What Size Water Heater Do I Need Calculator

What Size Water Heater Do I Need For My House?

Residential water heaters are typically available in capacities ranging from 40 to 100 gallon tanks. Typically, most homeowners find that a 40 or 50 gallon hot water tank is the most appropriate size for their needs and budget. Therefore, they are the two most commonly used dimensions in construction. Every household, on the other hand, has varied water consumption requirements. This is dependent on the amount of people that live in the house, the frequency with which water is used, and whether or not the water is used during peak hours.

On a practical level, this may mean that you run out of hot water while in the middle of your shower.

How To Determine The Size Of A Water Heater Tank

Residential water heaters are often available in capacities ranging from 40 to 100 gallons. A 40 or 50 gallon hot water tank is usually the best choice for most homes, depending on their requirements. The two most commonly installed sizes as a result are as follows: Individual water consumption needs vary from family to family, nevertheless. In this case, it is dependent on how many people live in the house, how frequently the residence uses water, and how much water is used during peak hours.

On a practical level, this may mean that you run out of hot water while you are in the middle of your shower.

Tank’s FHR (1st Hour Rating)

The FHR rating tells you how many gallons of water a heater can generate in an hour at a specific temperature. This number may be found on the Yellow Energy Guide Label on the back of the label. (See below for further information.) As time passes, the water will continue to cool down at a rate determined by how rapidly you are using it up. Once this occurs, it will take a specific length of time for the heater to recover to its full FHR capacity. This time varies depending on the equipment, and it should be taken into mind while selecting a hot water heater.

Your Peak Hour Demand

Your household’s consumption of hot water at the busiest time of the day for your family is represented by this figure: Consider the following scenario: you’re having 2-3 showers at the same time while doing laundry and running the dishwasher. (See below for information on how to determine peak hour demand.) Keep in mind that taking a shower consumes the most water of any activity. This implies that your busiest hour will be at the time when the most of the individuals in your home are showering, especially if a number of them are doing it at the same time.

During the same time that I am out of the house in under 5 minutes, my teenage daughter and wife both take a 30-40 minute shower every day!

Remember that the size of the tank will have a direct influence on its cost (a larger tank will cost more money). If you are working with a limited budget, you have even more incentive to take the time to figure out what tank capacity would work best for you.

How To Estimate Your Peak Hour Demand

Your household’s consumption of hot water at the busiest period of the day for your family is represented by this figure. Consider the following scenario: you are taking 2-3 showers at the same time while doing laundry and running a dishwasher. To determine peak hour demand, check the section below. You should be aware that having a shower consumes the most water. Therefore, your peak hour will occur around the time when most individuals in your home are having a shower, particularly when many of them are doing it at the same time.

In contrast to me, my teenage daughter and wife both take a 30-40 minute shower every day, while I am out in less than 5 minutes.

Take into consideration the fact that the size of the tank will have a direct influence on its cost (a larger tank will cost more money).

Activity Average Gallons of Hot Water Per Usage (x) Times Used During 1 Hour (=) Gallons Used in 1 Hour
Shower 10 x =
Shave (0.5 gallons / min) 2 x =
Hands/Face Washing (2 gallons / minute) 4 x =
Hair Shampoo (2 gallons / minute) 4 x =
Hand Dishwashing (2 gallons / minute) 4 x =
Food Prep (2 gallons / minute) 4 x =
Automatic Dishwasher 6 x =
Clothing Washing Machine 7 x =
Total Peak Hour Demand

Water Heater Size Based On Number Of People In A Household

Here is a simple reference table that you may use to find out the appropriate tank capacity for your home if you don’t want to deal with any complicated calculations.

Family Size Water Heater Capacity
1-2 23-36
2-3 36-46
3-4 46-56
5-6 56-80
6-7 80-100
7 or more 100 or more

Here is a simple reference chart that you can use to find out the appropriate tank capacity for your home if you don’t want to bother with any math.

High Hot Water Usage Demand

How would you know if the demand for hot water in your home is really high? It’s simple: if you have more than 2-3 appliances that utilize hot water at the same time, you’ll need a larger hot water tank than the one recommended for your home. If this is the case, you might consider installing a unit that is one size larger than your current household size. For those of you who have the practice of operating only one hot water appliance at a time, a tank of the average size recommended for the number of people living in your home will be more than adequate to complete the work in your household.

