What Size of Tankless Water Heater Do I Need- Heater Size Calculations

Tankless Water Heater Sizing Calculations

Size is one of the basic considerations while buying a tankless water heater because it matters a lot in daily life. Most people get confused and asked questions about what size of tankless water heater do I need? It’s not so simple to determine the size as depends upon some factors including your family members to your bathroom or home size.

Hhow to size tankless water heater is another frequently asked question? At the end of the article, there is a complete guide on this query.

Tankless water heater GPM calculators helps a lot to determine the size of a heater depending upon energy and water limit.

Let’s know firstly why it’s important to know the size of the heater for your house or any other outdoor acticity. Suppose if the water heater is too small then it would not be able to fulfill your family’s needs.

It might happen that a person needs to water for other family members to run off the shower because the heater is too small. And small heater can only allow one shower at a time to use.

Now take the opposite examples and think if your water heater is too large. In this situation, it will use more energy, and end result would be high electricity and gas bills. The reason is that it’s too sharp and provides water in a very fast way.

How to Size Tankless Water Heater?

The most important need and fact about how to size a tankless water heater which is important as compared to many other factors. There are some tankless water heater sizing calculators and all of this measures the size according to their specific units.

Some of them measure the values in GPM and are tankless water heater GPM calculators. These tankless water heater sizing calculators provide a good service to calculate size.

 But if you still are stuck for how big a tankless water heater do I need then this post is for you. Read the following guides carefully and then decide according to your need.

Our overall experiments show that it’s not easy to size a tankless water heater but using some tricks makes it dead easy.

How to Determine Tankless Water Heater Size

Let’s now learn about how to determine size following tankless heater sizing calculations.

Step#1 Calculate How Many GPM for Tankless Water Heater

If you want how many GPM water heaters do I need for my house then read this point. It’s specifically related to the GPM sizing of the tankless water heaters.

Calculating the GPM rate depends upon how many individual fixtures at your home does use this water heater. And how much hot water you need for daily activities.

It is a way to determine how many gallons per day a heater can provide. GPM is gallons per minute which is a unit of water product. Given by the equation you can determine how it’s important:

GPM You Need= Sum of All Individual Appliances GPM rates Given at the same time

So, if you don’t know about a specific product or its original number you can estimate it by GPM size and value. Use and compare the same information with tankless water heater size chart and find the answer about “what size of tankless water heater do I need a calculator?”. After that, it’s easy to find size by comparing individual fixtures and GPM rates.

Step#2 Determine Your Temperature Need

After finalizing the amount of water you need, the very next step is to determine and look for the temperature you need. Some people demand high temperature but some needs normal for their normal tasks.

This temperature differs from person to person but most people do ask and like 120 Degrees Fahrenheit which is the very valuable and ideal temperature for tankless hot water. But if you are in a cold water area, you can increase units using thermostat reading.

Note: Below is a picture showing how to determine temperature rising according to your area and then decide to buy a tankless heater.

Now the important question is how to find a specific temperature that is suitable according to their area and working environment. It’s a very easy and unchallenging task. Here is the equation to find it

Temperature Rise Needed= Desired Water Temperature- Incoming Ground Water Temperature

In this way, you can find out the temperature of your area and another factor to determine how big a tankless water heater you need. It’s an important option in choosing the size of a tankless water heater that provides an estimated value that is very correct up to an extent.

Step#3 Your Power Source

Determining your power source is another important and basic consideration that is missed by many people. It does not mean that a gas or an electric tankless water heater is best for you but you need to determine your power source firstly.

Electric tankless water heaters are recommended to use where warm water is available in groundwater. But for gas tankless water heater it changes your recommendations and demands.

As compared to electric heaters which are recommended for the point of use tankless water heaters, gas heaters are used for large homes. And probably where warm water is unavailable underground.

Here are some questions which you need to ask yourself to determine your power source easily!

  • Do you have gas or electricity as your main power source?
  • What is most affordable to use if you have both?
  • Availability hours of gas or electricity?

These are some common and basic questions that everyone should be answered to install a heater according to a specific size without any hurdle.

Overall our experiments and terminologies show that electric tankless water heaters are more affordable and easy to use everywhere. Moreover, these are easy to use.

But gas tankless water heaters are affordable and cheap to use rather than electric heaters. All it depends upon availability and your need. You can choose and select any one of these.

Tankless Sizing Overview- Water Heater Sizing Calculations

Following this section, there is some complete information about tankless sizing overview based on some units which are in use by calculators.

Moreover, if you are known of these sources, you can easily determine the whole process and procedure to find the best size tankless water heater for you. There are two main factors:

Flow Rate

Flow rater is measured in GPM which is about how much hot water you need at a time or how gallons per minute you need at a time. It’s also an answer for how to determine GPM for the tankless water heater. Here is a common example of flow rate:

ItemsFlow Rate (GPM)
Bathroom sink faucet1.0
Tub faucet2.5
Kitchen faucet1.5
Washing machine2

With the above examples, you can estimate how many GPM do I need for my house.

Temperature Rise

The difference in incoming cold water from the ground in a specific area and your desired hot water temperature is temperature rise.

What Size of Tankless Water Heater Do I Beed for a Family of 4?

If you are a family of four members, here is a guide for you about how to consider the size of a tankless water heater and what is an ideal size of a heater.

Here are some considerations and calculations for you and you can determine the size of a water heater easily by maximum GPM value. Suppose a family of four with the following prospects:

  • Dishwater with 2GPM
  • A kitchen sink with 3GPM
  • 2 Showers for 2.5 GPM

So, according to our estimation, experimentations the average size which you need for a family of 4 members is 6.5 GPM accordingly.

On the other hand, you can determine the temperature rise for better understanding. For example, if you want 120 degrees F of temperature and your ground temperature is 77 degrees F, then the average temperature rise is 43 degrees F.

What Size Tankless Water Heater for a Family of 5?

For a family of five, the requirements for a tankless water heater are almost the same as for a family of four. However, there are some changes that are depending upon a lot of features. Our experience shows that overall values are the same.

Let’s suppose the family is using 2 showers, a dishwasher sink, and bathroom faucets. This example is for a family who lives in Oklahoma where the temperature is 77 degrees F and the family wants to get water with 120 degrees F value.

In estimation with the previous example, think about the equations and now the estimated temperature rise value is 643 degrees F here. Taking the values of all GMP for the same as the previous family, the overall size of the water heater is 9.5 GMP which is an average water heater size.

What Size Tankless Water Heater to Replace a 50 Gallon?

A tankless water heater with a 10GPM size is enough and ideal to replace a 50 gallon and this value is the same for the electric tankless water heater and gas tankless water heater.

Important Note

If you have been using a tankless water heater, then instead of replacing its parts we suggest buying the best-sized water heater depending upon your requirements.

Last Words- What Size of Tankless Water Heater Do I Need

After the overall suggestions and our guide, we hope that now you can estimate how much big size do you need for your family according to need. There are two basic steps which you need to follow i.e.:

  • To determine the GPM
  • To determine the temperature rise

If you have further questions, you can freely ask us any time. Do comment us and find the answer within 24 hours. If you want the best tankless water heaters, do read our guide and reviews. Tankless water heater dimensions are another way to specify your requirements.

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Bella Rose
By Bella Rose

Hello Everyone! I'm Bella Rose. I believe in spending wisely when it comes to knowing about home and kitchen appliances. Spend smartly and make your home smart.

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