How Many GPM for a Tankless Water Heater Is Ideal For You?

The amount of hot water you need depends on what you’re using it for. So how many gallons per minute (GPM) for a tankless water heater is ideal?

On average, a tankless water heater can deliver anywhere from 2 GPM to 12 GPM of hot water.

If you want a tankless water heater for a single shower, you can get away with a unit that provides 2.5 GPM.

For a larger home and in need of hot water for multiple showers and appliances, a tankless water heater with 6-10 GPM will be suitable.

If you have a dishwasher or kitchen sink that needs to run constantly, your tankless unit will require more energy than if you’re just running your sink faucet or showerhead.

The number of appliances and their operation generally determines how much energy the tankless heater will consume. This article will help you determine what size of tankless water heater is right for your needs.

What is GPM in Tankless Water Heaters?

GPM stands for gallons per minute. It’s used to measure the amount of water that flows through a tankless water heater in one minute. This helps you determine how many gallons of hot water your tankless water heater is producing at any given time.

The higher the GPM rating, the more efficient your tankless water heater will be. Similarly, the more appliances you have running at once, the higher the flow rate will be.

In generic terms, the GPM is also known as the tankless water heater size because they are virtually size-less due to the absence of a tank. Hence, the GPM is considered the size of tankless heaters.

Finding the Correct Size of a Tankless Water Heater for Your Home

Woman adjusting water heater

The size of the tankless water heater you need for your home depends on how much hot water you use daily. To find the perfect size, it’s important to map out your home’s hot water usage.

Once you’re familiar with your household’s hot water needs, you’ll want to calculate the peak demand. Peak demand is the maximum amount of hot water needed in your home at any given moment.

After you’ve determined what hot water appliances are in your home and how many can be used simultaneously, it’s time to calculate the flow rate. This is a simple calculation that requires you to add up the flow rate of each hot water appliance used simultaneously.

For example: If you’re usually doing laundry at night, and someone else takes a shower at the same time, you’ll want a tankless water heater with a flow rate of 2.5 to 5 GPM.

Note: In the lingo of tankless water heaters, 4 GPM means a maximum of 4 gallons of hot water per minute.

Determining the Temperature Rise

Knowing the maximum flow rate won’t tell you everything, though. Another thing to take into account is temperature rise and where it sits against the flow rate your tankless water heater can provide.

Temperature rise refers to the difference between the incoming water temperature and the desired hot water outlet temperature.

The higher the required temperature rise, the more efficient the tankless water heater will need to be. For example, if the average groundwater temperature is 60°F and you want an output temperature of 120°F, then the temperature rise would be 60°F. To calculate the temperature rise, subtract the incoming water temperature from the desired output temperature.

How Many GPM for a Tankless Water Heater Should You Look for?

In most two- to four-person households, a tankless water heater with a capacity of 6-10 GPM is ideal. It can provide hot water to multiple fixtures (showers, kitchen faucets, and laundry machines). If you have a larger household, you may need a higher-capacity unit. Tankless water heaters with 11+ GPM capacities are better equipped to handle larger households and multiple hot water outlets.

If you have a smaller home, you might be able to get away with a smaller-capacity tankless water heater. However, make sure your water heater can meet your household needs! If you have a two-person household, but your hot water needs are greater than the output provided by a smaller tankless water heater, you may run into issues.


What size tankless water heater do I need for a family of five?

For a family of five living in one home, a higher GPM tankless water heater is necessary. If you live in a northern region, your tankless water heater should be at least 10 GPM. If you live in a warmer climate, you won’t need a unit as powerful and can opt for one of 7 GPM.

How many tankless heaters do I need?

If your home is large and an 11+ GPM tankless water heater can’t meet your family’s needs, you’ll need two tankless heaters. Otherwise, a single tankless water heater will do the job.

Are tankless water heaters worth it?

Yes, tankless water heaters are worth it for many homeowners. Tankless water heaters provide an endless supply of hot water on demand and can save money on energy costs in the long term. They also take up less space and are more efficient than traditional water heaters.


So, how many GPM for a tankless water heater is ideal? Well that depends on the size of the home and the number of fixtures used for hot water.

Generally, a tankless water heater should be able to provide a minimum of 2.5 GPM for a single bathroom and up to 8-10 GPM for a large home with multiple bathrooms. In addition, it is important to consider the incoming groundwater temperature to determine the proper GPM for a tankless water heater.

With years of experience under his belt, Adam decided to put his water heater knowledge to work. By providing high-quality content and expert guides, Adam hopes to help anyone looking for expert water heater advice.