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 demand-type
  • Solar water heating systems
  • Storage and heat pump (with tank) water heaters
  • And other options.

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.

  • This is the intended flow rate that you’ll need for the demand water heater that you’ve purchased.
  • 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.
  • (or liters per minute).
  • Installing low-flow water fixtures can help to lower flow rates.
  • Assume that the entering water temperature is 50 degrees Fahrenheit (10 degrees Celsius) unless you know differently.
  • Water should be heated to 120 degrees Fahrenheit (49 degrees Celsius) for the majority of applications.
  • For dishwashers without internal heaters and other similar uses, you may wish to heat your water to 140 degrees Fahrenheit (60 degrees Celsius).
  • When the water temperature reaches 140 degrees Fahrenheit, use caution since it raises the risk of scorching.
  • 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.

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

Basic system sizing entails calculating the total collector area and storage capacity required to satisfy 90 percent to 100 percent of your household’s hot water demands throughout the summer. 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.

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. For further information on these calculations, please see thesolar water heaterspage.

Sizing Storage and Heat Pump (with Tank) Water Heaters

You should use the water heater’s first hour rating to determine the correct size for your home – this includes heat pump water heaters with tanks. 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 labeled as “Capacity (first hour rating)” in the upper left corner of the EnergyGuide label, which is displayed on the screen.

The first hour rating may also be found in product literature provided by the manufacturer.

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.

Decide what time of day (morning, lunch, or evening) your household consumes the most quantity of hot water. It’s important to consider the quantity 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 by using the worksheet below.

Please keep in mind that the worksheet does not provide an estimate of total daily hot water use.

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 information published on the internet, including government sources. Various calculators are available on some water heater manufacturer websites, which are depending on the duration of the use case and other criteria.

Water Heater Sizing Calculator: What Size Water Heater Do I Need?

It is not always simple to determine the proper size of a water heater. It is very typical for people to make the following mistakes when selecting a water heater capacity for a household of 2, 3, 4, 5, or 6.

  1. Purchasing a water heater that is too small (undersizing). If the capacity of your water heater is insufficient, you will most likely run out of hot water while bathing. An illustration of a water heater that is too small: For a household of five, a 30-gallon water heater is being installed. That equates to more than half of the water heater capacity that you actually require. Purchasing a water heater that is too large (oversizing). If your water heater’s capacity exceeds your hot water requirements, you will incur unnecessarily higher water heater expenses. An example of a water heater that is overly large: Water heater installation for a two-person family of sixty-gallons. That is almost 20 gallons more than you require, and you have unnecessarily spent an extra $150 dollars on the heater as well as wasted space.

Neither of these mistakes can be made if you know how to correctly select the appropriate water heater capacity for your hot water requirements. The problem is this: When it comes to sizing your water heater, you only have one chance. You don’t want to make the mistake of purchasing a unit that is either too large or too tiny. That is what we will be looking at today: how to choose the appropriate water heater size for your home. This comprises elements that raise or decrease the amount of water heater capacity that is necessary (size of your family, hot water needs, etc.).

On top of that, we created a ‘Water Heater Sizing Calculator’ to make sizing a water heater as simple as possible.

The following is an example of what the results look like (screenshot): This ‘Water Heater Sizing Calculator’ may be found lower down the page.

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Let’s start by being familiar with terminology such as “first hour rating,” “water heater capacity,” and “peak hour hot water demand” when it comes to water heater selection.

How To Estimate The Size Of A Water Heater You Need?

The capacity rating of a water heater is a critical specification that allows us to properly size a water heater. Water heaters with capacities of 30 gallons, 40 gallons, 50 gallons, and 60 gallons are discussed. The ‘water heater capacity rating’ is the number of gallons that the water heater can hold. This is frequently referred to as a “first hour rating.” When starting with a tank full of hot water, it is the volumetric quantity of hot water that a heater can provide within the first hour of operation.

