How Big Is A 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.

Step 2:

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

Step 3:

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

Flow Rates

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

Fixture

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

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

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

Other Sizing Notes

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 through gas-fired demand water heaters and 2 gallons per minute through electric water heaters allows for a 70°F temperature rise in the water. 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:

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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. You can read his rants here, or you can listen to him whine about Austin traffic on Twitter at @Bukowsky. You can also follow him on Facebook.

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

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

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

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

A tankless water heater with a minimum flow rate of 5 GPM and a maximum temperature of 110 F will be required if you are having a shower (with 100 percent flow and 110 F hot water) and concurrently using two faucets (with 100 percent flow and 110 F hot water). 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 rises in direct proportion to the capacity of the unit.

Keep in mind that electric tankless hot water heaters are best suited for small water demands up to 8 GPM. If you have a larger need (8 GPM or more), you should choose one of the finest gas tankless hot water heaters available.

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.

  • That represents an additional 40 degrees Fahrenheit differential that a tankless water heater must overcome.
  • Because the input temperature is 77 degrees Fahrenheit in Texas, we can really obtain 10 GPM of 110 degrees Fahrenheit water.
  • In Minnesota, on the other hand, the inlet water temperature is 37 degrees Fahrenheit.
  • You don’t come from Minnesota or Texas, do you?
  • 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.
  • 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.
  • In New York, the heater must contend with an additional 25 degrees Fahrenheit.
  • It’s important to consider the operating costs as well, especially with larger units.
  • Another useful piece of information about propane units is how much propane is consumed by these on-demand hot water heaters.

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

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

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 afamily of 2? 6-8 GPM 10-18 kW
What size tankless water heater do I need for afamily of 3? 7-9 GPM 15-23 kW
What size tankless water heater do I need for afamily of 4? 8-10 GPM 20-28 kW
What size tankless water heater do I need for afamily of 5? 9-11 GPM 25-34 kW
What size tankless water heater do I need for afamily of 6? 11+ GPM 34+ kW

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).

  1. 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.
  2. Check here to see if investing in an energy-efficient tankless water heater is truly worth it (we performed some calculations).
  3. 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.
  4. What size tankless water heater would be appropriate for a household of five, for example.

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

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

Instead of storing hot water, the tankless heater’s strong heating exchanger warms the water as it is needed, up to a particular maximum GMP limit, depending on the model.

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

As a result, Rinnai, the world’s leading manufacturer of gas tankless heaters, provides a broad range of models ranging from 7 GPM to 11 GPM: Rinnai’s gas tankless versions are available in a variety of sizes. As previously said, they are considered to be the top gas tankless water heater brand.

Please keep in mind that this is simply an approximate estimation. The prudent course of action is to get a tankless heater that is somewhat more powerful than the anticipated need. It is preferable to be safe than sorry.

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

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

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.

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

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

How Many Tankless Heaters Do I Need?

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

Alternatively, you might utilize two units for different parts of the home, one for one section and another for the other section of the house.

I hope this has been of assistance.

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

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

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

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

Gallons of Hot Water You Need for a Tankless Water Heater

The first thing you’ll need to think about is how much hot water you’ll require from your tankless heater. In most cases, we refer to this as “sizing,” although you will not be using dimensional measures to determine the appropriate size for your tankless water heater. Instead, you’ll need to pay attention to two separate metrics: the flow rate and the temperature rise (or decrease).

Tankless Water Heaters GPM Flow Rate Explained

When choosing a tankless water heater, the first thing to consider is how much hot water you will require. However, you will not be using dimensional measures to figure out the size of the tankless water heater, as is customary in the industry. The flow rate and the temperature rise, on the other hand, are two separate metrics that must be taken into consideration.

