Richmond Virginia Plumbing

What Size Tankless Water Heater Do I Need?

Posted on January 19, 2022 in Bathrooms, Plumbing

Once you’ve made the decision to install a tankless water heater, you will then likely ask yourself, “What size tankless water heater do I need?” There are several factors to consider when choosing the output capacity, or GPM, of a tankless water heater. Keep reading to learn more about the perks of tankless water heaters and the size considerations to keep in mind.

No one wants a cold shower but how do you know what size tankless water heater you need to make sure your water is hot when you need it?

About Tankless Water Heaters

Tankless water heaters have become an increasingly popular choice in recent years. These can run on either gas or electricity and can save homeowners many hassles and thousands of dollars in the long term.

With a tankless water heater, your hot water supply is continuous — meaning you will never run out of hot water if multiple family members need to take a shower back to back in the morning. You are not limited to how much water can fit in the tank and be heated at one time.

Tankless water heaters offer homeowners and residents a number of other benefits over traditional water heaters. For instance, tankless water heaters:

  • Take up less space in your home
  • Heat only the amount of water that is needed when it is needed
  • Help save money on energy expenses
  • Require less maintenance
  • Are safer and better for the environment
  • Have a longer life span (they can last up to 10 years longer than a traditional water heater!)

Size Considerations for Tankless Water Heaters

The size of a tankless water heater is measured in terms of GPM (gallons per minute). This is also known as the “flow rate.” In addition, you’ll want to look at the “temperature rise,” which is the difference between the cold water temperature flowing in and the desired hot temperature that will be flowing out.

Determining what size tankless water heater you need comes down to one main thing: what size is the right size to keep up with your household’s demand for hot water? Of course, several factors go into making that determination.

Family Size

One of the biggest factors for knowing how much hot water you will need is your family size. How many family members will be taking showers, washing hands, doing laundry, running the dishwasher, and generally using up hot water?

If you have a large family, you will be glad you upgraded to the larger water heater, especially during times of peak consumption.

Home Size

Similarly, your home size matters in determining what level of tankless water heater to get. The most important factor is the number of bathrooms you have, but you will also need to look at how many appliances you have and the likelihood of using multiple water sources at once. 

Plus, if you have a large home, you may want to consider a unit with a higher GPM, as the water will take longer to travel to all areas of your home.

Water Consumption

Your family’s hot water habits matter a great deal as well. What you use and how you use it will impact the right fit for your circumstances.

Typical household activities use up anywhere from 1 to 5 GPM. For example, a shower will use 2 to 5 GPM depending on the showerhead, a dishwasher will use around 1.5 to 2.5 GPM, a standard faucet uses just 1 GPM, and a washing machine uses between 1 and 2.5 GPM. The more energy-efficient your appliances and fixtures are, the less water you will consume.

Local Climate

Your location and weather in the area can affect how many GPM you will need and how quickly you can expect your tankless water heater to run. Areas with colder climates, with systems that run off of groundwater, will require significantly more energy to heat and deliver the water to your home.

To put it simply, the warmer the climate, the more accurate the stated GPM, and the colder the climate, the more your unit will struggle to heat the water you require in the time that you need it.


No one wants to spend more money than necessary. For many families, the cost is the number one factor when it comes to buying new appliances and household goods. The larger the water heater you select, the higher the price tag. Bigger water heaters will also use more energy and thus increase your utility bills.

When making your decision, you will also need to keep in mind the costs for installation, which tend to be more expensive for tankless water heaters, and the costs for maintenance, which tend to be lower for tankless water heaters. 

A tankless water heater can cost a bit more upfront, but it should also last you many more years to come. One way to consider financing your tankless water heater purchase is through a home equity line of credit (HELOC).


While all tankless water heaters are compact, you may need to consider your available space when selecting the size of your new water heater, especially if you are trying to squeeze it into a small area, such as in an RV. 

In general, the lower the GPM, the smaller the size of the unit. For example, a 3.51 GPM electric water heater by Rheem is 3.5 x 14.5 x 18 inches, while a 9.5 GPM natural gas water heater by Rheem is 9.75 x 18.5 x 27.5 inches.

Let RJ Tilley Help You Decide What Size Tankless Water Heater You Need 

While tankless water heaters aren’t cheap, they are very much worth the investment over time. If you are ready to select and install a tankless water heater in your home, visit the link below to learn more.

Read About Tankless Water Heater Installation