  • Simple.
  • Simply look at the label to determine the real size of your water heater.
  • Consider the following scenario: From 10 PM to 11 PM, three persons take a shower.
  • That implies you’ll need a water heater with a capacity of at least 60 gallons.
  • The size of your family can be approximated by this number.

As an illustration, a family of five will need less hot water than a family of three. It is important to note that after the first hour (when we started with a tank full of hot water), the output of a water heater is influenced by three key elements. These are the ones:

  1. Heat source (gas versus electricity)
  2. Water heater tank capacity
  3. Heat source (burner (gas water heater with tank) or element (electric water heater with tank)
  4. Water heater tank capacity (electric water heater with tank). Electric water heaters are the topic of discussion. The size of the aforementioned heat source, that is, the size of the burner or the size of the element

Of course, after the first hour, any water heater will be able to provide less hot water in the 2nd, 3rd, and so on hours after the first. For example, if you have a 50-gallon water heater with a first-hour rating of 50 gallons, you will receive 50 gallons of hot water during the first hour of operation. However, it is likely that you will receive far less than 50 gallons of hot water in the second hour (about 16 gallons on average in this case). To determine how much hot water we will require during our peak showering hours, we must first determine how much hot water we will require during the preceding rule of thumb for sizing a water heater.

Estimating Peak Hour Demand: This Is The Key Step

The ability to create hot water in the 2nd, 3rd, and so on hours after the 1st hour is unavoidable with any water heater. A 50-gallon water heater (whose first hour rating is 50 gallons) will provide you with a water heater capacity of 50 gallons during the first hour. Nonetheless, you will most certainly receive somewhat less than 50 gallons of hot water during the second hour (about 16 gallons on average in this case). To determine how much hot water we will require during our peak showering hours, we must first determine how much hot water we will use during the rest of the day, according to the rule of thumb mentioned before.

  • Showering requires 20 gallons every shower
  • Brushing teeth requires 0.5 gallons
  • Hand washing requires 3 gallons
  • Shaving requires 2 gallons. Top-loading clothes washers hold 25 gallons of water
  • H-Axis clothes washers hold 15 gallons of water.

In reality, here’s an example of how to estimate the peak hot hour requirements in advance. Consider the following scenario: you have a four-family home with two bathrooms. The family takes a shower from 10 PM to 11 PM, one person shaves, and all four family members brush their teeth at this time. Hot water consumption totals 320 gallons (3 showers) plus 12 gallons (shaving) plus 40.5 gallons (cleaning teeth) equals 64 gallons of use. The capacity of your water heater must be at least 64 gal.

  • In this situation, a 70-gallon water heater is widely available, but a 60-gallon water heater will most likely be too little for your needs (undersized).
  • If you use this ‘peak hour demand’ rule of thumb to predict your hot water requirements, you will have a little wiggle room in the higher direction.
  • That implies that if you estimate your peak hour hot water use to be 64 gallons, you may get away with a 70-gallon water heater.
  • In practice, if you anticipate that you use 64 gallons of hot water during peak hours, you should purchase a water heater with a capacity of 64 gallons or greater.
  • It is important to note that undersizing a water heater will be more problematic than oversizing a water heater in most cases.

Don’t be concerned if all of this appears to be a bit complicated. There is a more straightforward method of determining the size of a water heater. It is founded on three fundamental principles:

  1. As an illustration of how to estimate the peak hot hour requirements in practice, consider the following. Say you had a four-family home with two bathrooms. What would you do? 3 individuals shower, 1 person shaves, and all 4 family members brush their teeth from 10 PM to 11 PM during this time period. Hot water use totals 320 gallons (3 showers) plus 12 gallons (shaving) plus 40.5 gallons (cleaning teeth) equals 64 gallons of water. The capacity of your water heater must be at least 64 gal. in order to accommodate this requirement. If you have this situation, a 70-gallon water heater should be easily obtained
  2. Nevertheless, a 60-gallon water heater would most certainly be insufficient (undersized). Most of the time, an 80-gallon water heater is too large for a household of four. It is possible to have some wiggle room in the upper direction if you calculate your hot water demands using the “peak hour demand” rule of thumb. Water heater capacity can be increased by around 10% to 15% beyond that calculated. In other words, if you estimate your peak hour hot water need to be 64 gallons, you may acquire a 70-gallon water heater. The capacity of your water heater should not be reduced, though. On the other hand, if you figure that you use 64 gallons of hot water during peak hours, you should purchase a water heater that holds 64 or more gallon capacity. Never, ever get any smaller than that! It is important to note that undersizing a water heater will be more problematic than oversizing a water heater in most situations. Don’t be concerned if this all appears to be a bit complicated. Choosing the proper size for a water heater could not be much more straightforward. These are the three concepts that underpin it:

