recommended.The flow rate of the shower head will be 2.6 gallons per minute.Your hot water heater should be able to deliver at least 3.26 gallons of hot water per minute, whichever is higher.Low-flow water faucets and shower heads are available for purchase and installation if you wish to reduce your flow rates.

2.Determine the temperature rise that will be required for your equipment in step two of this procedure.You will need to subtract the temperature of the incoming water from the temperature of the output water.If you do not know the exact temperature of your entering water, you should always presume that it is 50°F or above.This will assist to guarantee that you do not choose a tankless hot water heater that is too small.

1. It is crucial to understand that if you reside in a hotter climate, the temperature of your entering water will be greater.
2. You will want to choose a temperature range of 105 to 115 degrees.
3. If this is the case, you will need to ensure that the tankless water heater has the ability to offer a temperature rise of 55 degrees or greater.

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.
• Determine the flow rates that you will require from your hot water heater in order to guarantee that you can complete the tasks that you have set for yourself.
• Suppose you want to take two showers at the same time, or you want to run many sinks at the same time.

In order to meet your bathroom water requirements, it is advised that you utilize 1.0 GPM.The water from your tankless water heater will be insufficient if you are running two different showers at the same time.Water consumption will be around 4.5 gallons per minute if you need to operate both your washing machine and shower at the same time.You’ll want to be certain that the heater you choose is the appropriate size.

Calculating your water use rates can assist you in selecting the most appropriate tankless water heater for your needs.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.These gas hot water heaters have the ability to swiftly raise the temperature of the water.For more information on How To Size A Tankless Water Heater, contact the Original Plumber right away.They will be able to tell you what size water heater you require and will show you the many alternatives that are available.

1. 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.
2. 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.
3. The installation of a water heater may be complex and risky, therefore it is always a good idea to leave it to the experts.

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

• Last updated on August 25, 2021. Written by Gene Fitzgerald This page may contain affiliate links, so please keep that in mind. If you purchase a product or service after clicking on one of these links, we will get a commission at no additional cost to you. More information about our product review methodology may be found here, as well as our FTC affiliate disclosure. Tankless water heaters allow on-demand access to an infinite supply of hot water. Furthermore, they can reduce your utility bills by more than 30% due to the elimination of standby energy losses, they are about the size of a suitcase and therefore take up less space, and they have a lifespan of up to 20+ years, which is nearly twice as long as the lifespan of a traditional tank-based unit. Tankless water heaters, on the other hand, are restricted in the amount of water they can heat at any given moment. 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. If you go too large, you will end up paying too much. This is why it is critical to have the right size before making a purchase. This purchasing guide will lead you through the process of sizing a tankless water heater and will also throw light on other issues that you should consider when shopping for a tankless water heater. Table of ContentsHow to calculate the size of a tankless water heater Step 1: Calculate the flow rate (in gallons per minute for a tankless water heater)
• Step 2: Calculate the temperature rise
• Step 3: Put it all together
• Video

• Size chart
• Example size chart

• Tankless water heater size calculator
• Frequently Asked Questions
• Tankless water heater installation

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.
2. The needed temperature rise, which is determined by the parameters for the input water temperature and the output water temperature

The amount of hot water you require during peak usage (in gpm, or gallons per minute). Keep in mind that tankless water heaters do not store water, but rather heat it as it runs through the system.
The needed temperature rise, which is calculated by the parameters for the input water temperature and the output water temperature.

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

• Begin by determining your peak hot water consumption 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. Then sum up all of their flow rates together. 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.

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.
• This will provide you with a general notion of how much flow is required.

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.Then, for each outlet, compute the flow rate using the following formula: Filling a bucket takes 60 seconds at the current flow rate.Use this formula instead of filling an entire gallon per outlet if you don’t want to squander a full gallon each outlet: 15 seconds are necessary to fill a 14-gallon bucket at the current flow rate.

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.
• Now, this makes a significant difference in how hard a tankless water heater needs to work in order to get water up to the appropriate temperature temperature.

Assume you reside in Michigan, where the average feed water temperature is 40 degrees Fahrenheit.And you want the output temperature to be 110 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.A water heater installed in a home in Texas with 70 degrees Fahrenheit inlet water temperature must warm up the water by as little as 110 degrees Fahrenheit plus 70 degrees Fahrenheit equals 40 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.
• If you want to save money on your hot water bill, you should purchase a unit that either matches or surpasses your peak demand.
• 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.

It is common for certain organizations to overestimate the capabilities of their technology…Are you ready to take the next step?Please read the following reviews to choose the best electric tankless water heater for your requirements!!

Video

Do you prefer video? Take a look at this:

Size Chart

• If you look at a few size charts, you will immediately discover that the use of gas or electricity makes a significant difference.
• In general, tankless gas water heaters are more powerful than electric water heaters, which means that they can produce more gallons per minute (gpm) at the same temperature increase.
• As an illustration: If you want a temperature rise of 70 degrees Fahrenheit, a big tankless gas water heater can provide 5.0 – 5.5 gallons per minute at that temperature.
• The biggest electric unit (36 kW) produces a maximum flow rate of little more than 3.0 gpm.

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?
• Once again, there is simply insufficient information to provide a credible response.

It is dependent on the number of bathrooms and water-using appliances you have, as well as the temperature rise necessary.You should either follow the instructions in this sizing guide or use our sizing calculator to determine your size.3.Approximately how many tankless water heaters are required?

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).In general, one tankless gas water heater should be sufficient to meet the needs of a medium-sized family or house.Electric tankless water heaters are ideal for households with fewer people or for tiny flats.At the event of extremely high demand, consider installing two or more heaters, either at the point of use so that they may operate independently of one another or in a central location so that they can operate in tandem as a single unit.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.

1. Please share your ideas or questions regarding how to size a tankless water heater in the comments section below.
2. Thank you for your time!
3. Gene Fitzgerald’s biographical information Gene Fitzgerald has been a part of the BOS family since its inception.

1. 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.
2. Gene enjoys reading books on philosophy and social topics, producing music, and going on hikes when he is not at BOS.
3. Find out more about.