What Size Tankless Water Heater Do I Need

Recently, I came up facing a problem. The problem was with the size of my tankless water heater. Being an essential investment for my home, it is equally important for me to find the right size for my house. Especially, tankless water heaters are the best choice nowadays.

For this problem to be solved, I had to search online. Finding the solution was not easy as pieces of information are scattered around. But many people are constantly looking for the solution. So, what size water heater do I need? I have gathered up some of the information, and now going to provide you this information. Hope, this will help you find the perfect match for yourself too.

How the water heater size is measured?

The first thing that comes in mind is the measurement system. Without knowing the unit, it is hard for one to replace a tankless water heater from the regular water heater. In the US, the imperial system is quite popular. The unit is always measured in gallons. 40 to 60 gallons are popular ones. But other countries use the metric system. They like to measure it in liters.

What size tankless water heater do I need?

What size do you require? – mainly depends on some important consideration. These considerations follow the measurements. Combining both, you can get the right size for you. This portion of the article is going to talk about all those considerations.

  • The fuel sources

Do you want to get the electric tank less water heater or the gas operated one? This is the first key consideration for any purchaser. Because one needs to get the water heated up for various household purposes.

  • Size

The size of the tank-less water heater is also important. Making sure the water tank will fit in the location of your house is a key consideration. The physical size and design of the water heater are crucial in this case. But tankless water heaters are relatively smaller in size. Fitting the appliance is not a hard nut to crack anyway.

  • Storage

Now thinking about the storage is also important in this case. But why? When you can calculate the gallon per minute and appropriate ground temperature, the job gets easy.

The size of the gallons mainly depends on your family member and the usage. For 1 to 2 members, 30 gallons is more than enough. A family consisting of 2-3 members require 40-gallon capacity on the heater tank. Like that a family consisting of 3 to 5 members need 50-gallon reservoir. A family of more than 5 members needs 80 gallons of storage.

Keeping all these in mind, finding a suitable tankless water heater is tough. But after knowing the gallon per minute, you will get to choose the perfect one for your home.

  • Usage

Figuring out the user can always help in choosing a suitable tankless water heater. If you get to know how much you will get out of the appliance and match the usage, it is easy. For 1 or 2 people, 40 gallons is enough to do all the household job. But the universal fact is that a family of four generally require 40 gallons at least. You can add 10 gallons more for each individual.

But one thing for sure, for bathing a person needs at least 15 gallons or maybe more. Let’s just say that, a person at least needs 20-25 gallons per day. With all the household task in mind, you need to find the tankless water.

 Calculate the peak hour usage for yourself and determine how many gallons you need the whole day. Tankless water heaters are a little slow in producing hot water. So, the estimated calculation will help you to make a combination of both.

  • Flow rate

Determining the maximum number of device usage and calculating the flow rate is very important. When I say the flow rate, I mainly refer to gallons per minute. Generally, you can get 5 gallons per minute with many gas-fired water heaters. An electric water heater can heat less water.

You can get 2 to 3 gallons at least. But it is the combination of your user devices that will determine your flow rate. What household device needs to get the water? Find that out. Calculate their flow rate. Try to match it with the water heaters flow rate. That is all.

  • Ground temperature

Basically, one needs a water heater that will produce a temperature rise of 55 degrees. In many areas this is important. Not all the areas temperature are the same. rather they are a little different. So, checking out the ground temperature is equally important. This will affect the water heating process.

Some important FAQ

What size tankless water heater do I need to replace a 50-gallon water heater?

In order to do so, finding a water heater that produces 7-9 gallons per minute is a good choice. But mainly the calculation depends on the rise of the heat. Nothing more. You can even get 9 gallons per minute. Depending on your usage, if you want to replace your 50-gallon water heater, find a tankless water heater with 7-9 gallons per minute water production.

What temperature I should set my tankless water heater?

This is a tough question. You will find all the information from the instruction from the manufacturer. Also, this largely depends on the ground temperature. Check that out, you will get to know the rest.

Does the water heater has any advantages? 

Yes, it has a lot of advantages.


The problem often arises when there is a question of what size tankless water heater one should choose to replace the regular water heater. The answer is always not easy. There is a lot of information online and you cannot relate one with the other all the time. So, confusion is bound to happen. Keeping that in mind, when I search for a solution, had to face the same problem. But the following article was just to get you out of all these confusions. Nothing more.

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