Based on these three concepts, we can make an educated guess as to what size water heater you will require based on the size of your family:

Water Heater Sizing Calculator (Based On Family Size)

‘What Size Water Heater Do I Need’ is a calculator that will give you an approximate estimate of the size of the water heater you will need for your home. To use the water heater capacity calculator, simply enter your family size and hot water requirements (below average, average, or above average), and the water heater capacity calculator will dynamically calculate the water heater capacity in gallons: On the basis of this technique of water heater sizing, you may get an approximate idea of what size water heater you need for your family:

Family Size Water Heater Size (Gallons)
Family of 1 25 Gallons
Family of 2 35 Gallons
Family of 3 45 Gallons
Family of 4 55 Gallons
Family of 5 65 Gallons
Family of 6 75 Gallons

When purchasing a water heater, keep in mind to look for the Energy Star logo as well. Water heaters that are energy efficient pay for themselves in the majority of situations. You may learn more about the requirements for receiving an Energy Star designation by visiting this page. We hope you found this information to be useful.

Water Heater Size Calculator

The second highest energy expense in your house is the cost of heating water. Knowing how much water your family uses in the first hour can assist you in selecting the appropriate size heater. When you get a water heater that is too tiny, it will wreak chaos in your home, but when you purchase a water heater that is too large, you will squander money both in the original purchase and in the ongoing expenditures of keeping all of that water hot around the clock, every day of the year. If you’re shopping for a new water heater, the first-hour rating (FHR) is the most crucial characteristic to look for.

  • Take a moment to estimate the amount of hot water your home will use during the busiest one-hour period of any given day on a typical schedule.
  • Be sure to account for growing children and other factors that might raise your water use.
  • When shopping for a new heater, be sure to look at the FHR (first hour recovery) rating first.
  • Even if your shower head is very recent, it is still possible to find the gallons per minute water consumption rating etched into the metal of the fixture.
  • You may determine your family’s first-hour capacity for a water heater by calculating the average water consumption (in gallons per minute) for each fixture used during the one-hour period when water usage in your home is the highest.
  • Pouring water into a tub may be measured by placing an empty gallon milk jug beneath the faucet spout, turning on the faucet handles as far as they will go and timing how long it takes to fill the tub to its maximum capacity.
  • If it takes 40 seconds to fill the jug, the rate of flow is 1.5 gpm, according to the manufacturer.

Warning Regarding Water Heater: The customer has been informed that the water heater should be kept at 120 degrees, as recommended by the manufacturer and in accordance with Gas Appliance Manufacturers Association (GAMA) guidelines.

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Chart for determining the size of a water heater Learn how to properly size a water heater before making a purchase to prevent common mistakes made by homeowners. The size guide, advice, calculators, and chart will assist you in selecting the most appropriate gas- or electric-powered tank-type model, including tankless, to ensure that you always have enough hot water for a dependable and enjoyable shower. Choosing the proper size for your water heater is critical because if you get a little unit, it will run out of hot water quickly, and if you purchase a larger unit than is necessary, you will be charged extra for hot water that you will not use.

There are also models that are high-recovery and ultra-efficient, so you will have a wide range of options to choose from.

Highlights

  • Why it is vital to properly size a water heater
  • What to think about – Sizing considerations
  • How to choose a heater depending on the specifications of the heater
  • In the form of a table showing average usage and peak hour demand
  • Choosing the appropriate size for a tankless
  • Calculators for sizing water heaters

Why sizing a water heater is important

A water heater is the second-largest energy user in the home, after space heating, and with the growing cost of energy, water heating might have a substantial influence on your household’s finances. Before purchasing a new unit, it is necessary to consider the operational costs, which include more than just the price of gasoline and the heater. A common query I hear, as well as a common theme in many reviews, is “the heater does not produce enough hot water” or “there is no hot water after 15 minutes of using the heater.” When purchasing a new unit, the above-mentioned considerations should be taken into consideration (and I mean seriously).

must understand how to correctly size a water heater so that you don’t wind up spending extra money or having to struggle with chilly showers and unfinished washing.