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

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

What is a Tankless Water Heater’s Temperature Rise

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

Putting Flow Rate and Temperature Rise Together

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

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

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

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

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

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

Are Tankless Water Heaters Worth the Cost

When it comes to purchasing a tankless water heater, many individuals question if the investment is worthwhile. Tankless water heaters, in contrast to tank water heaters, are a good investment because of their longer lifespan, lower maintenance requirements, and ability to provide continuous hot water on demand.

  • Tankless water heaters have a lifespan of up to 20 years, whereas tank water heaters have a lifespan of as short as eight years. Due to the fact that tankless water heaters do not have a tank that might malfunction and leak, the danger of water damage is reduced
  • Tankless water heaters do not require any maintenance because they do not have a tank. Tank models require yearly flushing maintenance to maintain the tank’s integrity, which is commonly neglected, resulting in a shorter tank’s lifespan as a result. Tankless water heaters have the ability to produce hot water on demand when needed. A 50-gallon tank water heater can get depleted in as short as 30 minutes of continuous usage and requires a minimum of one hour of recovery time
  • However, this is not the case.

Electric vs. Gas Tankless Water Heaters

Once you’ve calculated the appropriate flow rate and temperature rise, you’ll need to choose between electric and natural gas tankless water heaters for your application.

Electric Tankless Water Heaters Cost Less to Buy and Install

It is one of the key advantages of purchasing an electric tankless water heater over purchasing a gas-powered tankless water heater because they are less expensive. Tankless electric water heaters for the entire house normally cost between $500 and $700, but whole-house tankless gas water heaters cost between $1,000 and $1,200 or more. Aside from that, the cost of installing an electric tankless heater is much lower than the cost of constructing a gas-powered tankless heater. Following your confirmation that your home’s wiring is suitable with the type you’ve chosen, installing the electric heater should be a reasonably simple and quick task to complete.

In order to work, some electric water heaters require up to four 220v breakers, which dramatically increases the expenses of installation and operating.

For starters, you’ll need to build a ventilation system to safely exhaust any fumes that your water heater may produce.

Electric Tankless Water Heaters are Easier to Maintain

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

Electric Tankless Water Heaters are More Energy-Efficient

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

The production of electricity is already less detrimental to the environment than the combustion of natural gas, and the greater energy efficiency of electric vehicles further adds to the disparity between the two modes of transportation.

Electric Tankless Water Heaters Can Require Significant Electrical Upgrades

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

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

According to industry standards, one heating element is required for every 2GPM of water production in an electric tankless unit.

Gas Tankless Water Heaters Produce More Hot Water

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

For example, a normal 70 degree Fahrenheit (70 ° F) increase will result in an additional 5 gallons of hot water per minute from a gas-fired type.

Natural Gas is Cheaper than Electricity in Some Areas

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

Indoor or Outdoor Installation Options

In contrast to a standard tank-style water heater, which must be installed indoors, tankless water heaters may be installed either indoors or outdoors. Installation of your tankless water heater outside has the primary advantage of eliminating the need to install a venting system inside. Because electric units do not require ventilation, placing them outside provides no meaningful advantage in terms of energy savings. In warmer areas, it is possible to put a tank-style water heater outside; however, you will still need to construct an enclosure around it.

The majority of outdoor tankless water heaters include built-in freeze protection that can withstand temperatures as low as -30 degrees Fahrenheit.

Conclusion

Although you may not give it much thought, you use your hot water heater on a regular basis. Providing hot water whenever you need it is the one item that helps keep things clean and operating smoothly in any household! The question is, how do you choose the appropriate size tankless water heater for your household? Take into consideration the appliances that will be used at the same time. When two persons living in an average-sized home need to shower every day at different times of the day (for example, because they work opposing shifts), a 2 GPM model would be appropriate.

DISCLAIMER: The information provided on HomeInspectionInsider.com is not intended to be professional guidance.

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Hubert Miles receives a commission for recommending visitors and commerce to these businesses.

What Size Tankless Water Heater Do I Need?

