What Size Tankless Water Heater Do I Need?

Whether you live in a hot climate or a cold climate, having a water heater in your house is a great luxury, especially for showering. They’re comfortable, they’re affordable, and they’re overall easy to set up too.

However, the size can get difficult to pick, especially since there can be more than one shower or faucet running simultaneously. Because of this, many people get confused and ask themselves, “what size tankless water heater do I need?”

If you don’t want to spend much time calculating the exact necessary size, an 8 GPM water heater will be enough for most people. But for bigger households with more than 3 people, a 10 or 11 GPM one can work well.

We’ll be covering all about tankless water heaters and what size you should pick today. Let’s begin. 

How To Know How Much GPM You Need

The first step to figuring out exactly what size your tankless water heater needs is to find how much GPM or gallons per minute you might use simultaneously. 

As a rough estimate, a bathtub can use up to 4 GPM while a showerhead can use between 3-5 GPM. These will use the most GPM as other things such as your faucet or dishwasher won’t use more than 2 GPM. Laundry machines usually use a maximum of 5 GPM, too.

So depending on how many of these facilities you use in your house and the number of people using them, you can calculate exactly how much GPM you need. But usually, even with 1-2 bathrooms and 2-3 people, you won’t need any more than 8 or 10 GPM. 

What Size Tankless Water Heater Do I Need

Now that you have a good idea of calculating the GPM of your household, you’re ready to pick a tankless water heater.

As mentioned earlier, you won’t need more than 8 GPM for a household of two or more than 11 GPM if you have a household of four or more. So you’re good to pick any tankless water heater with the required GPM capacity that fits your budget. 

However, sometimes, you’ll need to pick a higher GPM value than you might need since a tankless heater’s GPM or flow rate depends a lot on the groundwater temperature and climate. 

For example, if you live in a cold area, the water will be colder and it’ll be harder for your heater to heat it up. Since your heater will be working much harder, the GPM can decrease substantially depending on how cold it is. 

But in hotter countries, the max GPM can be double compared to colder climates, allowing you to use more hot water simultaneously. So if you live in a cold country, make sure to get a heater with 2-4 GPM higher than your required amount.

Do I Need More Than One Tankless Water Heater For Bigger Houses?

If you live in a bigger household with more than 4 people, you might be wondering if you need more than one unit. But most of the time, one big unit such as a 50 gallon gas water heater will be enough, even for 4-6 people. 

However, if you have a really big house with more than two bathrooms and over 6 people, an 11 GPM gas tankless heater along with a 15-25 kW electric heater will be more than enough.

The gas heater will usually be able to take care of everything, but for times when all the bathrooms are running simultaneously, the electric heater can help. So no, no matter what, you won’t ever need more than one big water heater unit. 


  • Should I Get A Tankless Or Tank Water Heater?

Ans: Tankless water heaters and tank water heaters both have their advantages and disadvantages. However, the biggest advantage of tankless heaters is that they use much less energy, so you’re better off getting a tankless heater.

However, they only heat the water when you need it to, so you can’t heat it when there is no electricity. Tank water heaters keep the water hot all the time so you can use it whenever you want, but they’ll use much more energy. 

  • Do Tankless Water Heaters Cost More?

Ans: Yes, tankless water heaters can cost up to three times more than a traditional water heater, and they take more effort to install in your house too. But even with this huge disadvantage, a traditional tank water heater will be much more expensive to maintain as it uses more energy. 

So even though it’s more expensive, we’d still highly recommend you to get a tankless water heater. They use much less energy and are better if you need warm water often. 

  • Are Tankless Water Heaters More Durable?

Ans: Yes! Tankless water heaters are significantly more durable than regular tank water heaters. This is because a traditional tank water heater can last 10-15 years, but a tankless water heater can last double that amount at 20-30 years. 

You’ll usually get a better warranty or guarantee with tankless water heaters too, so they’re better in almost every way compared to tank water heaters. 


Hopefully, you aren’t wondering, “what size tankless water heater do I need?” anymore. To recap, you’ll usually need a 6-8 GPM tankless heater for two or three people and a 9-11 GPM heater for four or more people. 

But as a final tip, we’d highly recommend you to get electrical heaters if your household has less than 3 people, especially if you’re in a relatively hot climate. This is because, with 2 people, you usually won’t need to run two showers simultaneously, and even if you do, a 10-20 kW electric heater can usually do the job just as well.

But with all that being said, good luck choosing, and cheers!