What to consider when sizing a tank-type water heater?

A water heater is the second-largest energy user in the home, after space heating, and with rising energy prices, water heating might have a big influence on your budget. The operational costs of a new unit must be considered in addition to the costs of fuel and heater when making a purchase decision. One of the most often asked problems I receive, and which can also be seen in many customer evaluations, is “the heater is not producing enough hot water” or “there is no hot water after 15 minutes of using it.” When purchasing a new unit, the above-mentioned considerations should be taken into consideration (I mean seriously).

how to appropriately measure a water heater so that you don’t have to pay extra money or suffer with the inconvenience of cold showers and undone laundry

  • Is there a total of how many persons dwell in the household? How many children and teens are there? Teenagers have a tendency to use a lot of hot water in their daily lives. Taking into consideration any regular guests you have or want to have, as well as their overnight stays (grandparents, for example), is also crucial. Count the number of plumbing fittings in a house, including dishwashers, laundry washers, notably big baths, whirlpools, and other such items
  • It would be interesting to know how many showers would be utilized at the same time. What is the length of the longest bathtub

The tank capacity should be the same as or more than the tank capacity if you have a whirlpool tub.

  • What is the frequency with which hot water is consumed? Its most frequent usage is in the early morning before work and school, in the evening before bed, or at any other time of the day. What is the temperature of the entering (groundwater) water? The temperature of groundwater is affected by factors such as location, elevation, and time of year (climate). Using amapt, you may find out what the average temperature is in your location. In addition, location is significant since groundwater or entering (inlet) water, for example, is cooler in northern areas than it is in southern parts

Which hot water use patterns are prevalent? Its most frequent usage is in the early morning before work and school, in the evening before bed, or at any other time of the day or night When it comes to groundwater, what is the temperature of the incoming water? Location, elevation, and time of year (climate) all have an impact on the groundwater temperature. In order to find the average temperature in your location, you can use the amapt program. In addition, location is significant since groundwater or entering (inlet) water, for example, is cooler in northern areas than it is in southern parts; and

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How to size a water heater and select the right model based on the product specifications

The following crucial statistics will be found in the specifications offered by the manufacturer while looking for heaters. They are: power consumption, efficiency consumption during peak hours of demand, first hour delivery, and recovery rate. As you examine the technical data, you get more familiar with the many types on the market and how to correctly size a water heater for your needs. The quantity of electricity (in Watts) or natural gas (in BTU) utilized for water heating in one hour is referred to as the power or input.

The Peak Hour Deliverymeasures the maximum quantity of hot water (measured in gallons per hour – GPH) provided by a water heater at the busiest period of the day.

The Recovery Rateis the quantity of water (in gallons per hour) that can be raised by a single heater when the temperature is raised by 60 degrees Fahrenheit.

When comparing electric and gas units, gas models offer a greater First Hour Delivery, which allows the tank to be smaller than the tank of an electric unit while generating the same quantity of hot water as an electric unit.

Table of the average consumption and peak hour demand

The following computation is based on a family of four members:

Application Average consumption (gallons) Peak time usage(in one hour period) Used Hot Water (gal.)
Shower 20 4 80
Automatic Dishwasher 14
Clothes washer 32
Hand dishwashing 4 1 4
Shave 2 1 2
Food preparation 4 1 4
House cleaning 6
Hand washing 2
Hot water demand in the peak time (gal.) 90

Water heater sizing chart as per manufacturers’ recommendations

Family size (of people) Peak demand (gallons) regular/high demand
2 45-55
3 55-65
4 65-75
5 75-85
6 85-100
7 100 or more

Every water heater is equipped with an Energy Guide label that displays the capacity for peak hour demand, commonly known as the First Hour Rating, of the water heater (FHR). If you’re in a shop and didn’t have time to study how to size a water heater, you may use the FHR value instead — the higher the number, the better the water heater’s performance. It is sometimes worthwhile to consider purchasing a water heater with smaller tanks and better recovery rates, rather than one big unit, rather than one large unit.