Despite the fact that you may not think about it very often, you use your hot water heater on a regular basis. Providing hot water whenever you need it is the one item that helps keep things clean and operating smoothly in every household. The question is, how do you determine the proper size tankless water heater for your household? Consider how many appliances you will be using at the same time. For example, if two persons living in an average-sized home need to shower every day at different times of the day (for example, because they work opposing shifts), a 2 GPM model would be plenty.

See also:  How To Buy A Tankless Water Heater

HomeInspectionInsider.com makes no representations as to the suitability of the information it publishes.

It is owned and operated by Hubert Miles who is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by placing advertisements and links on their websites that direct traffic to Amazon.com (hereinafter referred to as “Amazon.com” or “Amazon.com Associates Program.”).

HomeInspectionInsider.com is also a participant in affiliate marketing programs with other web sites that promote home inspection services. Hubert Miles receives a commission for recommending visitors and business to these businesses.

  • The square footage of your home
  • The pace at which water flows through your home
  • Temperatures are rising
  • The number of people in your family

In this essay, we’ll go into further depth about each of these aspects. However, before we go any further into the subject, it is critical that you understand that you should never purchase a tankless water heater that is lower in capacity than you actually want simply because of price disparities. Before we get started, let’s have a look at a brief chart.

Sizing Guide for Residential Tankless Water heater

Household Occupants Usage Capacity Required (Measured in Gallon)
Electric Gas
1-2 people Regular/ Low 30 30
High 40-50 40-50
2-3 people Regular/Low 40 40
High 50 40-50
3-4 people Regular/Low 50 40
High 80 50-75
5+ people Regular/Low 80 50
High 80+ 75

1. The Size of Your House

In this essay, we’ll go through each of these things in further depth. However, before we go any further into the subject, it is critical that you understand that you should never purchase a tankless water heater that is lower in capacity than you actually require just because of pricing disparities between models. Before we get started, let’s take a look at a quick graph.

2. The Rate of Water Flow in Your House

We’ve established that tankless water heaters are different from traditional tank heaters in that they steam the water as it enters your home, rather than heating it. This implies that the rate at which water is released from your faucets is governed by the flow rate supplied by your water heater, not the other way around. Taking this element into consideration allows you to operate more than one faucet or shower at the same time without your faucet slowing down. Given that the typical flow rate of one shower head is 1.8 gallons per minute, it is possible that another shower will begin to run alongside the first shower at a rate of almost the same as the first shower.

Adding up the flow rates of the two showers will give you the flow rate that you will need for your tankless water heater.

We’ve included some average flow rates below to assist you in estimating the flow rates of the majority of your faucets.

  • Bathroom faucet flow rates range from 0.5 to 1.0 GPM
  • Showerhead flow rates range from 1.5 to 2.0 GPM
  • Kitchen tap flow rates range from 2.0 to 6.0 GPM
  • Dishwasher flow rates range from 1.5 to 2.5 GPM
  • And laundry washer flow rates range from 2.5 to 3.5 GPM.

3. Temperature rise

Following the calculation of the flow rate of each faucet in your home, you must decide how much heat your heater must create in order to provide you with the necessary heat in your water outlets. The needed temperature rise will be determined by taking into account the temperature of the water that enters your house and that of the water that you wish to have flow out of your tap when calculating the required temperature rise. We will suppose your home’s incoming water supply is 45°F and your shower (which is connected to your tankless heater) will deliver water at 105°F; the temperature raise necessary is 60°F.

To obtain the appropriate temperature in your shower, your heater must heat 1.8 gallons of water by 60 degrees Fahrenheit every minute, assuming that the shower flows at a rate of 1.8 GPM.

Some states are expected to have temperatures as high as 75 degrees, while others will have temperatures as low as 35 degrees, according to estimates.

If you’re not sure what it is, you may use the assumption that the temperature is 40 degrees to make sure you don’t underestimate the amount of temperature rise that will be required.

4. Your Household Size

This is yet another important consideration to bear in mind when installing a tankless water heater in your house. Your tankless water heater should be capable of managing occasional usages of hot water coming from specific taps without causing damage to the system. An additional point to keep in mind is when the most people are utilizing the service. What exactly does this imply? Every home suffers a spike in hot water use when they have visitors around, are organizing a wedding, or any other event of this nature.

Even though you may not be utilizing hot water all of the time, you must take into account the periods when your use spikes and use it as a starting point when determining your tankless water heater specs and requirements.

  • 2 showerheads with a total flow rate of 3.6 GPM
  • 2 kitchen faucets with a total flow rate of 4 GPM
  • 2 laundry machines with a total flow rate of 6 GPM

We’re looking at an estimated flow rate of around 13.6 gallons per minute, which may be higher than the average rate of flow in our area. Tankless heaters are designed to provide smooth heating operation at peak periods as well as during periods of average consumption. When sizing your tankless heater, consider the highest potential simultaneous usage.

Gas Tankless Water heater or Electric Tankless Water Heater?

Aside from the size, the other component that influences the operation of a tankless water heater is the size of the tankless water heater. For the most part, gas tankless water heaters can heat up to 5 gallons of water to 70 degrees Fahrenheit in a minute, but electric tankless water heaters can only heat 2 gallons of water to 70 degrees Fahrenheit in the same amount of time. We picked 70 degrees Fahrenheit since that is the temperature rise necessary for normal groundwater at 40 degrees Fahrenheit to reach a sweltering 110 degrees Fahrenheit.

Before making a purchase, always double-check the product specs for GPM and temperature increase ratings.

Tankless Water Heater Size FAQs

You may still have some queries about the size of the tankless water heater you require; we will attempt to answer them in this section.

Which sizes last longer?

Tankless water heater longevity is mostly determined by the type of tankless water heater used rather than its size. The lifespan of a gas tankless water heater is often greater than that of an electric tankless water heater. However, the type and brand of the product have an impact on the lifespan; however, in general, gas-fired tankless heaters have a lifespan of more than twenty years, whereas electric water heaters have a lifespan of seven to ten years.

Where can I find the right model size?

Departmental plumbing stores are likely to carry all of the available model sizes. For your convenience, you may want to try purchasing them online; however, make sure you carefully read the requirements to avoid any misunderstandings.

What size tankless water heater can I install myself?

Because you will require the skills of a skilled installation, this is not a do-it-yourself project.

The installation procedure is time-consuming and difficult. It entails gas connections, electrical circuits, propane units, and other such things. In such instances, the business will always recommend a tech person to customers.

What size tankless water heater is easier to maintain?

In comparison to bigger models, it seems obvious that smaller model sizes would be less difficult to keep up with. Regardless, you will want the services of a professional to do routine maintenance on your tankless water heater at regular intervals. This involves checking for leaks, inspecting the air vents, and cleaning the burner, among other things. If you reside in a hard water area, you should consider flushing your tankless water heater with vinegar every three weeks to prevent sediments from blocking the heat exchanger, especially if the tankless water heater is tiny.

What are the prices for different tankless water heater sizes?

Tankless heaters are priced differently depending on their size and model. A small gas-fired variant may be purchased for roughly $180, while larger models can be purchased for over $2,000. For $1,000, you may also acquire a model that is of medium size. Electric tankless heaters range in price from $90 to $900.

Conclusion

Following the calculation of your water flow rate and needed temperature rise for typical hot water consumption, make sure to account for peak usage periods so that your heater can provide you with hot water at all times. You can let us know if there is anything further you need to know after reading over all of the information we’ve provided in the comments section below.

What Size Tankless Water Heater Do I Need?