Sizing a tankless water heater

Water heaters using tankless technology, as opposed to tank-type ones, do not store hot water in the tank. They make use of a heat exchanger, in which water is heated as it passes through – on demand. In order to answer the question “how large a water heater do I need,” we take a different technique when measuring and trying to determine the appropriate size. The following points should be taken into consideration: What is the flow rate (in gallons per minute)? When running two fixtures at the same time, one with a flow rate of 0.5 GPM and the other with a flow rate of 1 GPM, the tankless water heater should have a minimum flow rate of 1.5 GPM.

What is the flow rate of each device, as well as the total volume of each device?

What is the increase in temperature?

It’s important to remember that the temperature of entering water varies depending on the place and environment.

The majority of manufacturers will supply a table or graph illustrating a range of water flows in response to a range of temperature increases. Tip: To find out the temperature of groundwater in your area, look at this map of temperatures.

  • Bathroom: 0.5-1.5 GPM
  • Kitchen: 1.5 GPM
  • Shower: 1-2 GPM
  • Dishwasher: 1.5 GPM
  • Clothes washer: 2 GPM
  • Bathtub: 4 GPM

Sizing tools and calculators

  • State Industrial Calculator
  • Noritz Calculator and Flowrate
  • Rinnai Calculator
  • State Industrial Calculator

Conclusion

All of the water heater sizing recommendations in the preceding text are beneficial to homeowners who are purchasing a new water heater or replacing an existing one. Always keep in mind your future family’s hot water requirements; for example, if you frequently run out of hot water, your family is growing, or you want to install some additional fixtures, purchasing a larger tank is a smart option. Sizing tank-type water heaters is dictated mostly by their tank capacity and recovery rate (measured in gallons per hour, or GPH), whereas tankless water heaters are measured by their hot water flow rate (measured in gallons per minute, or GPM).

Related

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. See our product review method in further detail, or read our FTC affiliate disclosure for more information. 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.

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
  • 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. 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.
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

*Products that have been WaterSense-certified Please keep in mind that older fittings are more likely to have higher flow rates than more recent fixtures. Please note that we did not include flow rates for washing machines and dishwashers, as you can see in the table. Why? Because obtaining solid information on this topic was extremely difficult. There are conflicting reports about how many gallons per minute are being produced. Instead, you might run each appliance independently while keeping an eye on the timer and water meter.

While we’re on the subject of measurement, you may use a 1-gallon bucket to track how long it takes your shower head, kitchen faucet, bathroom taps, and other fixtures to fill it.

Use the following formula to compute the flow rate for each outlet after that.

Flow rate = 15 / Number of seconds necessary to fill a 14-bucket trough

  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.)

See also:  When To Replace Water Heater
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?

  1. It is dependent on the number of bathrooms and water-using appliances you have, as well as the temperature rise necessary.
  2. 3.
  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).
  4. Electric tankless water heaters are ideal for households with fewer people or for tiny flats.
  5. 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.
  6. Thank you for your time!
  7. 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.

How To Size A Tankless Water Heater: Use Our Sizing Calculator

In the event that you are just getting started on your quest to get a tankless water heater, you are most likely asking yourself, “What size tankless water heater do I need?” When it comes to purchasing a tankless water heater, this is perhaps the most crucial question to ask. People are accustomed to thinking in terms of capabilities. For example, a hot water tank for 5 persons will necessitate the purchase of a tank that is at least 60 gallons in size. However, because tankless water heaters provide limitless hot water, you won’t have to worry about running out of hot water.

Flow rate is a measure of how much hot water you will want in a certain amount of time, and it is measured in Gallons Per Minute (GPM) (GPM).

So let’s get this party started!

How Many Gallons Per Minute (GPM) Do I Need?

For the purpose of calculating your GPM, you must first identify which fixtures you can reasonably expect to be running at the same time. Then add up how much hot water (in terms of flow rate) is consumed by each individual fixture. Allow us to use the morning as an example because it is the time of day when most individuals are showering or doing laundry. Consider the following scenario: you have a two-bedroom, two-bathroom home with four people. You have two showers going in the morning, and someone has placed a load of clothes in the washer at the same time.

  • A shower has a flow rate of how many GPM?
  • Alternatively, how about a washing machine?
  • Alternatively, you may refer to the useful cheat sheet provided below to get an idea.
  • By the end of the week, you will have identified some trends and will be able to determine when your peak water demand occurs and how many GPM your on demand water heater will require to meet that demand accurately.

Tankless Water Heater Sizing Calculator

After you’ve written down the maximum number of appliances you use on a typical week, enter the information for those fixtures into our unique tankless water heater sizing calculator to get the appropriate size.

Fixture Type Flow Rate (GPM) Qty Total for Fixture Type
0 GPM
0 GPM
0 GPM
0 GPM
0 GPM
0 GPM
Total Flow Rate 0 GPM

You should have the whole GPM that you require for a tankless water heater at this point in time. Having discussed GPM, let’s move on to the considerations that go into determining what size inline water heater you require. First and foremost, you must comprehend what temperature rising entails. Temperature increase is just the difference between the temperature of the entering water and the temperature you desire to achieve. Your faucets should be set to a temperature of 110 degrees Fahrenheit in most cases.

When you see the GPM rate of a tankless water heater, you are looking at the best case situation.

You will have an infinite supply of lukewarm water if the GPM you want is greater than what the tankless water heater is capable of producing. This is why selecting the proper size tankless water heater is so critical.

Determining Your Temperature Rise

To figure out how much your temperature will climb, you must first know the temperature of the water that is entering your home. In addition, this is based on groundwater temperatures, which will differ significantly depending on where you reside in the United States. See the groundwater temperature map to obtain a broad sense of the temperatures you may expect based on where you reside in order to plan ahead of time. If you want real-time temperature information, you might check this interactive map from the United States Geological Survey.

Simply take the temperature that you anticipate your incoming water to be based on the graph above and multiply it by two.

This represents an increase in your body temperature.

How Big of a Tankless Water Heater Do I Need?

To figure out how much your temperature will climb, you must first calculate the temperature of the water that is entering your house. Groundwater temperatures, which can vary significantly depending on where you reside in the United States, are taken into consideration. To get a basic sense of what temperatures to expect based on where you reside, have a look at the groundwater temperature chart shown below. If you want real-time temperature information, you can check this interactive map from the United States Geological Survey website.

Simply take the temperature that you anticipate your incoming water to be based on the graph above and multiply it by 100.

You’re experiencing a spike in temperature.

How Big of a Water Heater Do I Need for Radiant Heat

When it comes to radiant floor heating and domestic hot water demands, water heaters are a popular choice among homeowners. The question is, though, how much of a water heater do you require for radiant heat. When you have a radiant floor installed, keep in mind that the tankless water heater will have to operate continually to keep up with demand. In addition to your typical home water use, you may want to think about upgrading to a greater GPM. Furthermore, because your water heater is expected to survive just 5-10 years if it is being used for radiant heat, we believe it is prudent to consider installing an aboiler in conjunction with your hydronic radiant heating system.

In order to figure out how much of a water heater you’ll need for radiant heating, you’ll need to figure out how much heat you’ll lose.

It actually depends on your specific scenario, such as how old your house is, and other factors.

The water heater listed below is one that we suggest for radiant floor heating.

It is a model with 11 GPM and 199,000 BPU, which is suitable for the majority of families. And don’t forget that radiant heating thermostats will assist you in keeping your system in good working order. Rinnai Water heater with a flow rate of 11 GPM

  • Limitless Hot Water: Take use of an unlimited supply of hot water throughout the house
  • Efficiencies in terms of energy and space: A space-saving design helps to preserve energy while also conserving space. A strong, efficient hot water flow rate of up to 11 GPM is achieved by optimal water pressure. Instant Heating: ThermaCirc360 technology gives quicker hot water with a single turn of the water heater. Guaranteed to Last: 15-, 5-, and 1-year home heat exchanger warranties are available.