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

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

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

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

What a Tankless Water Heater Does

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

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

How to Calculate the Right Size of Tankless Water Heater

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

Determine Peak Hot Water Demand

When it comes to peak hot water demand, this is the greatest amount of hot water that your home may require at any given time. It is not intended to be a practical figure; rather, it is intended to ensure that your water heater is capable of meeting theoretical peak demands. Bathroom Utilities 2 gallons per minute for the clothes washer Estimate and include the maximum number of services that might be consuming hot water at any given time, such as the following: Shower = 2 gallons per minute 1.5 gallons per minute (gpm) in the kitchen sink Dishwasher = 2 gallons per minute Total flow rate: 5.5 gpm Alternatively, in a household with a large number of individuals who need hot water: Shower = 2 gallons per minute 2 gpm in a tub 1.5 gallons per minute at the bathroom sink 1.5 gallons per minute (gpm) in the kitchen sink Dishwasher = 2 gallons per minute Total flow rate: 9 gpm

Choose a Tankless Water Heater

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

You must compare and contrast the two sets of information in order to determine the most appropriate tankless water heater for your home.

See also:  What Water Filter Do I Need For My Whirlpool Refrigerator

Tankless Water Heater Pros and Cons

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

Compare Quotes From Top-rated Water Heater Installers

Estimates are provided without obligation.

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

It is necessary to first assess which fixtures are likely to be running at the same time in order to calculate your GPM. Then add up how much hot water (in terms of flow rate) is consumed by each and every fixture. Take, for example, the morning, when most people are taking showers or doing laundry, as an example of when to do laundry. Consider the following scenario: you have a two-bedroom, two-bathroom home with four occupants: Two showers are running in the morning, and a load of laundry is being loaded at the same time as one shower.

  • An average shower produces how many GPM?
  • Alternatively, how about a washing machine or dishwasher?
  • For a quick reference, you can refer to the helpful cheat sheet provided below.
  • 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.
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.

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.

Then deduct that amount from the desired temperature of your water. This is your temperature increase. Then you may look at the specification sheet of the tankless water heater you’re considering purchasing and see what the GPM rating is based on the temperature rise you calculated.

How Big of a Tankless Water Heater Do I Need?

The size of the tankless water heater you require is determined by the GPM of your peak hot water demand. In addition, your temperature rise is governed by the temperature of your entering water, which is deducted from your hot water setting. I’ll give you an example of what came out for me as a result of this exercise. Because I live in Boston, the temperature of my groundwater is around 47°F. Because I have little children at home, I keep the temperature of my water about 105°F. This is a safe temperature, and it will also help me save money on my gas bill.

  1. I determined my GPM to be 6 since our peak water use is caused by a shower, a washing machine, and a faucet all running at once.
  2. I produced a fairly extensive essay analyzing the top gas tankless water heaters for different sized houses that you might find useful.
  3. Anyway, I’m wondering what size tankless water heater would be the most appropriate for a family of four.
  4. Despite the fact that my variables are not the best case situation, the flow rate is reduced to 6.7 GPM from 9.8 GPM on the label.
  5. For the calculation, you may use a Rinnai tankless water heater sizing calculator to identify the most appropriate model for your needs and budget.
  6. If you live in a cold environment, the type of tankless water heater you choose will be influenced significantly by this issue.

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?

The British Thermal Unit (BTU) is a unit of measurement for the amount of energy required to heat water. As an example, consider the following formula: 1 BTU is equal to the amount of energy required to elevate one pound of water by one degree Fahrenheit. The greater the BTU rating, the greater the amount of water that can be heated. To ensure that the water is heated to the proper temperature, you must have a high BTU for a high water demand ratio. If you need to heat water for the entire house and your peak water demand is significant, you’ll need a boiler with a capacity of up to 200,000 BTU.

A modest family with a low water demand may get by with anything in the neighborhood of 140,000 BTU.

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.

  • They do not, in fact.
  • A hot water recirculating pump, on the other hand, will be required if you wish to have immediate hot water.
  • 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.
  • Is it possible to use a tankless hot water heater in conjunction with a well?
  • Additionally, when dealing with hard water from a well, a filter is recommended.
  • 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.
  • 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.
  • 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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