How to Choose a Tankless Water Heater

There is a lot more to consider than simply the size of the tankless that you should be aware of. To make your selection, there are several options. Each has a certain function for which it has been conceived and constructed. Here are a few things to think about before making a purchase.

Gas vs Electric

In my opinion, the vast majority of houses should make use of a gas tankless water heater. Because they produce the greatest GPM, gas tankless water heaters are the best choice for most houses. In order to provide hot water to the entire house with only one unit, this is the most efficient option to consider. When you don’t have access to natural gas or propane, electric units are an excellent alternative. The initial cost of electric tankless heaters is a significant advantage. They are far less expensive to purchase than a gas-powered variant.

How Much BTU?

Most families, in my view, should switch to a gas tankless system. Because they produce the greatest GPM, gas tankless water heaters are the best choice for most households. This would be the best option if you want to provide hot water to the entire house from a single unit. When you don’t have access to natural gas or propane, electric units are a fantastic option to consider. The low initial cost of electric tankless heaters is a significant advantage over other heating options. In comparison to a gasoline-powered vehicle, they are far less expensive to purchase.

Whole House vs Point Of Use

The majority of individuals will choose a single unit that will offer hot water for the entire house. This makes the most sense in a variety of situations. Although there is a strong argument for having numerous tiny tankless water heaters at each point of usage, this is not always the best option. Example: If you have two bathrooms, you may install a unit under each sink and it will offer hot water on demand for the sinks and showers in each bathroom, as well as for the washing machine in the second bathroom.

These point-of-use tankless water heaters may deliver a few GPM, which is sufficient for the majority of applications, and they are not nearly as expensive to purchase or install as conventional tankless water heaters.

Installation

Costs associated with installing a whole-house gas tankless heater can be prohibitively expensive, and this factor may influence the decision on which type of tankless heater to purchase. The distance between the heater and the fixture, as well as the location of the venting, are all elements that influence the cost of the project. In other circumstances, you may have to drill through a brick wall, which raises the expense of the project. You can find out all you need to know about your installation choices by clicking on that link.

Because the heating element is a form of anode, there is no need for an exhaust.

Is it possible to install a tankless water heater on your own?

In the vast majority of circumstances, you most certainly can. It’s simply a matter of following the directions provided. However, it may be beneficial to contact a professional to ensure that you do not invalidate your guarantee by installing the product incorrectly.

FAQ About Tankless Water Heaters

Is it possible for a tankless heater to run out of hot water? Technically, no, it is not possible for it to run out of hot water. When you have a tankless water heater that is the proper size for your hot water need, you will have an unlimited supply of hot water. Accordingly, if your tankless heater cannot keep up with your demand, you will have an infinite supply of tepid water since it will have to reduce the temperature to maintain the required level of heat output. This is why it is critical to get the most appropriate equipment for your requirements.

  1. They do not, in fact.
  2. A hot water recirculating pump, on the other hand, will be required if you wish to have immediate hot water.
  3. With proper care and annual cleaning of the heat exchanger, you can expect your tankless water heater to last for at least 20 years or more.
  4. Is it possible to use a tankless hot water heater in conjunction with a well?
  5. Additionally, when dealing with hard water from a well, a filter is recommended.
  6. The Takagi T-H3-DV-N, which provides a massive 10 GPM at the lowest possible price, is by far the most affordable option for the highest GPM.
  7. If you intend on operating at least two showers and a faucet during peak hours, a household of five in the Southern United States would require a 9 GPM gas tankless heater.
  8. It’s always better to be a bit too big than it is to be a little too little.

Are Tankless Water Heaters Worth It?

It is possible that after sizing a tankless water heater and considering your requirements, you will conclude that a tankless water heater is not the best option for you. After all, they are not suitable for everyone. When the circumstances are favorable, a tankless water heater is the most cost-effective option. If you have read poor reviews, it is likely that you are dealing with someone who did not adequately examine their demands and ended up with a product that did not provide the GPM they need.

One of the first questions you should ask yourself is what size tankless water heater you will require.

Nick Lopresti is the creator of YourH2Home and a well-known specialist in the field of home renovation. He has years of expertise writing on a wide range of home improvement issues, the most of which are related to plumbing and water systems.

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